Natural Indigo(CHAPTER XV. Indole Group.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

INDIGO has been known in Asia from a remote period of antiquity, and there exist very ancient records in Sanskrit describing its methods of preparation. The Romans appear to have recognised it only as a pigment (indicum), but evidence as to its use as a dye by the ancient Egyptians has been abundantly proved from the examination of mummy cloths. Its employment in Europe was very limited until in 1516 when it began to be imported from India by way of the Cape of Good Hope, but its introduction in large quantity did not occur until about 1602. Owing chiefly to the opposition of the growers of woad, its European rival, as a dyeware it met with much opposition, and various laws were enacted both on the Continent and in England prohibiting its use. It was called a "devilish drug," and was said to be injurious to fabrics. In 1737 its employment was legally permitted in France, and from this period its valuable properties appear to have become gradually recognised throughout Europe.

The most important plants which yield indigo are those of the genus Indigofera belonging to the natural order of the Leguminosa; these have been cultivated in India, China, Egypt, the Philippines, Caracas, and Brazil.

For the purpose of indigo manufacture the Indigofera tinctoria (Linn.), I. sumatrana (Garrtn.) (the Indian plant), I. disperma (Linn.), I. argentea (Linn.), and I. arrecta (Höchst.) (the Natal plant), the I. paucifolia (Delile) (Madagascar plant), and I. secundiflora (Poir.) (Guatemala plant), have been mainly used, though certain less valuable varieties, viz. the I. pseudotinctoria (R. Br.), I. angustifolia (Linn.), I. arcuata (Willd.), I. caroliniana (Walt.), I. cinerea (Willd), I. longeracemosa (Boiv.), I. cœrulea (Roxb.), I. endecaphylla (Jacq.), I. glabra (Linn.), I. hirsuta (Linn.), I. indica (Lam.), I. mexicana (Benth.), I. leptostachya (DC.), have been employed. In Japan, China, and Russia the plant usually cultivated has been the Polygonum tinctorium (Ait.), but the Isatis tinctoria (Linn.), or woad plant, at one time very largely grown in Europe, is now only used in very limited quantity as an adjunct in the dyeing of indigo (woad vat). The native source of indigo in Western Africa appears to consist almost entirely of the Lonchocarpus cyanescens (Benth.) (Perkin, J. Soc. Chem. Ind., 1907, 26).

¹ Wrightia tinctoria
² Gymnema inodorum
³ Koanophyllon simillimum
⁴ Calanthe triplicataOther indigo-yielding plants are the Nerium tinctorium¹, Gymnema tingens² (Spreng.), Eupatorium laeve³ (DC.), Tephrosia tinctoria (Pers.), Marsdenia tinctoria (R. Br.), and certain species of orchids such as the Phaius grandiflorus (Reich.), and Calanthe veratrifolia⁴ (R. Br.).

In addition to these, various plants, of which the Mercurialis perennis (Linn.), Fagopyrum esculentum (Moench.), Fraxinus excelsior (Linn.), Baptisia tinctoria (R. Br.), and Rhamnus alaternus (Linn.) (Georgievics, Der Indigo, 1892) may be given as examples, are stated to yield indigo, or a very similar colouring matter, but this requires confirmation.

The production of indigo from the indigo plant is of a simple character and consists mainly of two processes, viz. a steeping of the plant with water (fermentation), followed by the oxidation of the solution with air in a separate vessel. Until very recently but little modification appears to have been introduced into this ancient process, and there is also but little variation to be found in the main features as described by Bancroft ("Philosophy of Permanent Colours," 1813), Crookes ("Manual of Dyeing and Calico Printing," 1874), Bridges-Lee ("Indigo Manufacture," 1892), Georgievics (loc. cit., 1892), and Rawson ("The Cultivation and Manufacture of Indigo," J. Soc. Dyers, 1899).

* It has long been known that the percentage of indican rapidly disappears from the leaf in the freshly plucked moist condition, and on this account it is advisable that the plant when cut down should be dealt with at once. On the other hand, it has been the practice to a small extent in certain districts to airdry the leaf before proceeding with the manufacture of indigo. In order to determine if when air-dried under ideal conditions, the leaf in these circumstances loses a material amount of indican, experiments were made by Watson (Jour. Chem. Soc. Ind.,1918, 37, 81) with indigo plant specially grown for the purpose. The leaf when gathered was divided into two portions, one of which was analysed at once, and the second dried by spreading in a thin layer upon filter paper in a north verandah for three or four days until constant in weight.

The analyses were carried out by the isatin method (loc. cit.) with 10 grammes of leaf weighed in each case in the fresh condition, and the results expressed as indirubin indicate that a serious loss of colouring principle does occur in these circumstances:
(a) Fresh Leaf. 0,1008 / Air-dried Leaf. 0,0568 (b) Fresh Leaf. 0,0825 / Air-dried Leaf. 0,0610 (c) Fresh Leaf. 0,1057 / Air-dried Leaf. 0,0763 Directly the plants are cut down they are tied in bundles and brought to the factory without delay, because it is necessary that the material should be operated on at once.* The tanks for the extraction (steeping vats) and precipitation of the indigo by oxidation (beating vats) are sometimes of stone, but more usually of brickwork lined inside with cement, and are respectively ranged in two rows one above the other, so that, the former can be drained into the latter. The steeping vats may have a capacity of about 1000 cubic feet, and are usually of much smaller dimensions than the beating vats, of which less are consequently required. According to Rawson (loc. cit.), who describes a small indigo factory, each range of beating vat runs the whole length of six steeping vats, and has a width of 13 feet 6 inches.

Into each of the upper tanks the bundles of the plant are tightly packed (preferably in a horizontal position, Bridges-Lee, loc. cit.) on the top of this is laid a horizontal trellis of bamboo, and the whole is wedged down into the tanks by means of timber, so that the material is unable to float during the fermentation process. Water is then run in, in such quantity that the bundles are entirely submerged. After about two hours an active fermentation is observed, and the surface of the liquid becomes covered with froth owing to the evolution of a mixture of carbon dioxide, oxygen, and nitrogen (Georgievics, loc. cit.); in the later stages (Rawson, loc. cit.) either marsh gas or hydrogen or a mixture of the two is freely produced. After ten to fifteen hours, according to the prevailing temperature of the water, the straw-yellow, orange, or olive-green coloured liquid is drawn off into the tanks below, and submitted to oxidation with air.

This may be accomplished by "hand beating," by machinery (the beating wheel), by blowing air through the liquid, or by the showerbath method. During this operation the colour of the liquid gradually changes, becoming first dark green and then blue, and considerable frothing is produced. When it is observed that the indigo precipitate or "fecula" readily settles, the beating is discontinued and the mixture allowed to rest for some two hours. The supernatant liquid, or "seeth water," having been drained off as completely as possible, the indigo sludge or "mal" is led into a reservoir inside the factory, from which it is subsequently elevated by means of a hand pump or steam injector into a large cauldron known as the "mal boiler". It is here heated by direct fire or by the admission of steam, and this has for its object the prevention of a further fermentation, the solution of certain brown impurities, and a more complete granulation of the "mal".

The product is then run on to a filter known as a "table," consisting of stout cotton or linen cloth stretched over a shallow rectangular basin of stone or cement, with a drainage opening at one corner, and allowed to remain until it has the consistency of a stiff paste. In order to remove excess of moisture the indigo is transferred to perforated wooden boxes lined with sail cloth and cautiously pressed. Finally, the resulting slab is cut into cakes by means of a guillotine or metal wires and allowed to dry at the ordinary temperature on trellis-work shelves in a specially constructed drying house.

Butea gum.(CHAPTER XIV. Coumarane Group.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

The dried juice of Butea frondosa (Roxb.) is often sent into the market instead of genuine kino. It forms black-brown, slightly lustrous, brittle lumps, has an astringent taste, and yields catechol by dry distillation.

Sylvander Schweder: Om trähus-byggnaders anstrykning med ljusa färger

Hushållningsjournal, syyskuu-lokakuu 1807

De egenskaper man fordrar av en god färg är: att den skall vara behaglig för ögat, oföränderlig, häftande, täckande, billig och bevara träet från röta. Färgens häftande beror på klisterämne, järnhalt, kalkblandning, färgens finhet, anstrykningens tjocklek och träytans grovlek. Användbara klisterämnen: lim, mjöl, olja och mjölk. Av lim och mjöl, som vanligast används torde mjölet vara det bästa och billigaste.

Det är inte säkert att den olja man av vana blandar i har någon verklig nytta. En fransk kemist Cadet de Vaux har funnit att mjölk är användbar som fernissa. Professor Lampadius i Freyberg har undersökt föreningen av kalk och äggvita, i tillstånd av ost. Denna förening har tidigare varit känd som ett kitt att laga porslin och glas med, men genom tillsats av fint kvartsmjöl har han gjort den brukbar även såsom färganstrykning.

Varning för att slå krita, kalk och viktril i färgen.

Denna avhandling tar endast upp inhemska färger, såsom rödfärg, gulockra och grönjord. Därtill kan läggas alunslam och blålera.

Bergrådet Rinman har funnit särskilt blåleran tjänlig till färganstrykning. Av myrmalm från Kvarsebo i Östergötland har man bränt en brun färg som kan uppfylla vårt behov av umbra. Skada blott att hela upptäckten trots uppmuntran av Patriotiska sällskapet kommit i förgätenhet. De färger, som är så dyra, att man inte kan nyttja dem till vidsträckta ytor, men väl till ornament är gula (Mengel och Räuschgelb).

Den röda färgen Colcotharn, vilken säljs under namn av brunrot och ger vackra både allvarsamma och glada nyanser. Den gröna färgen mineralgrönt, Schelesgrönt och Braunschweigergrönt tillreds också i Sverige.

Av blå färg finns endast berlinerblått, som inte finns i tillräcklig mängd i Sverige. Litet har hittats i Vemmenhög i Skåne men torde inte vara något att hoppas på.

Nu följer 15 kompositioner, alltså färgrecept.

En viktig omständighet är att hindra träet från röta. Ännu vet man inte vilken färg som är den bästa. Det är viktigt att färganstrykning sker med het färgsoppa, som lättare tränger in i träet. Om färgborstarna, som man har, gjordes större skulle anstrykningen bli jämnare och dessutom gå fortare. Man skall inte blanda mer färg än som går åt, ty den försämras om den blir gammal. Att färgsoppan ständigt skall omröras och att man målar på uppehållsdagar känner alla rödmålare till.

Kino.(CHAPTER XIV. Coumarane Group.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Kino consists of the dried astringent juice of various trees, and though now practically obsolete, came into commerce in the form of small semi-opaque reddish-brown fragments. There are numerous varieties of this material, of which the following are the best known:

Malabar kino (Pterocarpus marsupium), African or Senegal kino (Pterocarpus erinaceus), West Indian kino (Coccoloba uvifera), Bengal kino (Butea frondosa), and Australian kino (Eucalyptus spec). Among these, Malabar kino, at one time medicinally employed in Europe owing no doubt to its astringent properties, appears to have been the most frequently examined, though as the results obtained by distinct workers have not always been in agreement, it is probable that material experimented with has in certain cases consisted of some other variety.

When distilled Malabar kino evolves catechol (Eissfeld, Annalen, 1854, 92, 101), and by fusion with potassium hydroxide, phloroglucinol and protocatechuic acid are obtained.

According to Etti (Ber., 1878, 11, 1879) when kino is digested with dilute hydrochloric acid, and the liquid extracted with ether, a substance kinoin, C₁₄H₁₂O₆, crystallising in colourless prisms, can be isolated. This compound is readily soluble in hot water, and when heated with hydrochloric acid to 130° yields catechol, gallic acid, and methyl chloride, and at 120° is converted into an amorphous red compound, C₂₈H₂₂O₁₁, the so-called kino red. Kino red is itself present in kino and forms a red resinous powder sparingly soluble in water, and the solution thus obtained gives a dull green coloration with ferric chloride.

Perkin (Chem. Soc. Trans., 1902, 81, 1173) obtained in a similar way from a sample of kino (botanical origin uncertain) a small amount of crystalline substance, which he regarded as kinoin, and which possessed yellow dyeing properties with aluminium mordanted calico.

White, however (Pharm. J., 1903, (ix.), 16, 676), was unable to obtain kinoin from Malabar kino, and again, Simonsen (Chem. Soc. Trans., 1911, 99, 1532), who submitted material of undoubted botanical authenticity to critical examination, could only isolate a small amount of catechol by Etti's method. From kino itself Simonsen, by the action of methyl sulphate and potassium hydroxide, obtained the trimethyl ether, C₁₅H₁₁O₄OMe)₃ a colourless amorphous powder which could not be crystallised. That kino thus contains three hydroxyl groups was confirmed by an examination of the acetyl derivative, an amorphous brown powder of the formula C₁₅H₁₁O₄(OAc)₃

By oxidation with permanganate, kino methyl ether yields veratric acid, whereas by fusion with alkali, kino itself gives protocatechuic acid. By neither of these decompositions could the formation of phloroglucinol or a phloroglucinol derivative be detected, and the statement of Eissfeld that he obtained phloroglucinol from kino appears, therefore, to be incorrect. Smith (Roy. Soc. N.S. Wales, 1895, 30, and 1896, 135) isolated from Australian kinos derived from Eucalyptus hemiploia (F. and M.) and E. calophylla (R. Br.), by means of ether, a substance aromadendrin, melting-point 216°, to which the formula C₂₉H₂₆O₁₂ was assigned. This crystallises from water in colourless needles resembling catechin in appearance, soluble in alkalis with a yellow colour, and gave with lead acetate a yellow coloured precipitate, and with ferric chloride a purple-brown coloration. When heated in glycerol solution, or above its melting-point, aromadendrin gives kino yellow, a yellow resinous substance almost insoluble in cold water. It is, however, easily soluble in alcohol, and this solution possesses great staining power and dyes wool and skin a bright yellow colour.

Catechu or Cutch(CHAPTER XIV. Coumarane Group.)(Osa artikkelista)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

There are several varieties of catechu or cutch bearing different names according to the country or plants from which they are obtained. The following are those principally employed by dyers and tanners: Gambier catechu, Bengal or Acacia catechu, Bombay or Areca catechu, and Mangrove cutch.

Although catechu has perhaps received greater attention than other natural dyes, the results have been so varied that the chemistry of the subject was until recently in a most unsatisfactory condition. Some confusion has arisen from the non-appreciation of the fact that the main constituents of gambier and Acacia catechu are not identical, and some uncertainty has also apparently existed as to the botanical origin of the commercial varieties. Bombay catechu is, for instance, occasionally referred to as originating from the Acacia catechu, and Bengal catechu from the Areca catechu (Linn.); and in many cases, at the present time, it is impossible to ascertain the botanical derivation of commercial brown cutch preparations.

Gambier catechu.
Gambier, yellow cutch, cubical cutch, cube gambier, or terra japonica, is obtained from the Uncaria gambier, an extensive scandent bush which is met with, both wild and cultivated, in Malacca, Penang, and Singapore. The catechu is isolated by extracting the leaves and twigs with hot water until the liquid becomes syrupy, the insoluble matter being removed from time to time by means of a strainer. On cooling, the pasty mass is cut into cubes with sides i inch in length and dried on bamboo trays.

Catechin, C₁₅H₁₄O₆, 4H₂O, the crystalline principle, was first described by Nees van Esenbeck (Annalen, 1832, 1, 243), was subsequently examined by Berzelius in 1837 (Jahres., 14, 235), and more recently by numerous chemists. To isolate catechin, Löwe (Zeitsch. anal. Chem., 13, 113) devised the following method: catechu is washed with cold water to remove catechutannic acid, well pressed, allowed to dry, and dissolved in hot acetic ester. The filtered solution is evaporated and the residue crystallised from hot water.

According to Perkin and Yoshitake (Chem. Soc. Trans., 1902, 81, 1162), a combination of this method and that of Berzelius (loc. cit.) gives good results.

The finely powdered catechu is extracted with i o times its weight of boiling ethyl acetate, the solution is evaporated, and the residue crystallised from 10 times its weight of water. The product is again dissolved in boiling water, and lead acetate solution added, drop by drop, until a coloured precipitate is no longer formed, and the filtrate is almost colourless; the latter, while hot, is treated with sulphuretted hydrogen, the lead sulphide removed, and the crystals, which separate on cooling, are collected, washed, and allowed to dry at the ordinary temperature. The substance is now practically colourless, and the yield greater than if the purification had been effected by frequent crystallisation from water.

The formulæ which have been assigned to catechin are very numerous, and it has only recently been shown by v. Kostanecki and Tambor (Ber., 1902, 35, 1867), and simultaneously by Perkin and Yoshitake (loc. cit.), that it is correctly represented as C₁₅H₁₄0, 4H₂O

Catechin forms colourless needles, and when crystallised from water the air-dry product melts at 96° (Clauser, Ber., 1903, 36, 101). After standing over sulphuric acid, it possesses the formula C₁₅H₁₄O₆, H₂O, and melts at 176-177°, and this is also the melting-point of the anhydrous substance. Catechin is readily soluble in boiling water and cold alcohol, and gives with lead acetate solution a colourless precipitate, and with ferric chloride a deep green liquid. With pine wood and hydrochloric acid, it gives the phloroglucinol reaction.

On fusion with alkali, protocatechuic acid, phlorogucinol, and probably acetic acid are produced, and it is interesting to note that catechu has been considerably employed for the commercial preparation of the former compound.

[---]

Catechutannic acid.

In addition to catechin, gambier catechu contains a small amount of catechutannic acid, and this substance is present in considerable quantity in the browner varieties of cutch. To isolate it the following method has been employed:

A hot aqueous extract of catechu is allowed to stand until no more catechin is deposited, and the clear liquid is evaporated to dryness. The residue is dissolved in alcohol, the solution treated with ether to precipitate impurities and then evaporated to dryness.

Catechutannic acid consists of an amorphous reddish-brown powder, readily soluble in water and alcohol, insoluble in ether. According to Löwe (Fr., 13, 121), it possesses the formula C₂₁H₁₈O₈, and gives a lead salt 3P?bO, 2C₂₁H₁₈O₈, but this most probably requires revision.

According to Etti (Annalen, 186, 332) catechutannic acid is an anhydride of catechin, and is derived from this substance by elimination of water. It is said to be produced when an aqueous solution of catechin is heated to 110 (Löwe, ibid.) 12, 285), or by boiling catechin with solutions of the alkali carbonates. Again, catechin is decomposed at its melting-point with evolution of water and formation of a product resembling catechutannic acid, and aqueous solutions of catechin on long standing become browncoloured with apparent formation of this compound. That the products obtained by these methods resemble catechutannic acid is certain, but the subject has not been fully investigated.

Catechutannic acid solution gives a precipitate with lead acetate, and also resembles catechin in giving a green coloration with ferric chloride, and the phloroglucinol reaction with pinewood and hydrochloric acid. It is a powerful tanning agent, and appears to differ but little from the so-called "catechol" tannins.

[---]

Catechin, though largely employed for tanning purposes, does not precipitate a gelatine solution, and is not itself a tannin matter. On the other hand, it is absorbed by the hide, and there gradually passes into catechutannic acid.

Dyeing Properties.

On cotton, catechu is largely used. for the production of the well-known "catechu brown," which is exceedingly fast to light, acid and alkaline solutions, and also to bleaching powder. To obtain this, cotton is steeped in a hot solution of catechu (1-2 per cent.) to which has been added about 6 per cent, of copper sulphate, reckoned on the weight of the catechu employed. The material is allowed to remain in the bath as it cools, and without washing is then treated in a warm or boiling second bath containing i or 2 grams of bichromate of potash per litre. According to Hummel and Brown (J. Soc. Chem. Ind., 1896, 15, 422), in this operation the copper sulphate probably converts the catechin into catechutannic acid, and this is subsequently oxidised to japonic acid by the action of the bichromate. The colour is apparently intensified by the formation of a basic copper chromate. Gambier catechu is also employed in dyeing compound shades with logwood, fustic, and alizarine in conjunction with bichrome, and with bismarck brown, magenta, etc. In the latter case catechu-tannin forms the mordant for the basic colour.

Wool may be dyed with catechu in a similar manner to cotton. In silk dyeing, catechu is largely used for weighting purposes. The silk is steeped in basic ferrous sulphate solution, then in potassium ferrocyanide and hydrochloric acid, which causes the production of prussian blue on the fibre. It is then worked in a strong solution of gambier to which stannous chloride solution has been added.

Bengal or Acacia Catechu.
Bengal catechu is derived from the Acacia catechu, a tree 15 to 20 feet high, which is common in most parts of India and Burma. To isolate the catechu which is present in the red heartwood, the tree is cut down while it is fullest of sap, and the internal portion is sawn into small sticks and extracted with boiling water. The liquid thus obtained is concentrated over a fire, and then allowed to evaporate spontaneously in shallow dishes. The extract thus obtained comes into the market as Pegu catechu, brown cutch, and brown catechu (Crookes, "Dyeing and Calico Printing").

A purer substance, kath, or the pale catechu of India, is prepared by suspending twigs in the hot concentrated extract and collecting the crystals which thus separate.

Acacatechin, C₁₅H₁₄O₆, 3H₂O, can be obtained from the acacia kath by methods identical with those which are employed for the isolation of catechin from gambier catechu. It melts at 204-205°, is somewhat more sparingly soluble in water than catechin, and when fused with alkali gives phloroglucinol and protocatechuic acid. The reactions of acacatechin and catechin, in so far as they have been observed, are identical, and there is no difference in the composition of their derivatives when prepared under similar conditions. On the other hand, the melting-points of the substances themselves, and also of their derivatives, differ widely, as is evident from the following table (Perkin and Yoshitake):
Penta-acetyl derivative... Acacatechin 158-160° Catechin 124-125°
Pentabenzoyl ... Acacatechin 181-183° Catechin 151-153°
Azobenzene ... Acacatechin 198-200° Catechin 193-195°
Tetramethyl ... Acacatechin 152-154° Catechin 144-146°
Acetyl ... Acacatechin 135-137° Catechin 92-93°

It appears certain, therefore, that catechin and acacatechin are isomerides, and it is possible that the latter may, on the basis of v. Kostanecki and Lampe's formula for catechin, be represented thus (Perkin, private communication): [KUVA PUUTTUU] a point which should not be difficult to determine.

Bombay or Areca Catechu.
This variety is obtained from the fruit of the Areca catechu or betel-nut palm, a tree which is common in tropical Asia. Though its chief constituent resembles catechutannic acid, catechin itself has not been isolated from this product. It possesses a bright chocolate and sometimes an orange-brown colour, and yields, on dyeing, very similar results to the ordinary cutches.

Mangrove cutch is obtained from the bark of the mangrove Ceriops candolleana, and is of somewhat recent employment. In its preparation it is preferable to extract the fresh bark, which is of a light colour internally, rather than the stored product which has become red, or is said to have "sweated ". The extract, on evaporation, becomes deep-red in colour, and the object of the manufacturer is to prevent this anhydride formation from going too far, otherwise a certain portion of the extract is rendered insoluble in water.

By fusion with alkali, it gives protocatechuic acid, but at present no catechin has been isolated from it (Perkin, private communication). When dissolved in sodium bicarbonate solution, acetic ester extracts an almost colourless tannin, which possesses the properties of a catechol tannin.

For many purposes, mangrove cutch is competing closely with the other varieties of catechu, and this competition will no doubt become keener, if its quality can be further improved.

Mahogany.
According to Caseneuve (Ber., 8, 828) mahogany wood contains a catechin. (See also under Rhubarb tannic acid, p. 449.)

Quebracho Colorado(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

The Quebracho Colorado are anacardinaceous trees belonging to the genus Quebrachia, growing in the northern part of the Argentine Republic, the wood of which constitutes the well-known tannin substance "quebracho". It is imported into this country in the form of logs and is employed for tanning, either in the chipped condition or in the form of extract. Their wood is extremely hard, as the name "quebracho" (axe-breaker) denotes, and its specific gravity varies from 1.27-1.38.

Jean (Bull. Soc. chim., 1880, 33, 6) found that it contained 15.7 per cent, of a tannic acid, not identical with that of oak bark or chestnut wood, whereas Procter ("Leather Manufacture," 1903, 269) estimates it to contain about 20 per cent, of a tannin yielding reds (phlobaphene), and containing catechol and phloroglucinol nuclei. This tannin is somewhat sparingly soluble in water and can only be used in weak liquors, but gives a firm reddish leather.

In order to isolate the tannin, Strauss and Geschwender (Zeitsch. angew. Chem., 1906, 19, 1121) extract the bark first with chloroform and then with alcohol. Addition of water to the alcoholic extract causes the separation of phlobaphenes, and from the clear liquid concentrated in a vacuum the tannin is precipitated by lead acetate, the lead salt being collected, suspended in water and decomposed with sulphuretted hydrogen. The resulting solution is evaporated to dryness, the residue dissolved in alcohol and poured into ether. Thus obtained it consists of a light flaky mass, which is hygroscopic and becomes sticky on -exposure to moist air.

According to Arata (Jean, Bull. Soc. chim., 1879, 306) quebracho tannin, C₂₆H₂₄O₁₀, gives catechol on dry distillation, with nitric acid oxalic and picric acids, by fusion with alkali phloroglucinol and protocatechuic acid, whereas, by the latter method, Nierenstein isolated also hydroquinone and resorcinol (Collegium, 1905, 65). According to the latter author, the quebracho Colorado probably contains three tannins. By treating a cold aqueous extract of the quebracho Colorado with bromine, Böttinger (Ber., 17, 1123) obtained a reddish-yellow compound containing 42.1-44.5 per cent, of bromine. Nierenstein, who isolated the tannin according to Trimble's method ("The Tannins "), treated the solution with lead acetate, filtered, and on adding bromine to the clear liquid obtained a precipitate of monobromoquebrachotannin, C₁₆H₁₄BrO₈, which consists of a cinnabar red powder, and on digestion with alcoholic potash gives isovanillic acid and monobromoquebrachylic acid needles, melting-point 119-120°.

Strauss and Geschwender (loc. cit.) consider that quebracho tannin is identical with malettotannin, and with the tannin from cinchona bark, and ascribe to it the formula [C₄₁H₄₄O₁₈(OMe)₂]₂. With a mixture of acetic anhydride and acetic acid an acetyl compound, (C₃₀H₂₂O₁₁Ac₆)₂, colourless powder, is produced, and a corresponding benzoyl derivative, (C₃₀H22O₁₁Bz₆)₂, can also be prepared.

Quebracho phlobaphene, on distillation with zinc-dust, yields anthracene (Nierenstein, Ber., 1907, 40, 4575).

According to Arnaudon the wood contains a colouring matter which gives a fine yellow dye, and this has been examined by Perkin and Gunnell (Chem. Soc. Trans., 1896, 69, 1304), and found to be identical with fisetin, the colouring matter of young fustic. This compound, which appears to exist in the wood as glucoside, gives on fusion with alkali protocatechuic acid and resorcinol, and may account for the appearance of the latter phenol among the hydrolytic products of the crude tannin itself. According to Perkin and Gunnell, when an extract of the quebracho colorado is digested with boiling dilute acid a small quantity of ellagic acid is obtained.

In addition to the tannins above described, the quebracho Colorado is the source of the so-called "quebracho resin," which collects as a thickened juice in the crevices of the tree. It has been examined by Arata (Chem. Soc. Abstr., 1878, 984), who states that it is easily soluble in alcohol or ethyl acetate, insoluble in benzene. By fusion with alkali it gives protocatechuic acid (?) and phloroglucin, and by the action of nitric acid, oxalic and picric acids are produced.

A considerable amount of the tannin contained by the quebracho colorado is of a sparingly soluble nature, and is deposited to some extent from a hot aqueous extract on cooling. This product may be rendered soluble by treatment with alkalis or alkaline sulphites, and a large quantity of the so-called "soluble" quebracho extracts are prepared by heating the material in closed vessels with bisulphites, sulphites, sulphides, or even caustic alkalis (Lepetit, Dollfus and Gansser, Eng. Pat., 1896, 8582; cf. Procter, "Leather Manufacture," 338).

Algarobilla(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Algarobilla consists of the pods of the Caesalpinia brevifolia of Chili. The tannin appears to consist principally of ellagitannin, and this lies in resinous particles loosely attached to the somewhat open framework of the fibre. It is one of the strongest tannin matters known, and contains on the average 45 per cent. In character it resembles divi-divi, its extract being somewhat liable to fermentation. It is very suitable for tanning and also for dyeing purposes.

Dividivi(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Divi-divi consists of the dried pods of the Caesalpinia coriaria (Willd.), a tree 20-30 feet high, found in the West Indies and Central America. The pods are about 3 inches long and j inch broad, are very thin, and frequently resemble in shape the letter S. From 40-45 per cent, of tannin is present, which consists of ellagitannin and probably also a gallotannin. Extracts of this material have a somewhat unfortunate tendency to ferment, with simultaneous development of a deep-red colouring matter; but this can be prevented to some extent by the use of antiseptics. Divi-divi is largely imported for the preparation of leather, and is also employed for black dyeing, but its use is far more limited in this latter respect than myrobalans.

Valonia(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Valonia (Valonée, Fr.; Valonea, Ackcrdoppen, Orientalische Knoppern (Ger.)), an important tanning material, is the acorn cup of certain species of oak, usually Quercus aegilops (Linn.), and probably Q. macrolepsis, Q. graeca, Q. ungeri, and Q. coccifera (Linn). The former is most prolific in the highlands of Morea, Roumelia, Greek Archipelago, Asia Minor, and Palestine, whereas the Q. macrolepsis forms great forests in Greece. These acorn cups have a diameter up to about 1½ inches, and in good condition possess a bright colour.

The fruit ripens in Asia Minor about July or August, and the trees are then shaken, and the material left on the ground to dry; this is subsequently collected into heaps, and allowed to ferment for some weeks, until the acorn contracts and falls from the cup. The acorn, which contains but little tannin, is employed for feeding purposes.

In Greece distinct qualities of valonia are known, the best (chamada) collected about April before the fruit is ripe, a second (rhabdisto) in September or October, and a third little-used inferior variety (charcala).

Smyrna valonia may contain 40 per cent., Greek 19-30, and Candia valonia 41 percent, of tannin matter, which consists of a mixture of a gallotannin and an ellagitannin. Valonia is, indeed, an excellent source for the preparation of ellagic acid, because it so readily yields a product easy to purify. Extract of valonia frequently undergoes fermentation with deposition of ellagic acid, and to avoid this the employment of antiseptics is to be recommended.

Valonia is especially suited for the manufacture of sole leather, and together with gambier and other materials for dressing leather, but is little employed for dyeing purposes (cf. Procter, "Principles of Leather Manufacture," 259).

Myrobalans(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

This very important tanning material consists of the fruit or nuts of the Terminalia chebula, a tree of from 40-50 feet high, which grows in China and the East Indies. These nuts, which resemble a somewhat shrivelled plum, contain from 30-40 per cent, of tannin, the unripe fruit containing the largest amount. They should be bright in colour, and not soft, and require to be kept in a dry place, otherwise they absorb moisture and are then difficult to grind. The tannin present consists of a gallotannin, which is at least in part chebulinic acid, together with a fairly large amount of ellagitannin, and this, owing to fermentation and other causes, is decomposed to some extent during lixiviation into ellagic acid. Myrobalans from the dyer's point of view is one of the most serviceable tannin materials at the present time. Enormous quantities of its extract, especially as purified or decolorised extracts, are manufactured, and these are employed for cotton dyeing, in the black dyeing of silk, and in tanning.

Sumach(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

True sumach consists of the dried and usually powdered leaves of the genus Rhus (order Terebinthacæ], and is useful for tanning the finer kinds of leather, and also in dyeing and calico printing on account of the tannin matter present in it.

Sicilian sumach, the variety most esteemed in this country and throughout Europe, consists of the leaves of the Rhus coriaria (Linn.), a shrubby bush cultivated to a large extent in Sicily, where the sumach industry is of considerable importance. When the plant is about to flower the younger twigs are removed, dried in the sun, and subsequently beaten to remove the leaves and flower panicles. The sumach is imported sometimes in leaves, but more often in the form of powder, and should contain about 25 per cent, of tannin, although as much as from 27-32 per cent, may occasionally be found.

According to Löwe (Zeitsch. anal. Chem., 12, 128), the tannin matter present, C₁₄H₁₀O₉, is ordinary gallotannin; indeed it is well known that when an aqueous extract of the sumach is boiled with dilute sulphuric acid, considerable quantities of gallic acid are produced. On the other hand, Strauss and Geschwender (Zeitsch. angew. Chem., 1906, 1121), who isolated the tannin according to Löwe's instructions, detected the presence of a methoxy group, and suggest the formula C₃₂H₂₉O₁₁.OMe.

Sicilian sumach contains also a trace of an ellagitannin and myricetin, C₁₆H₁₀O₈, to the extent of about 0,1173 per cent. (Perkin and Allen, Chem. Soc. Trans., 1896, 69, 1299), the latter colouring matter having been previously mistaken by Löwe (Zeitsch. anal. Chem., 1874, 12, 127) for quercetin.

Considerable quantities of sand and sometimes particles of magnetic iron ore, which cause black stains, are often to be found in sumach (Procter, "Principles of Leather Manufacture," 1903, 271); (compare also Trotman, J. Soc. Chem. Ind., 1904); and it is frequently highly adulterated in the ground condition with the leaves and twigs of various plants. Of these, the Pistacia lentiscus (Linn.) ("schinia" or "skens"), Coriaria myrtifolia (Linn.), (French sumach or "stinco"), Tamarix africana (Poir.) (brusca), Tamarix gallica (Linn.), Ailanthus glandulosa (Desf.), Ficus carica (Linn.), Vitis vinifera (Linn.), other species of the Rhus family and also the ground branches ("gambuzza," "gammuzza") of the Rhus coriaria itself, are known to be employed. These sumach adulterants also contain tannin matters, but for tanning and dyeing purposes are as a rule much inferior to sumach itself.

The Pistacia lentiscus (Linn.), (mastic tree), a small tree about 20 feet high with evergreen leaves, grows abundantly in Cyprus. The leaves of this plant constitute the most important sumach adulterant, and about 10,000 tons are said to be exported from Tunis to Sicily annually and re-exported thence (as sumach?). According to Procter (loc. cit.) the leaves contain 12-19 per cent, of a catechol tannin. A good plump leather can be obtained from this material, but of a faintly reddish tint, the result being intermediate in character between those which are given by oak bark and sumach. Its presence in sumach is to be deprecated, and in many cases leads to injurious results. A considerable quantity, however, is consumed at Lyons in France as an assistant dyeing material for silk stuffs.

According to Perkin and Wood (Chem. Soc. Trans., 1898, 73, 374), these leaves contain a tannin closely allied to, if not identical with, ordinary gallotannic acid, as when an aqueous extract is boiled with dilute sulphuric acid a considerable quantity of gallic acid is produced. A second tannin or tannin glucoside is also present which, although possessing the general characteristics of the socalled "catechol" tannins in that it yields a red phlobaphene, and as noted by Procter, a reddish-coloured leather, gives, by fusion with alkali, gallic acid and phloroglucinol.

In addition to these tannins, myricetin (probably as glucoside) C₁₅H₁₀O₈ is also present to the extent of about 0,15 per cent.

Tamarix africana (Poir.) is a small shrub or tree characterised by its twiggy branches and minute scale-like leaves. The small twigs are collected in Tunis and imported into Sicily for the adulteration of sumach (Procter).

According to Perkin and Wood (loc. cit.} the leaves contain a tannin probably identical with gallotannin, in addition to a small quantity of an ellagitannin. A trace of yellow colouring matter is also present and consists of a quercetin methylether, C₁₆H₁₂O₇.

The Tamarix gallica (Linn.) closely resembles in appearance the Tamarix africana and flourishes in Cyprus, where the latter is not found. According to Procter, it contains 8,4 per cent, of tannin matter.

Ailanthus glandulosa (Desf.) is a tree of large size and handsome appearance, native of India and China, but common on the Continent. The leaves contain 11,2 per cent, of tannin matter (Procter), and this resembles gallotannin, although a trace of an ellagitannin is also present (Perkin and Wood). Curiously enough, although so high a percentage of tannin is present, leather is scarcely tanned by an extract of these leaves, but is merely stained a dull dirty colour. This material is therefore of little use for tanning purposes, and as an adulterant of sumach exerts a deleterious influence. A small quantity of quercetin can be isolated from the leaves.

The leaves of the Ficus carica (Linn.) (common fig tree) contain 1,6 per cent, of tannin (Procter) and a trace of a yellow colouring matter (Perkin and Wood). Skin is untanned by an extract of these leaves, but acquires, during the process, a dirty olive tint.

Gambuzza consists of the small stalks branching from the main root of the Rhus coriaria (Linn.), which are ground to powder and mixed with sumach. The material contains some quantity of a tannin resembling gallotannin, together with a trace of myricetin.

Attempts to detect the presence of these adulterants in sumach by chemical methods have not given satisfactory results, but should a prolonged boiling of the extract with dilute sulphuric acid cause the gradual precipitation of phlobaphene, the presence of the leaves of the Pistacia lentiscus may be suspected.

More satisfactory results can be obtained by microscopical examination, and an elaborate work on this subject has been carried out by Andreasch ("Sicilianischer Sumach und seiner Verfalschung," Wien, 1898); the book, however, is unsuitable for abstraction. A useful method, now generally adopted by leather trades chemists, has been devised by Lamb and Harrison (J. Soc, Dyers, 1899, 14, 60), and is based upon the behaviour of the leaf mixture with warm nitric acid. Under such treatment, the more delicate leaf structure of sumach itself is completely destroyed, whereas the strong cuticles of Pistachia lentiscus, Coriaria myrtifolia, Tamarix africana, and Ailanthus glandulosa, are unaffected and can then be readily recognised (compare also Lamb, ibul. t 1904, 20, 265). Again, the leaves of the R. coriaria are very easily distinguished from those of other plants employed for their adulteration, in that both upper and lower cuticles are covered with a dense growth of hairs (Priestman, J. Soc. Chem. Ind., 1905, 24, 231).

Venetian sumach or Turkish sumach consists of the leaves of the Rhus cotinus (Linn.), a small tree, the wood of which constitutes the yellow dyestuff known as "Young Fustic". The material contains about 17 per cent, of tannin, which resembles ordinary gallotannin, together with a trace of an ellagitannin. The presence of myricetin, C₁₅H₄O₂(OH)₆, in these leaves is interesting, in view of the fact that in the wood itself, fisetin, C₁₅H₆O₂(OH)₄, is present (Perkin, Chem. Soc. Trans., 1898, 73, 1016).

American sumach. The leaves of numerous varieties of Rhus are employed in the United States for tanning and dyeing purposes, and of these the R. glabra (Linn.) very largely takes the place of Sicilian sumach. It contains about 25 per cent, of a tannin closely resembling gallotannin, but produces a leather of very much darker colour than the Sicilian product.

Of the other varieties, R. typhina (Linn.) or "Virginian sumach" (10-18 per cent.), R. cotinoides (Nutt.) (21 per cent.), R. semialata (Murr.) (5 per cent), R. aromatica (Ait.) (13 per cent.) (Procter), R. metopium (Linn.) (about 8-2 per cent, of tannin, probably gallotannin, together with traces of both quercetin and myricetin), (Perkin, Chem. Soc. Trans., 1900, 77, 427), R. copallina (Linn.), R. pumila (Michx.), and R, toxicodendron (Linn.), are to be found in the States. Among these, R. glabra and R. copallina are considered to be worthy of extended cultivation.

In India, numerous species of the genus Rhus are known to exist (Watt's Dictionary, "Economic Products of India "), and again in Algeria the R. pentaphylla (Desf.) is used by the Arabs for tanning goat-skins. Finally, the Anaphrenium argenteum (E. Mey), (R. thunbergii). (Cape of Good Hope), 28 per cent, of tannin (bark), probably of the catechol class (Procter), and the Rhodosphaera rhodanthema (Engl.) (Rhus rhodanthema) (New South Wales), 9-5 per cent, of tannin (leaves), resembling gallotannin, are worthy of mention. The latter plant, also known as the "yellow cedar," closely resembles the R. cotinus, and it is interesting to note that although the wood of this tree contains fisetin, C₁₅H₄O₂OH)₄ the colouring matter of the leaves is quercetin, C₁₅H₃O₂(OH)₆ (Perkin Chem. Soc. Trans., 1898, 73, 1017).

French sumach is derived from the Coriaria myrtifolia (Linn.), a low deciduous shrub, native of Southern Europe, and has been referred to above as an adulterant of Silician sumach. In addition to tannin (15,6 per cent., Procter), which consists probably of ordinary gallotannin together with a little ellagitannin, it contains the poisonous glucoside coriamyrtin (Riban, Chem. Zeit, 1867, 663) and a trace of quercetin (Perkin, Chem. Soc. Trans., 1900, 77, 428). According to Procter, the colour of leather tanned by these leaves is very satisfactory and practically equal to that produced by genuine sumach (R. coriaria). It is also employed in black dyeing.

Cape sumach consists of the leaves of the Colpoon compressum (Berg.) (Osyris compressa, Fusanus compressus, Thesium colpoon), and is much used in South Africa under the name of "Pruimbast". The bush is found in the mountains, where it grows to the height of about 6 feet, and only the younger leaves are gathered. These leaves contain about 23 per cent, of tannin (Procter), which has been isolated as a hygroscopic transparent glassy mass and is probably a phlobatannin glucoside. With boiling dilute acid, a reddishbrown phlobaphene gradually separates, and on fusion with alkali protocatechuic acid is produced (Perkin, Chem. Soc. Trans., 1897, 71, 1135). In addition to tannin there is also present a considerable quantity of the quercetin glucoside Rutin (Osyritrin) (Chem. Soc. Trans., 1910, 98, 1776). According to Procter, this material forms a useful substitute for Sicilian sumach.

In lieu of the Colpoon compressum, a tanning agent known as "broach leaves" (botanical origin lacking) appears to be considerably employed in South Africa. It contains about 19,9 per cent, of tannin of the so-called "catechol" variety, together with traces of both quercetin and myricetin (Chem. Soc. Trans., 1898, 73, 384).

Russian sumach consists of the leaves of the Arctostaphylos uvaursi (Spreng.) (Bearberry), and is said to contain about 14 per cent, of tannin, which, according to Perkin (Chem. Soc. Trans., 1900, 77, 424), consists of a gallotannin together with traces of an ellagitannin. Minute amounts of both quercetin and myricetin have been isolated from this material.

Considerable quantities of "sumach extract" are now manufactured for dyeing and tanning purposes from genuine Sicilian sumach, and this is usually found on the market as a brown treacly liquid of about 52° Tw. So-called decolorised extracts are also prepared to compete with ordinary tannic acid, and for this purpose the addition of blood albumen to the dilute extract at about 48°, then raising the temperature to 70°, and subsequently filter-pressing, gives the most satisfactory results. Sulphurous acid again is employed to brighten the colour of extracts, and acts partly as a weak acid in decomposing the inorganic salts of the tannin or colouring matter and partly as a reducing agent. In this case it is usual to pass sulphur dioxide through the liquor before concentration (Procter).

Chestnut Extract.(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

The wood of the Spanish chestnut, Castanea vesca, though it contains only 3-6 per cent, of tannin, is the source of the much-valued chestnut extract. The bark contains more tannin than the wood (17 per cent), but is not much used. The tree, which grows to from 60 to 80 feet in height, is abundant in Italy, the South of France, and Corsica, where it forms immense forests, and it is also very common in America.

Trimble ("The Tannins"), who very carefully examined the tannin, obtained analytical data and reactions which indicated that it was identical, or nearly so, with gallotannin, but it is probable that this wood also contains traces of a catechol tannin, for a certain quantity of a red colouring matter is also present, which resembles in character a phlobaphene. Some writers have suggested that chestnut tannin is a methyl ether of ordinary gallotannin, but there is apparently no definite evidence in support of this theory.

Chestnut is employed almost entirely in the form of extract, the strength of which varies, but usually contains from 26 to 32 per cent, of tannin. The extract is frequently decolorised, and some times mixed with quebracho extract and other materials. Chestnut tannin is the tannin which is most largely employed for the dyeing of silk. Castanea vesca appears to be frequently confused with the horse-chestnut, Æsculus hippocastanum. The tannin derived from this latter is, however, of little or no practical value.

Gall Nuts.(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

These are morbid excrescences produced by the puncture of an insect called Cynips gallæ-tinctoria upon the leaves and young twigs of certain kinds of oak trees, more especially those of Quercus infectoria (Oliver), Q. lusitanica (Lam.), growing in the East Indies, Persia, the Levant. If the fully developed nut be broken open it will be seen to contain a central cavity, in which the larva of the insect will be found. As a rule the galls are collected before the larvae are fully developed, and therefore before they have perforated the galls and escaped as mature insects. In this condition they contain the most tannic acid and are known as blue, black, or true nuts. The less valuable or perforated variety are larger and paler in colour and are known as white or false nuts.

Aleppo galls are one of the best varieties on the market, and should contain from 50-60 per cent, of tannic acid. This same oak, the Quercus infectoria, also bears a large gall known as the Apple of Sodom, due to a different insect, which contains from 24-34 per cent, of tannin and has been used for tanning purposes.

Other varieties are Smyrna galls, Austrian, and Hungarian galls, and of these the former are considered best. English oaks yield several species of galls and oak apples, which, however, are not of much value.

Chinese galls are produced by the action of an insect termed the Aphis chinensis on a species of sumach, Rhus semilata. These are hollow and possess very thin walls, but are much larger and more irregular in shape than the ordinary Aleppo variety, moreover, when freshly gathered, they are covered with a very fine down. They are much esteemed owing to their richness in tannin matter, of which frequently as much as 70 per cent, is present. On this account they are largely employed for the manufacture of tannic acid.

Gall-nut extract is employed for mordanting purposes when very delicate shades are required. In addition to tannic acid, all varieties of gall-nuts appear to contain minute traces of ellagitannic acid.

Group III. Catechol or Phloratannins.(CHAPTER XIII. Tannins.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

The catechol tannins are characterised among other distinctive features by the important fact that when digested with boiling dilute mineral acids a red precipitate, known as "anhydride" or "phlobaphene," is produced. The designation "catechol" arises from the fact that the majority of these substances give a green coloration with ferric chloride, and protocatechuic acid or catechol as one of their decomposition products. Such a classification is, however, misleading, in that by comparison with gallotannin, one is led to infer that these substances are similarly constituted and derived from diprotocatechuic acid only (OH)₂C₆H₃.CO.O.C₆H₃(OH)COOH

When hydrolysed, however, diprotocatechuic acid gives two molecules of protocatechuic acid without production of phlobaphene (Emil Fischer, private communication). Moreover, certain phlobaphene- yielding compounds are now known to exist in which a catechol nucleus is absent. Thus the cyanomaclurin of Jakwood (q.v.) is an instance in point, for although it contains only phloroglucinol and resorcinol nuclei, it readily yields a red anhydride of this character (cf. also Mimosa tannin, Pistachia tannin, and Maletto tannin). Evidently therefore the phlobaphene reaction is either due to the special structure of the tannin itself, or to the presence of a second phenolic grouping other than catechol in the molecule. This structure may perhaps vary in certain cases, but until this is clear it appears to be preferable to include all phlobatannins under one group rather than to complicate the subject by the introduction of subdivisions.

Bottinger and Etti (loc. cit.} have suggested a benzophenone structure for certain tannins, and this applied to the phlobatannins has, at first sight, the merit that maclurin (see Old Fustic) with dilute hydrochloric acid gives rufimoric acid (Wagner, Jahres., 1851, 420), a red amorphous phlobaphene-like mass. Kinoin (see Kino), usually regarded as the methyl ether of a pentahydroxybenzophenone, is readily transformed into kino-red, whereas aromadendrin (see Kino), apparently also a benzophenone derivative, resembles, according to Maiden and Smith, catechin in many of its properties. It has not yet been ascertained if the carboxylic acids of certain hydroxybenzophenones are tannins, but on the other hand it is to be remembered that compounds possessing such a structure will be strong mordant dye-stuffs, a property which is generally absent from tannins of the so-called catechol type. As already indicated, many phlobatannins are known which contain two distinct nuclei, more frequently phloroglucinol in addition to catechol, a fact which in these cases accounts for their reactivity with diazobenzene. More difficult to understand, however, is the precipitation of all phlobatannins in aqueous solution with bromine; this could be accounted for in those instances in which phloroglucinol or resorcinol nuclei are present in the compound, but curiously enough no difference in this respect appears to have been observed in cases where evidence as to the existence of these latter groupings has been of a negative character. Though by incautious alkali fusion, the existing phloroglucinol nucleus may escape detection and probably in many instances has done so, this evidence is such that it is hard to presume that in all cases bromine precipitation arises from the presence in these compounds of a specific phenolic grouping.

It is most probable that the phlobaphene reaction is, in many cases, to be assigned to the well-known reactivity of the phloroglucinol group present in these substances, and this has also been suggested by Emil Fischer. Thus coloured compounds can be obtained by the interaction of phloroglucinol with many aldehydes, of which the red phloroglucinol vanillein is an example, and moreover the phloroglucides of Counder (Ber., 1895, 28, 26), prepared by passing hydrogen chloride into mixtures of phloroglucinol and various sugars in aqueous solution, are coloured, the d-galactose phloroglucide possessing a red tint. Again, by boiling dextrose and phloroglucinol with dilute hydrochloric acid, a brownish-red precipitate of a phlobaphene-like character can be easily produced (private communication). Interesting in this respect also is the "phlorotanninred" of Schiff (Annalen, 245, 40), which he obtained by heating his so-called diphloroglucinol carboxylic acid to 160-175°.

That phlobatannins like gallotannin owe their tanning property, as a rule, to the depside grouping appears likely, and it has indeed been observed by Trimble ("The Tannins," ii., 91) that tannins from various species of oak, on long digestion with boiling 2 per cent. hydrochloric acid, give not only phlobaphene but some quantity of protocatechuic acid.

In the light of the researches of E. Fischer and Freudenberg (loc. cit.), it is also to be anticipated that many of these compounds will be eventually found to possess a sugar nucleus.

Closely connected with the phlobatannin group are the welldefined crystalline substances catechin, aca-catechin and cyanomaclurin, to the first of which the constitution has been assigned by v. Kostanecki and Lampe.

Catechin, although not a tannin, reacts with pine wood and hydrochloric acid, gives with bromine water the insoluble bromcatechuretin and readily yields substances of a phlobaphene character. Though the evidence is not precise it is stated by Loewe and also by Etti that catechin can be readily transformed into catechutannic acid, a substance existing side by side with it in the plant and possessing properties typical of the phlobatannin group. It has indeed been surmised that the catechol tannins of certain plants may owe their origin to the prior existence of substances of the catechin type, and that in addition to the compounds previously enumerated, the so-called quebracho resin and guarana catechin are intermediate products of tannin formation. Again, according to Procter (private communication), a colourless catechin-like substance is to be found in mangrove cutch.

With the exception of coca-tannic acid, no crystalline catechol tannins have been described, but all are amorphous and very similar in appearance to natural gallotannin, although on keeping, especially in the moist condition, they are apt to develop a red tint. According to Perkin, most phlobatannins can be prepared in a nearly colourless condition by extracting a solution of the crude tannin to which sodium bicarbonate has been added with ethyl acetate (cf. Gallotannin).

Numerous phlobatannins have been isolated, and a description of them is given below, although it is extremely doubtful whether the majority of these are individuals. In many cases, indeed, the general reactions of these compounds are the same, and considering the extreme difficulty in the effective purification of amorphous preparations of this character, specific differences which have been observed will no doubt, on further investigation, largely disappear. Trimble (loc. cit., ii., 132), who submitted certain phlobatannins to careful purification, found that there was a fair approximation in their percentage compositions, and it is thus natural to presume that the known members of this group are not so numerous as was formerly considered to be the case.

Anachueta wood and bark contain a tannin which gives a green coloration with iron salts.

Aspertannic acid, C₁₄H₁₆O₈, was obtained by Schwarz from Woodruff (Asperula odorata, Linn.), and gives a green colour with ferric salts. It does not yield precipitates with albumen, gelatin, and tartar emetic solutions.

Atherospermatannin, from the bark of Atherosperma moschatum (Labill.), gives a green colour with ferric salts. A lead salt, C₁₀H₁₄PbO₃, has been described by Zeyer (Jahrb. Min., 1861, 769).

Barbitamao tannic acid, from the bark of the Stryphnodendron barbatimum (Mart), (Wilbuszwitcz, Ber. Ref., 1886, 19, 349), is an amorphous red powder, which yields a phlobaphene, and on fusion with alkali, protocatechuic acid and phloroglucinol.

Beech tannin, from the bark of the red beech, contains a tannin of the composition C₂₀H₂₂O₉ (Etti, Monatsh., 10, 650).

Caffetannic acid, C₁₅H₁₈O₉, occurs in coffee berries in the form of calcium and magnesium salts (Rochleder, Annalen, 59, 300); in cainia root, Chiococca brachiata (Ruiz, et Pav.), (Rochleder and Hlasiwetz, ibid., 1848, 66, 35); Nux vomica (Sander, Arch. Pharm., 1897, 235, 133); St. Ignatius beans (ibid.}, and Paraguay tea, Ilex paraguensis (A. St. Hill.), (Rochleder, Annalen, 1847, 66, 39), (cf. also Graham, Stenhouse and Campbell, J. pr. Chem., 1856, 69, 815; Arata, Ber., 1881, 14, 2251; Kunz-Krause, Arch. Pharm., 1893, 231, 613; Ber., 1897, 30, 1617).

It is an amorphous powder readily soluble in water, gives a darkgreen coloration with ferric chloride, and when boiled with potassium hydroxide solution gives caffeic acid and a sugar (Hlasiwetz, Annalen, 1866, 142, 220), which is glucose (Sander, loc. cit.). On dry distillation catechol is formed, and by fusion with alkali protocatechuic acid is obtained. The ammoniacal solution becomes green on exposure to air with formation of viridic acid, a substance which is also present in coffee berries in the form of its calcium salt (Rochleder, Annalen, 63, 197). According to Griebel (Inaugural Diss. Munich, 1903) caffetannic acid is C₁₈H₂₄O₁₀, and a penta-acetyl derivative corresponding to this formula is described.

Callutannic acid, C₁₄H₁₄O₉, contained in heather, Calluna vulgaris (Salisb.), is an amber-coloured substance. It gives a green coloration with ferric chloride, and when heated with dilute mineral acids yields an amorphous anhydro derivative, C₁₄H₁₀O₇ (Rochleder, Annalen, 84, 354; Sitz. Ber., 9, 286).

Canaigre tannin is present in the tuberous roots of the Rumex hymenosepalus (Torr.), an important American tanning material. It has been submitted to an elaborate examination by Trimble ("The Tannins," 1894, ii., 115), who describes it as a yellowish-white powder readily soluble in water, which gives with lead acetate solution a yellow precipitate, and with ferric chloride a green precipitate. It reacts with bromine water to give a yellow deposit, and on heating to 160-190° is decomposed with production of catechol. Boiling 2 per cent, hydrochloric acid yields an insoluble red phlobaphene together with some protocatechuic acid. Sugar is not formed in this decomposition. Analysis gave C = 58,10; H = 5,33, figures which approximate to, though they are somewhat lower than, those given by the best-known phlobatannins.

Catechutannic acid (see Catechu).

Cherry bark tannin, C₂₁H₂₀O₁₀+½H₂O, is present in the bark of the Prunus cerasus (Linn.), (Rochleder, Sitz. Ber., 59, 819), and gives a green coloration with ferric chloride. It is not a glucoside, but when digested with boiling dilute acids gives a red phlobaphene, C₂₁H₁₆O₈+¾H₂0.

Cocatannic acid, C₁₇H₂₂O₁₀+2H₂O (?), present in the leaves of the Erythroxylon coca (Linn.), (Niemann, Jahrb. Min., 1860, 386), is sparingly soluble in cold water and gives a green coloration with ferric salts. According to Warden (Pharm. J., 18, 985) it can be obtained in microscopic crystals of a sulphur yellow colour.

Colatannin or Kolatannin, C₁₆H₂₀O₈, a light red amorphous powder, exists in the Kola nut, Cola acuminata (Schott and Endl.), in combination probably with caffeine and theobromine (Knox and Prescott, Amer. Chem. J., 1897, 19, 63). With ferric acetate it gives a green coloration, and on fusion with alkali protocatechuic acid is obtained. Penta-acetylkolatannin, C₁₆H₁₅O₈(C₂H₃O)₅, colourless powder, tribromkolatannin, C₁₆H₁₇O₈Br₃, red-brown powder, penta-acetyl-tribromkolatannin, C₁₆H₁₂O₈Br₃(C₂H₃O)₅, pentabrom, and hexabromkolatannin have been described. On heating, kolatannin yields various anhydrides, (C₁₆H₁₉O₇)₂O at 107-110°, (C₁₆H₁₇O₆)₂O at 135-140°, and C₁₆H₁₆O₆ at 155-156°.

Cortepinitannic acid, C₃₂H₂₄O₁₇, occurs together with pinicortannic acid in the bark of the Scotch fir, Pinus sylvestris (Linn.), It consists of a bright red powder, the aqueous solution of which gives an intense green coloration with ferric chloride (Kawalier, Sitz. Ber., 11, 363).

Euphrasia tannin is present according to Enz (Vierteljahrsch. Pharm. J., 8, 175) in the green parts of Euphrasia officinalis (Linn.), and gives a green colour reaction with ferric salts. Its lead salt has the composition C₃₂H₂₀Pb₃O₂₀.

Fragarianin, v. Strawberry tannin.

Filitannic acid, C₄₁H₃₆NO₁₈ (?), exists in fern-root (Aspidium filix mas, Swartz.), (Malin, Annalen, 143, 276), and forms a red-brown powder which, in aqueous solution, gives an olive-green coloration with ferric chloride. By boiling with dilute sulphuric acid it gives filix red, C₂₀H₁₈O₁₂, an amorphous compound, and this when fused with alkali gives phloroglucinol and protocatechuic acid (cf. also Reich, Arch. Pharm., 1900, 238, 648).

Fraxitannic acid, C₂₆H₃₂OH (?) occurs in the leaves of the as tree, Fraxinus excelsior (Linn.). It consists of a brownish-yellow deliquescent powder, and when heated at 100° loses water and forms an almost insoluble anhydride, C₂₆H₃₀O₁₃ (Gintl and Reinitzer, Monatsh., 3, 745). Aqueous ferric chloride produces a dark green coloration, and when oxidised with permanganate this tannin yields quinone. Acetylfraxitannic acid, C₂₆H₂₈O₁₄(C₂H₃O)₄, benzoylfraxitannic acid, C₂₆H₂₈O₁₄(C₇H₅O)₄, tribromfraxitannic acid, c₂₆H₂₉Br₃O₁₄, and tetra-acetyltribromfraxitannic acid, C₂₆H₂₅Br₃O₁₄(C₂H₃O)₄, have been described.

Galitannic acid, C₁₄H₁₆O₁₀, H₂O, exists in the bark of the Galium verum (Linn.), (Schwarz, Annalen, 83, 57). It gives a yellow precipitate with basic lead acetate and a green colour reaction with ferric chloride.

Guarana tannin is present in the Paullinia cupana (H. B. and K.), the seeds of which, known as "guarana," contain theine and are extensively used in South America for medicinal purposes. According to Nierenstein (Die Gerbstoffe, 20) the tannin consists of small colourless crystals, melting-point 199-201°, and yields an acetyl derivative, melting-point 134-136°. It is laevo-rotatory, having [a]_D²⁰=72,4° in water, and [[a]_D²⁰=-39,1° in alcohol.

Hemlock tannin, C₂₀H₁₈O₁₀ (?) is present in Hemlock bark, Tsuga [Abies] canadensis (Carr.), the extract of which is prepared on a very large scale in North America for tanning purposes. According to Bottinger (Ber., 1884, 17, 1125), it is probably related to the quercitannic acid of the oak, and on heating with sulphuric or hydrochloric acid gives the anhydride hemlock red, C₄₀H₃₀O₁₇. With hydrochloric acid at 180, hemlock red evolves methyl chloride; when heated with acetic anhydride the acetyl compound is produced, whereas bromine gives a mixture of the compounds C₄₀H₂₀Br₁₀O₁₁ and C₄₀H₁₆Br₁₄O_i7. Bromine added to the diluted tannin extract precipitates tetrabromhemlock tannin, C₂₀H₁₄Br₄O₁₀, a yellow powder which yields the penta-acetyl derivative C₂₀H₉Br₄O₁₀(C₂H₃₀)₆, and by the further action of bromine the bromine compound C₂₀H₁₂Br₆O₁₀ (cf. Trimble, Amer. J. Pharm., 1897, 69, 354, 406; J, Soc. Chem. >Ind., 1898, 17, 558) is produced.

Hop tannin, C₂₂H₂₆O₉, present in hops (Humulus lupulus, Linn.), (Etti, Annalen, 180, 223; Monatsh., 10, 651), has all the properties of a catechol tannin. It gives with ferric chloride a dark green coloration and with boiling dilute mineral acid the phlobaphene "hop red," C₃₈H₂₆O₁₅. Hop red forms a cinnamon-coloured powder and on fusion with potash yields phloroglucinol and protocatechuic acid.

Horse chestnut tannin, C₂₆H₂₄O₁₂, is present in nearly all parts of the Aesculus hippocastanum (Linn.) and in the root bark of the apple tree (Rochleder, Sitz. Ber., 53, [ii.], 478; 54, [ii.j, 609). It consists of a nearly colourless powder, the solution of which gives a green coloration with ferric chloride, and when boiled with dilute mineral acid the phlobaphene C₂₆H₂₂O₁₁ or C₂₆H₂₀O₁₀. On fusion with alkali, phloroglucinol and protocatechuic acid are produced. V. also phyllascitannin and CHESTNUT EXTRACT.

Ipecacuanhic acid, C₁₄H₁₈O₇, was obtained by Willigt (Annalen, 76, 345) from the roots of Psychotria ipecacuanha (Stokes), and consists of a reddish-brown, bitter hygroscopic substance. Its solution gives a green coloration with ferric chloride.

Japonic acid (see CATECHU).

Kino (see KINO).

Larch tannin. The bark of the larch, Larix europaea (DC.), contains considerable quantities of a tannin which was examined by Stenhouse (Phil. Mag., 23, 336). It forms an olive-green precipitate with ferric salts, and when boiled with dilute sulphuric acid a red phlobaphene is produced.

Maletto tannin occurs in the bark of Eucalyptus occidentalis (Endl.) and other species of eucalyptus. According to Strauss and Geschwender (Zeitsch. angew. Chem., 1906, 19, 1121) it possesses the formula (C₄₃H₅₀O₂₀)₂, and appears to be identical with quebracho tannin. Dekker (Arch. Neerland., 1909, ii., 14, 50) prefers the formula (C₁₉H₂₀O₉)_?, and describes the acetyl derivative C₃₈H₂₈O₁₆Ac₁₀ and benzoyl derivative C₁₉H₂₅O₁₂Bz₅. Heated with zinc-dust and sodium hydroxide solution the tannin gives small quantities of gallic acid and phloroglucinol, whereas dry distillation yields pyrogallol and traces of other phenols. Boiling dilute sulphuric acid forms "maletto red," C₅₇H₅₀O₂₂ from which the acetyl derivative can be obtained.

Mangrove tannin, C₂₄H₂₆O₁₂. This important tannin is derived from the Rhizophora mangle (Linn.), R. mucronata (Lam.), Ceriops candolleana (Arn.), C. roxburghiana (Arn.), and other allied species. It is described as an amorphous red powder, which on fusion with alkali gives protocatechuic acid, and with boiling dilute sulphuric acid the phlobaphene C₄₈H₄₆O₂₁. The monacetyl derivative C₂₄H₂₅O₂₃(C₂H₃O) melts at 205° (Nierenstein, Die Gerbstoffe). This tannin closely resembles in its properties catechutannic acid (see CATECHU), and indeed mangrove cutch and catechu may be employed in many cases for the same purpose. Possibly these two substances are identical, and Procter (private communication) has isolated from mangrove cutch a small quantity of a colourless crystalline substance resembling catechin. Perkin who examined an ethyl acetate extract of the fresh bark of the C. candolleana, prepared in Borneo, was unable to detect the presence of a catechin, but obtained the tannin as a pale yellow powder, which gave a green coloration with ferric chloride solution, and resembled catechutannic acid in many respects.

Mimosa tannin is derived from various species of Mimoseae, such as the Acacia arabica (Willd.) of Egypt, the so-called "Wattles" of Australia, and numerous others. The tannin present is interesting in that though it possesses the reactions of a phlobatannin, such as phlobaphene production, precipitation by bromine water and solubility of its lead compound in acetic acid, etc., it gives a bluish-violet coloration with ferric chloride. Ammonium sulphide gives a precipitate with a mimosa solution, when after removal of the excess by boiling, a few drops of sulphuric acid are added, followed by a small quantity of salt. All other phlobatannins, except Maletto and Pistaschia tannins, give no precipitate by this method (Stiansy, private communication).

Moritannic acid, see Maclurin.

Oxypinitannic acid, v. Pinitannic acid.

Oak bark tannin or Quercitannic acid is found in the bark of the oak, and is not to be confused with the tannin of oak-wood from which it is distinct, and which is described below under the name of quercinic acid. In 1792 George Swayne communicated to the Society of Arts his results on the use of oak leaves in tanning (Trimble, "The Tannins," ii., 51), and the subject was again discussed by Berzelius in his Lehrbuch, 1827, and by Liebig (Handbuch der Chemie, 1843). Assumed at that time to be identical with the tannin of nut-galls (gallotannin), it was first shown by Stenhouse (Phil. Mag., 22, 425) to differ from this substance. According to Grabowski (Sitz. Ber., 56, [ii.], 388), Oser (ibid., 72, [ii.], 178), Johanson (Arch. Pharm., [in.], 9, 210), Bd'ttinger (Ber., 14, 1598), quercitannic acid is in reality a glucoside, but Etti (Ber., 14, 1826; Monatsh., 4, 512) found that the pure substance did not yield a trace of sugar. Various formulæ have been assigned to this substance, viz. Eckert (Jahres., 1864, 608), C₂₈H₂₀O₂₀; Oser (Jahres., 1875, 600), C₂₀H₂₀O₁₁; Löwe (Zeitsch. anal. Chem., 20, 210), C₂₈H₃₀O₁₅; Bottinger (Ber., 1883, 16, 2712), C₁₅H₁₂O₉, 2H₂O, and Etti (Monatsh., 10, 650), C₁₇H₁₆O₉, C₁₈H₁₈O₉, and C₂₀H₂₀O₉.

Quercitannic acid is described by Etti as a reddish-white powder almost insoluble in water. One of its most characteristic properties is the readiness with which it forms reddish-brown anhydrides when heated by itself or with dilute acids. Thus at 130-140° the first anhydride, C₃₄H₃₀O₁₇, is produced, and this by heating with dilute sulphuric or hydrochloric acid gives the second anhydride, C₃₄H₂₈O₁₆, Boiling dilute sulphuric acid again converts the original tannin into the third anhydride, 2C₁₇H₁₆O₉ 3H₂O = C₃₄H₂₆O₁₅.

These compounds are insoluble in water, but colour a solution of ferric chloride blue (?). Löwe (loc. cit.) again examined an anhydride, C₂₈H₂₄O₁₂, and an "oak red," C₂₈H₂₂O₁₁. Bottinger, who prepared the oak red from the tannin by means of dilute sulphuric acid, adopted the formula (C₁₄H₁₀O₆)₂, H₂O. Etti (Ber., 1884, 17, 1823) isolated from the bark of the Quercus pubescens (Willd.) a tannin C₂₀H₂₀O₉, practically identical with the substance C₁₇H₁₆O₉ previously found in the Q. robur (Linn.), but giving a green solution with ferric chloride, and not a blue, as formerly stated.

When heated with dilute sulphuric acid at 130-140°, quercitannic acid gives in addition to anyhydride 1,5 per cent, of gallic acid, and with strong hydrochloric acid at 150-180° the formation of oak red was accompanied by the evolution of methyl chloride (Etti, Monatsh., 1, 274). On dry distillation it yields dimethylcatechol and catechol, and on fusion with alkali protocatechuic acid, catechol, and phloroglucinol.

By the action of bromine on the aqueous bark extract, Bottinger (Ber., 1883, 1 6, 2710) obtained dibromquercitannic acid, C₁₉H₁₄Br₂O₁₀, as a yellow precipitate, and from this penta-acetyldibromquercitannic acid was prepared. Heated with hydrochloric acid at 180°, methyl chloride was evolved, and by means of hydroxylamine hydrochloride the compound C₁₉H₁₅Br₂NO₁₀ was produced. Reduced with sodium amalgam hydroquercinic acid, C₁₅H₁₈O₇ or C₁₅H₁₆O₆, and hydroquergalic acid, C₁₄H₁₄O₆, are formed (Annalen, 263, 121). When suspended in chloroform and further brominated it yields tetrabromdehydroquerdtannic acid. Quercitannic acid was thus C₁₉H₁₆O₁₀, contained five hydroxyls, and the group COCH₈.

According to Etti (Monatsh., 10, 647) a further investigation of the tannins C₁₇H₁₆O₉ and C₂₀H₂₀O₉ has proved that they are not glucosides, but derivatives of a ketone acid, C₆H₂(OH)₃.CO.C₆H(OH)₃COOH

Trimble ("The Tannins," 1894, ii., 77) carried out an elaborate investigation of the tannins present in the barks of the Quercus alba (Linn.), Q. coccinea (Wangenh.), Q. discolor (Ait.), Q.falcata (Michx.), Q. palustris (Du Roi), Q. prinus (Linn.), Q. bicolor (Willd.), Q. obtusiloba (Michx.), Q.phellos (Linn.), Q. rubra (Linn.), Q. robur (Linn.), Q. semicarpifolia (Sm.), employing acetone for the purpose of extraction. The tannins in most cases had a pale yellow colour, gave with ferric chloride a green coloration, and practically identical results with all the usual tannin reagents.

Heated with glycerol at 160, the tannins of Q. tinctoria, Q. palustris, Q. falcata, and Q. phellos yielded catechol, whereas with fused alkali the eight samples examined gave protocatechuic acid. Though all these compounds produce a violet colour on pine wood moistened with hydrochloric acid, phloroglucinol or other phenol was not detected among their decomposition products. Heated with 2 per cent, hydrochloric acid for two and a half hours, a phlobaphene separated, whereas the solution contained protocatechuic acid. Analyses of nine of these tannin preparations showed but little variation, the average being C = 59,79; H = 5,08, and approximately correspond with those of Etti (loc. cit.) for the tannin C₂₀H₂₀O₉ from Q. pubescens, and of Kraemer (Amer. J. Pharm., 1890, 236) for the tannin of Q. alba.

Oak wood tannin, Quercin, Quercic acid, Quercinic acid, C₁₅H₁₂O₉, 2H₂O, consists of a light brownish-yellow substance, and is distinguished from the quercitannic acid of oak bark in that its aqueous solution gives a blue, not green, coloration with ferric chloride, and does not yield a precipitate with bromine water (Böttinger, Ber., 1887,20,761).

With the object of isolating the tannin in a pure condition, Bottinger acetylated a purified extract of the wood, and decomposed the acetyl compound C₁₅H₇(C₂H₃O)₅O₉ by heating it with water at 135°. By the action of sodium amalgam on the acetyl derivative, Böttinger (Annalen, 263, no) obtained hydroquercic acid, C₁₅H₁₈O₇ or C₁₅H₁₆O₆, querlactone, C₅H₆O₂, and an acid which is probably trihydroxybutyric acid.

Hydroquercic acid is a grey-brown, bitter hygroscopic powder, which forms the acetyl derivative C₁₅H₁₄(C₂H₃O)₂O₆, the barium salt (Cl5H15Ofl ) 2Ba, and the lead salt (C₁₅H₁₅O₆)₂Pb. Querlactone, on the other hand, forms the salt (C₅H₇O₃)₂Pb. As above noted, hydroquercinic acid could also be obtained in a similar manner from qiiercitannic acid.

Etti (Monatsh., 10, 647) isolated from the wood of the Slavonian oak a tannin C₁₆H₁₄O₉ which appeared to be a ketonic compound. This is present in the wood in the form of a readily soluble salt (probably magnesium salt). Crystallised from alcohol, it forms brownish-red microscopic warty spherical masses, insoluble in water, and having the properties of a monobasic acid (cf. Fuchs, Monatsh., 9, 1132). With phenylhydrazine it gives the compound C₂₂H₂₀N₂O₈, forms a brown amorphous oxime C₁₆H₁₅NO₉, and with dilute sulphuric acid at 120-130° yields gallic acid in addition to a red anhydride. Heated alone at 130-135°, or in a sealed tube with water at 100°, anhydrides are also produced, which on boiling with hydriodic acid evolve methyl iodide. On long digestion of the tannin C₁₆H₁₄O₉ with hydrochloric acid at 100°, a methoxyl group is split off, with production of a yellow coloured acid C₁₅H₁₂O₉ in which a methoxyl group is still present. This tannin is therefore probably the dimethyl ether of the ketonic acid formulated above.

On boiling the tannin with dilute sulphuric acid, the anhydride C₃₂H₂₄O₁₆ is produced, whilst on heating in a closed tube the anhydrides C₃₂H₂₀O₁₄ and C₃₂H₁₈O₁₃ were obtained.

The varied results of many of these workers with the oak tannins appear to be due, as suggested by Trimble, to the fact that in many cases they employed oak tannin extracts of doubtful authenticity. Thus it is possible that Etti, who in his earlier work describes the tannin as producing a blue coloration with ferric chloride, was in reality examining oak-wood and not oak-bark preparations, and again the peculiar insoluble property of certain of his tannins, also commented on by Trimble, suggests that in these cases he investigated an anhydride rather than the tannin itself. That oak barks contain a phlobatannin possessing a catechol nucleus appears to be certain from the investigations of Trimble, and it seems probable that in the wood either a pyrogallol tannin or a phlobatannin containing a pyrogallol group is present. Though, as stated above by Etti in the case of the Slavonian oak, this yields phlobaphenes, Stiasny (private communication) considers that such is not usually the property of oak-wood extracts. An interesting point, moreover, apparently not stated in the literature, though well known to tanners, is that oakwood extracts give some ellagic acid, and on this account impart to leather the "bloom" so characteristic of this substance.

Oenotannin, C₁₉H₁₆O₁₀ (?), was obtained by Gautier from red wine (Bull. Soc. chim., 1877, 27, 496), who describes it as a colourless substance readily soluble in water. It gives a green coloration with ferric chloride solution, by fusion with alkali protocatechuic acid and phloroglucin, and when exposed to moist air becomes converted into an insoluble red phlobaphene-like substance. According to Heise (Ber. Ref., 22, 823), oenotannin contains gallotannin and is a mixture of three compounds.

Pistachia tannin is present in the leaves of the Pistacia lentiscus (Linn.) in addition to some quantity of a gallotannin (Perkin and Wood, Chem. Soc. Trans., 1898, 73, 378), and consists of a pale brown brittle mass which with iron alum solution gives a blue-black coloration. With boiling dilute sulphuric acid a phlobaphene quickly separates, and when fused with alkali, gallic acid and phloroglucinol are produced.

Phyllœscitannin is the name given by Rochleder to a tannin present in the small leaflets of the horse chestnut, as long as they remain enclosed in the buds (Zeitsch. fur Chem., 1867, 84). It is described as an amorphous red-brown substance of the formula C₂₆H₂₄O₁₃, H₂O, having a strongly astringent taste.

Pinicortannic acid and cortepinitannic acid occur in the bark of the Scotch fir, Pinus sylvestris (Linn.), and can be separated owing to the fact that in aqueous solution the former only is precipitated by means of lead acetate. Pinicortannic acid forms a reddish-brown powder of the composition (C₁₆H₁₈O₁₁)₂, H₂O, which after drying is sparingly soluble in water. It gives a green coloration with ferric chloride, and when boiled with dilute acids gives the phlobaphene C₄₈H₅₀O₂₁ (Kawalier, Sitz. Ber., 11, 361).

Pinitannic acid and oxypinitannic acid occur in the needles of the Scotch fir, Pinus sylvestris (Kawalier), and are distinguished from one another by the fact that the former only is precipitated by lead acetate solution. Pinitannic acid, according to Rochleder (Sitz. Ber., 2 9> 6p), also present in the Thuja occidentalis, is a reddish-yellow substance which gives a red-brown coloration with ferric chloride and when boiled with dilute acids a sparingly soluble red product (phlobaphene).

Oxypinitannic acid, on the other hand, yields a green solution with ferric chloride (Kawalier).

Quebracho tannin or Quebrachitannic acid, see QUEBRACHO COLORADO.

Quinotannic acid or Cinchonatannic acid obtained from cinchona bark is a light yellow very hygroscopic substance, a solution of which gives a green precipitate with ferric salts. On digestion with boiling dilute sulphuric acid, it is converted into a sugar and cinchona red C₂₈H₂₂O₁₄ (Rembold, Annalen, 143, 270), and from the latter by fusion with alkali, protocatechuic and acetic acids are produced (Hlasiwetz, ibid., 143, 307). According to Schwarz (Sitz. Ber., 7, 250), quinotannic acid has the composition C₁₄H₁₆O₉, whereas cinchona red is to be represented as C₁₂H₁₄O₉.

>Quinovatannic acid, contained in the bark of the Cinchona nova, in many respects resembles quinotannic acid (Hlasiwetz, Annalen, 79, 129). With ferric chloride it gives a dark green coloration, and with boiling dilute acids quinova red C₁₂H₁₂O₅ is produced. On fusion with potash it yields protocatechuic acid.

Rhamnotannic acid (so-called), present in buckthorn berries, is in reality not a tannin matter.

Rhatany tannin, C₂₀H₂₀O₉, from the bark of rhatany root. Krameria triandra (Ruis and Pav.), (Willstein, Jahres., 1854, 656) is described by Raabe (ibid.) 1880, 1060) as a light yellow powder, readily soluble in water. Its solution gives with ferric chloride a green coloration. When heated with dilute acids it yields rhatany red, C₂₂H₂₂O₁₁, and a sugar (Grabowski, Annalen, 143, 274), whereas according to Raabe (loc. cit.) no sugar is thus produced and the red substance possesses the composition C₂₀H₁₈O₈. By dry distillation rhatany red yields catechol, and protocatechuic acid and phloroglucinol when fused with alkali.

Rheotannic acid or Rhubarb tannic acid, C₂₆H₂₆O₁₄, derived from rhubarb, forms a yellowish-brown readily soluble powder, the solution of which gives with ferric chloride a black-green precipitate. With boiling dilute acids it gives rheic acid (rheumic acid), C₂₀H₁₆O₉ and a fermentable sugar (Kubly, Zeitsch. fur Chem., 1868, 308), although according to Tschirch and Neuberger (Schweiz, Wochenschr. Chem. Pharm., 1902, 282) in this manner rheum-red, C₄₀H₃₂O₁₈, cinnamic acid, gallic acid, and sugar are produced. According to Gilson (Chem. Zentr., 1903, i., 722, 882), two glucosides are present, glucogallin, C₁₃H₁₆O₁₀, giving gallic acid and dextrose, and tetrarin, C₃₂H₃₂O₁₀, from which rheosurin, C₁₀H₁₂O₂, cinnamic acid, and gallic acid can be produced. According to Krembs (Inaugural Diss., 1903, Berne), a catechin is also present in rhubarb.

Rhodotannic acid, 4C₁₄H₁₂O₇, 3H₂O, found in the leaves of Rhododendron ferrugineum (Linn.), is an amber-coloured substance which gives a green coloration with ferric chloride solution. Heated with dilute mineral acids, a reddish -yellow precipitate of Rhodoxanthin, C₁₄H₁₄O₈, is produced (Schwarz, Sitz. Ber., 9, 298).

Rubinic acid, v. CATECHU.

Rubitannic acid, 2C₁₄H₂₂O₁₂ + H₂O, was obtained by Willigt (Annalen, 82, 340) from the leaves of Rubia tinctorium (Linn.). It gives a green colour reaction with ferric chloride.

Sequiatannic acid, C₂₁H₂₀O₁₀, was isolated from the cones of Sequoia gigantea (Torr), (California), by Heyl (Pharm. Zentr., 1901, 42, 379) as a reddish-brown powder, soluble in water and yielding the salts MgC₂₁H₁₈O₁₀ and CaC₂₁H₁₈O₁₀. Boiled with dilute sulphuric acid, a phlobaphene, gallic acid, and a sugar are produced. The hexa-acetyl, C₂₁H₁₄O₆(C2H₃O)₆, hexabenzoyl, C₂₁H₁₄O₁₀(C₇H₅O)₆, and bromine, C₂₁H₁₅O₁₀Br₅, derivatives of this tannin are amorphous.

Sorbitannic acid, from the juice of the ripe berries of the mountain ash, Sorbus ancuparia (Linn.), forms a thick syrupy mass, which gives a green coloration with ferric chloride solution. It yields catechol on dry distillation, and protocatechuic acid and phloroglucinol when fused with alkali (Vincent and Delachanal, Bull. Soc. chim., [ii.], 47, 492).

Spruce-bark tannin, C₂₁H₂₀O₁₀ (?) gives, according to Bottinger, an unstable bromo derivative C₂₁H₁₄Br₆O₁₀. This reacts with hydroxylamine hydrochloride, and with hydrochloric acid at 180-190° evolves methyl chloride. The penta-acetylpentabromo derivative C₂₁H₁₀Br₅O₁₀(C₂H₂O)₅ was also prepared. With boiling dilute hydrochloric acid the tannin yields spruce red which gives the acetyl derivative C₄₂H₂₇(C₂H₃O)₇O₁₇ and when suspended in chloroform and treated with bromine the compound C₄₂H₂₄Br₁₀O₁₇ (Bottinger, Ber., 17, 1127).

Strawberry-root contains a tannin fragarianin (Phipson, Jahres., 1878, 891), the solution of which gives a green colour with ferric chloride. Boiling dilute hydrochloric acid forms glucose and a red substance fragiarin. On dry distillation the tannin gives traces of catechol, and when fused with alkali protocatechuic acid is produced.

Tannecortepinic acid, C₂₈H₂₆O₁₂, according to Rochleder and Kawalier (Sitz. Ber., 29, 23), can be isolated from the bark of young Scotch firs collected in the spring time. Ferric chloride gives a green coloration and boiling dilute acid a phlobaphene in addition to a little sugar.

Tannopinic acid, C₂₈H₃₀O₁₃ (?) is sometimes present in the needles of the Scotch fir gathered in the spring (Rochleder and Kawalier). In the winter time, oxypinitannic acid (loc. cit.) appears to take its place.

Tea tannin is probably identical with the quercitannic acid of oak bark (Stenhouse, Phil. Mag., 23, 332; Rochleder, Annalen, 63, 205; and Hlasiwetz and Malin, J. pr. Chem., [i.], 101, 109).

Tormentilla tannin, C₂₆H₂₂O₁₁, from the root of Potentilla tormentilla (Neck.), is an amorphous reddish powder, which colours ferric chloride solution blue-green. Boiled with dilute acids it produces tormentil-red without appreciable formation of sugar, and this appears to have the same composition as the tannin itself. With fused alkali phloroglucinol and protocatechuic acid are obtained. The root also contains a substance which yields ellagic acid when boiled with potash solution (Rembold, Annalen, 145, 5).

Viridic acid, C₁₄H₂₀O₁₁ (?), which exists in coffee beans as a calcium salt (Rochleder, Annalen, 63, 197), is obtained by the air oxidation of an ammoniacal solution of caffetannic acid, and forms a brown amorphous mass, the alkaline solutions of which are green. The salts, Ba₂C₁₄H₁₆O₁₁, PbC₁₄H₁₂O₈, and PbCuH₁₄O₉, have been described (cf. also Vlaanderen and Mulder, Jahres., 1858, 261).

Willow bark tannin. The bark of Salix triandra (Linn.) contains a glucoside tannin which gives a green colour reaction with ferric chloride, and when boiled with dilute sulphuric acid a brownred precipitate (Stenhouse, Proc. Roy. Soc., u, 403; Johanson, Arch. Pharm., [iii.], 13, 103).

Tannins are frequently accompanied in the plant by yellow colouring matters, and it has been pointed out by Perkin that a relationship is usually to be observed between these compounds in respect of the phenolic nuclei present in each. Thus catechu contains catechutannic acid and quercetin, both of which contain phloroglucinol and catechol groups, whereas both the cyanomaclurin and morin of Jakwood (Artocarpus integrifolia, Linn.) yield phloroglucinol and β- resorcylic acid. Again, in sumach (R. coriaria, Linn.), Pistacia lentiscus, Linn, (leaves) and Hæmatoxylon campeachianum, Linn, (leaves), a gallotannin and myricetin exist, both of which are pyrogallol derivatives.

Other similar instances of this relationship could be cited; and where a divergence of this rule at first sight seems evident, this is frequently more apparent than real, as in the case of Young Fustic (R. cotinus, Linn.), which is known to contain a gallotannin and fisetin (catechol and phloroglucinol). From the reactions of the wood extract, however, catechol tannin must also be present.