On a new Gold Varnish which does not lose its Colour by exposure to Air and Light.

The Chemical Gazette 318, 15.1.1856

A very beautiful and permanent gold varnish may be prepared in the following manner: - 2 ozs. of the best French garancine are digested in a glass vessel with 6 ozs. of alcohol of spec. grav, 0.833, for twelve hours, pressed, and filtered. A solution of clear orange-coloured shell-lac in similar alcohol is also prepared, filtered, and evaporated until the lac has the consistence of a clear syrup; it is then coloured with the tincture of garancine. Objects coated with this have a colour which only differs from that of gold by a slight brownish tinge. The colour may be more closely assimilated to that of gold by the addition of a little tincture of saffron.

— Archiv der Pharm., cxxxiv. p. 78.


On Rinmann's Green.

The Chemical Gazette 336, 15.10.1856

By Prof. R. Wagner.

Under the name of Rinmann's green (cobalt-green) is known a colour obtained in the latter part of the last century by Rinmann, a Swede, by the calcination of a mixture of oxide of zinc and prot oxide of cobalt. The high price of the materials may be the principal reason why this colour has not come into general use. But since zinc-white has become a regular and cheap article of commerce, and protoxide of cobalt has also been brought into commerce at a low price and in a tolerably pure state, the conditions for the manufacture of cobalt-green have become more favourable than formerly, and the author has made experiments upon its preparation, of which the following are the results.

In the first place it is necessary to prepare a protoxide of cobalt as free as possible from foreign metals. For this purpose oxide of cobalt, such as is furnished by the Saxon blue manufactories, is employed; this is dissolved in 3 parts of concentrated muriatic acid, the solution is evaporated in dryness, the residue dissolved in 6 parts of water, and sulphuretted hydrogen gas is passed through the fluid as long as a precipitate is formed. The fluid fileted from the precipitated metallic sulphurets is again evaporated to dryness, and the residue is dissolved in so much water that the solution shall weigh 10 parts. A litre of the solution does not contain much less than 100 grms. of protoxide of cobalt, and 100 cub. centims, therefore contain 10 grms. The fluid is drawn off for use.

If this solution be precipitated with carbonate of soda, and the hydrated protocarbnate of cobalt produced be mixed whilst still moist after washing with oxide of zinc, a reddish-violet paste is obtained, which, when dried and long calcined, forms a green mass, the colour of which is intense in proportion to the quantity of solution of cobalt employed. Cobalt-green may be regarded as a mixture of zincate of protoxide of cobalt (corresponding to the aluminate of protoxide of cobalt in cobalt-ultramarine, or Thenard's blue) with oxide of zinc. From well-calcined cobalt-green ammonia first of all extracts oxide of zinc, and afterwards the cobalt compound dissolves. Glass fluxes, as might be expected, are coloured blue by cobalt-green. If the cobalt solution be employed in such quantity that there may be more than 1 equiv. of protoxide of cobalt to l equiv. of oxide of zinc, a dingy green or even black mass is obtained after calcination; this is probably a mixture of the compound ZnO, CoO with an excess of protoxide of cobalt. The most agree able greens are obtained when 1 to 1½ part of protoxide of cobalt is employed with 9 to 10 parts of oxide of zinc. The tints however never equal those of a bright copper-green, nor even those of the green ultramarine.

The Belgian chemist Louyet has ascertained that an addition of phosphoric or arsenic acid in the preparation of cobalt-ultramarine increases the beauty of the colour. If the addition of acids favours the combination of protoxide of cobalt with alumina, the presence of these acids must also have a favourable influence on the production of cobalt-green. If the above-mentioned solution of cobalt be precipitated by phosphate of soda or arseniate of potash, the phosphate or arseniate of protoxide of cobalt thus obtained possesses the property of communicating the green colour to oxide of zinc, even at a lower temperature than ordinary protoxide of cobalt. The protoxide of cobalt is also broken up and rendered more productive by these two acids, and the green colour is rendered purer and more brilliant. Alkaline arsenites behave like the arsenites and phosphates. If the mixed mass is obtained, to which the arsenious acid, which is partially volatilized, has given a loose spongy consistence, in consequence of which it is easily triturated.

Experiments with silicic and boracc acids and oxide of antimony did not give favourable results.

- Kunst- und Gewerbeblatt für Bayern, 1856, p. 83.


Note on the Oils employed in the Manufacture of Turkey-red.

The Chemical Gazette 332, 15.8.1856

By J. Pelouze.

All the fixed oils are not equally proper for the preparation of the dyes known under the names of Turkey-red and Adrianople-red. Those generally used are olive oils, distinguished by the name of emulsive oils (huiles tournantes), from the property which they possess of producing a milky emulsion with a weak alkaline solution. To distinguish them, the manufacturers let fall 1 or 2 drops of the oil into a test-glass partly filled with a solution of caustic soda marking 1½ to 2 degrees, and judge of the value of the oil by the greater or less opacity of the drops of oil. The oils proper for the manufacture of Turkey-red being expensive, it has been endeavoured to replace them by cheaper oils, mixed with yolk of egg, treated with nitric acid, &c., but without success, as the manufacture of Turkey-red still consumes great quantities of natural emulsive oils.

* Chem. Gas, No. 301, p. 161.The author formerly showed* that if crushed oleaginous seeds were left to themselves, the neutral fatty bodies contained in them were chaged into acids, and announced that these partially acidified oils would then shortly be applied in the manufacture of Turkey-red. He has ascertained that the oils used for that purpose were mixtures of neutral and acid fatty bodies; and by treating them with alcohol, found that they yielded portions of oleic and margaric acids varying from 5 to 15 per cent. The acids may also be extracted from the oils by heating them for a few minutes with an alkali. Ordinary olive oil contains no fatty acids, or only an insignificant quantity of them.

The author's observations on the spontaneous saponification of fatty bodies easily explain the difference in the composition of these oils. The pure oils are obtained by the simple division and immediate pressule of the olives, whilst the treatment of the cakes and other residues, and the fermentation of the olives, cause the acidification of the oil, and render it emulsive (tournante).

For some years M.M. Boniface of Rouen have prepared an artificial oil of this kind; and the author, on examining it, found it to contain considerable portions of oleic and margaric acids, but the process by which it is prepared is not known. However, it appears that the only difference between the two categories of commercial oils—those fitted for dyeing are mixed with fatty acids, whilst the others are free from them. M. Chevreul, also, more than twenty years ago, extracted two oily matters from Turkey-red stuffs; one of these was neutral to litmus, whilst the other reddened it, and was composed of oleic and margaric acids.

The author states that olive-oil has been almost exclusively employed in dyeing Turkey-red, because olives give rise to the reaction which produces the fatty acids more readily than the oleaginous seeds, and that it will be easy to substitute for it cheaper oils, such as poppy-oil, oil of sesame, colza-oil, palm-oil, &c. It will be sufficient to crush the seeds or kernels, and leave them for a short time before extracting the oil. A still more simple means consists in adding to the oils a few hundredths of their weight of the oleic and margaric acids furnished by the manufacturers of stearine candles. This last method has succeeded with M. Steiner of Manchester, and M. Pelouze also communicates a letter from MM. Henry of Barle-Duc, containing some useful information on the substitution of artificially acidified oils for those which are naturally acid, and exhibited to the Academy of Sciences specimens of cotton-dyed Turkey-red with both the natural and artificial oils, and between which there was no perceptible difference.

He adds, that it is very probable that the treatment of certain oils, especially colza-oil, with a little sulphuric acid, would give rise to mixtures of neutral oils and fatty acids, which when well washed would be fit for the manufacture of Turkey-red.

MM. Henry state that the quantity of oleic acid required to give the necessary properties to the oil varies according to the nature of the latter from 5 to 15 per cent, and they have even produced the effect with 2 per cent. The oils require to be purified to a certain extent. The cotton-dyed (10 kilogrms. of thread) gave a good tint, proportioned to the madder employed; the oil used was 3 kilogrms. of purified colza-oil with 60 grms. of oleic acid, or only 2 per cent. They are convinced that it will succeed on the large scale.

— Comptes Rendus, June 23, 1856, p. 1196.