The elements of materia medica and therapeutics: 1. Plumbago vel Graphites. — Graphite or Black Lead.

The elements of materia medica and therapeutics
by Jonathan Pereira, M.D. F.R.S. & L.S.
Fourth Edition, enlarged and improved, including notices of themost of the medicinal substances in use in the civilized world, and forming an Encyclopædia of Materia Medica.
Vol. I.
London: printed for Longman, Brown, Green, and Longmans, Paternoster Row.
1854.

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¹ Essays, p. 246.

² Historia Naturalis, lib. xxxiv. cap. 47, 50, and 53, ed. Valp.

³ London Medical Gazette, vol. xviii. p. 267.

⁴ [In reference to the sources of plumbago, we find the following among some notes left by the late Dr. Pereira: — "Visited the Borrowdale lead mine; was told no plumbago bad been sent to market for three years; now engaged in running a level in order to find the vein; not been successful at present; the old workings are discontinued" (July 1849). In a note to Dr. Pereira, from a correspondent, we also find it stated that "Mexican black lead is much adulterated; sand, black clay, powdered black lead crucibles, and inferior qualities of lead, being used for the purpose. The finest plumbago is called pencil lead: the inferior, Naples lustre, Mexican jet, &c. Spanish plumbago is scarcely in the market."]History. — Plumbago (so called from its resemblance to plumbum or lead,) or graphite (from [], I write, on account of its use as a writing material), was probably known to the ancients; but it was first accurately distinguished from other bodies with which it had been previously confounded, especially with molybdena (bisulphide of molybdenum), by Scheele,¹ in 1779.

The terms plumbago, plumbum nigrum, and molybdena, met with in Pliny,² do not apply to graphite.

Natural History. — It is found in various parts of the world; chiefly in primitive rocks and the coal formations. It occurs at Borrowdale in Cumberland, in various parts of the continent of Europe (Bavaria, Bohemia, Spain, &c.), in Ceylon, and in the United States of America. A very pure graphite is found near Bustletown in Pennsylvania.

Graphite is found either crystallized or compact. Crystallized graphite (graphites crystallinus) may be foliated, scaly, or radiated,: its forms are thin six-sided tables belonging to the rhombohedric system. Compact graphite (graphites solidus) occurs either massive or disseminated.

Borrowdale plumbago is of fine quality. It is brought to London, and sold by auction at a public-house in Essex- street, Strand, on the first Monday in every month.³ The best quality usually sells for two guineas or more per pound, and is employed for making pencils.

Spanish Plumbago is imported from Malaga, It is probably obtained from the mountain of Mora, near Marbella, in Andalusia. It is sometimes of superior quality.

Ceylon or East India plumbago is another sort which is extensively imported. Its quality is inferior.

German plumbago is imported from Hamburgh. It is of inferior quality, and is said to be the produce of Bohemia. The so-called Mexican black lead is imported from Hamburgh.⁴

Properties. — As found in commerce, it is usually in kidney-shaped masses. Its colour is iron or steel-grey, with a metallic lustre. It has a greasy feel, and writes easily on paper. Its specific gravity is 2.08 to 2.45.

Characteristics. — It is known to be carbon by its yielding carbonic acid by combustion in oxygen gas. When burned, it usually leaves a residuum of silica and red oxide of iron. It is infusible before the blow-pipe. Its physical properties distinguish it from most other varieties of carbon. Some kinds of coal-gas charcoal (artificial graphite) closely resemble it. Of noncarbonaceous substances, molybdena (bisulphide of molybdenum) is the only substance that can be confounded with it in external appearance.

Purity. — Graphite usually contains traces of iron and silica. When of good quality it is free from all visible impurities (sand, stones, &c.) When heated before the blow-pipe, it should be infusible, and not evolve any odorous vapour or smoke: its freedom from metallic sulphurets (as of antimony and lead) is thereby shown. It is insoluble in alkalies and acids. Hydrochloric acid boiled with it should dissolve only some minute portions of iron; and the filtered acid liquid should yield no precipitate on the addition of carbonate of ammonia; and no change of colour when sulphuretted hydrogen is added to it.

The powder sold in the shops under the name of black lead, for polishing iron grates, &c. is an adulterated article, and is unlit for medicinal purposes. It is usually prepared by reducing the quality of the so-called Mexican plumbago (German plumbago) by grinding it with sand, old black lead crucibles, a substance called Bideford black (which am informed is a kind of black clay found near Bideford in Devonshire), and an inferior plumbago called common lead, seconds, or German gunpowder (from its being granulated like gunpowder). When reduced, it forms Naples lustre, Mexican jet, black lead, &c.

¹ Pharmaceutisches Central-Blatt für 1838, p. 524.

² Ann. Chim. el Physiq. 3ème ser. i. p. 1-54.

³ Silliman's Journal, vol. x. p. 105.

⁴ Proceedings of the Chemical Society, No. i. p. 12, 1841.

⁵ Ausfürlihe Arzneimittellehre, Bd. iii. p. 486, Berlin, 1828.Wackenroder¹ has signalised the existence of a commercial graphite, of which three-fourths were sulphuret of antimony.

For ordinary purposes, powdered graphite is purified by boiling it with nitro-muriatic acid, and then washing and drying it.

Dumas and Stas² purified it for analysis by heating it to redness with caustic potash, then washing it with water, boiling with nitric acid and nitro-muriatic acid to extract iron and bases, washing, drying, and then exposing it, at a white heat, to a stream of dry chlorine gas, by which chloride of iron and chloride of silicon were volatilised. When thus purified, it contained merely a trace of silica.

Composition. — It consists essentially of carbon, but is usually mixed with variable proportions of silica, iron, and other substances. The following are analyses of three varieties by Vanuxen:³
... | Borrowdale (pure) | Borrowdale (impure) | Bustletown (pure)
Carbon | 88,37 | 61,27 | 95,4
Water | 1,23 | 5,33 | 0,6
Silica | 5,10 | 10,10 | 2,6
Alumina | 1,00 | 3,20 | 0,0
Oxides of Iron, Mangmese, &c. | 3,60 | 20,00 | 1,4
Plumbago | 99,30 | 99,90 | 100,0

I suspect, however, that the finest varieties of the Borrowdale graphite contain a smaller quantity of foreign matter than is here stated. Graphite has been recently analysed by Dr. It. F. Marchand,⁴ who states that 1,4580 gramme of native graphite left a residue of pure white silica, without a trace of oxide of iron, weighing only 0.0075.

On the erroneous supposition that the carbon was chemically combined with iron, graphite was formerly called carburet or percarburet of iron. From some observations of Schrader, however, it would appear that the iron is in combination with titanic acid.

Physiological Effects. — Various properties have been assigned to it; but further evidence is wanting to establish its action on the body. Richter⁵ says it alters, in some way, the lymphatic secretion and the condition of the skin; and, after some days' use, causes increased secretion of urine, with difficulty in passing it.

Uses. — It has been employed both externally and internally in chronic diseases of the skin (as herpes). When used externally, it is employed in the form of ointment (Vnguentum plumbaginis), composed of from one to six drachms of plumbago to an ounce of lard. Internally the dose is ten or twelve grains to a drachm, or more.