720 CAEBON 



yielding a rod powder. The colouring principle has been isolated in a puro form, and 

 carefully studied by Messrs. Dale and Schorlemmer. 1 Aurin is used for giving a very 

 tine orange-yellow colour to silks and albuminized cotton. 



RED DYES : Pceonin, or Bed Coralline. By heating aurin with aqueous ammonia 

 to about 140 or 150 C. (284 or 302 F.), a now colouring agent is obtained, which 

 dyes wool and silk with a redder colour than can bo obtained from aurin. This 

 beautiful scarlet dye, known as paeonin, was discovered in 1860 by M. Persoz, jun., 

 and its manufacture has been perfected by Messrs. Grunon, Mamas, and Bonnet, of 

 Lyons. 



It is believed that coralline is very closely related to, if not identical with, the 

 rosolic acid originally obtained from coal-tar by Eunge, and readily prepared by the 

 oxidation of phenol. 



BEOWK DYES : Picramic acid. This was obtained by WShler by acting on picric 

 acid with proto-sulphate of iron, neutralising the product with caustic baryta, and 

 finally removing the baryta by sulphuric acid. Picramic acid is a deep brown 

 substance, used for dyeing silk. 



Phenicienne or Phenyl brown. Eoth discovered this substance in 1863, by acting on 

 carbolic acid with nitre-sulphuric acid. The product is an amorphous brown powder, 

 said to be a mixture of two distinct substances the one yellow, and the other 

 blackish-brown. A variety of shades, from a deep red to a golden buff, may be given 

 to wool and silk by means of picramic acid. 



Soluble Garnet (Grenat soliible). This is the isopurpurate of potash, obtained by 

 acting with cyanide of potassium on a solution of picric acid. It has been introduced 

 as a dye-stuff by M. J. Casthelaz. As it is explosive when dry, it should be kept as a 

 paste and moistened with glycerine. 



BLTTE DYB : Azidine, Azurine, Phenol-blue or phenyl-blue. By heating coralline, 

 or rosolic acid, with aniline, and treating the product with sulphuric acid, a blue 

 colouring-matter is obtained in the form of a reddish substance exhibiting golden 

 tints. This is the dye known as Azuline. 



GBEEX DYE : Viridine. A green dye has been obtained by Messrs. Grunon, Marnas, 

 and Bonnet, by acting on rosolic acid with aniline and benzoic acid. 



CARBON. (Symbol, C; Atomic weight, 6). Carbon exists in a considerable 

 variety of forms, most of which are so unlike each other, that it is not surprising the 

 older chemists should have believed them to be compounds. 



Diamond. The purest variety of carbon is the diamond. This gem crystallises in 

 the regular octahedron and derived forms. The diamond does not owe its hardness 

 and brilliancy solely to its purity, for many specimens of graphite consist of carbon as 

 free from admixture as the best diamonds. The density of graphite and of diamond, 

 however, is very different ; for while the former seldom exceeds 2'45, and is often 

 much lower, the diamond is very constant, generally ranging between 3*51 and 3 - 55. 

 Diamonds, if they are perfectly transparent, leave no residue when burnt in oxygen 

 gas. If not clear, they yield from 0'05 to 0'20 of ash, consisting chiefly of peroxide 

 of iron, but also containing traces of silica. The refractive power of diamonds is 

 as high as 2'439. Sir Isaac Newton, observing that oily or inflammable bodies gene- 

 rally possessed the greatest refractive powers, inferred from the high index of refrac- 

 tion of the diamond, that it was ' an unctuous body congealed.' This idea will 

 appear the more happy, when it is considered that the ashes of the diamond exhibit a 

 structure resembling that of vegetable parenchyma. 



In freedom from ashes, certain graphites nearly approach the diamond, some 

 natural varieties not yielding more than 0'33 per cent. See DIAMONB. 



Graphite. This kind of carbon is found in many parts of the world, and in dif- 

 ferent degrees of purity : it is also formed artificially. Some native varieties are 

 exceedingly soft, of a black or greyish tint, metallic lustre, and, in consequence of 

 making a streak on paper, of various degrees of blackness, according to tho mode of 

 preparation and other circumstances, are invaluable for the manufacture of artists' 

 pencils, and are hence called ' Black Lead. 1 



A very hard graphite is found lining the retorts in which coal-gas is made : it is, 

 when cut into plates or rods, used in galvanic arrangements, either for tho poles or 

 for the inactive elements of batteries. See GHAPHITE and PLUMBAGO. 



A very dense form of carbon, having high electric conductivity, and sometimes used 

 for the negative element in Bunsen's battery, may be obtained by heating to redness 

 an intimate mixture of finely-divided coke and coal in the proportions of two parts of 

 the former to one of the latter ; this mixture having been ignited in an iron mould, 

 is dipped several times in treacle, and again strongly heated. A hard compact substance 

 is thus obtained, capable of being sawn to any required shape. 



1 ' Journal of the Chemical Society,' [2] xl. 1873, p. 434. 



