CHEMISTRY. 201 



the temperature of the crystal while under examination. — Me- 

 chanics'' Magazine. 



ANILINE COLORS. 



The starting-point of the manufacture of these colors is the ben- 

 zole of coal-tar, mixed, as is usually the case, with a variable pro- 

 portion of toluol. The boiling-point of this mixture is about 90^^ 

 C, and it yields nitro-benzole, which boils at 235° C, while pure 

 nitro-benzole has it at 213° C. 



The conversion of pure nitro-benzole into aniline is brought 

 about by Bechamps' process, — metallic iron and acetic acid, — 

 which is performed in iron tanks provided with stirrers and heated 

 by steam ; the top being closed by a species of still-head enables 

 the volatilized products to be collected. 



Commercial aniline is never chemically pure, but presents a 

 mixture of pure aniline, toluidine, and odorine. Ordinarily it is 

 free from quinoline, which is obtained directly from the basic oils 

 of the heavy tar-oils. Its color is from ^-ellow to dark-brown, and 

 has the odor peculiar to odorine, a liydrocarbon boiling at 133'' C. 

 Its boiling-point is rarely found to agree in any two samples, as 

 it varies from 180° C. to 250° C, at which latter degree it remains 

 constant. If the boilin.o: commences below 180° C. it indicates the 

 presence of considerable quantities of odorine, which makes it of 

 poor quality. 



The aniline used for the various colors is taken of different com- 

 position and boiling-point. A. W. Hofmann has shown that a 

 mixture of an equivalent of aniline and two of toluidine produces 

 the largest yield of rosaniline (fuchsine). The substance used for 

 this manufacture begins to boil at about 175° C. ; till 190° C. some 

 10-15 per cent, have passed over, and up to 200° C, when 80 per 

 cent, pass over, it rises very gradually. 



Aniline blue and purple require an oil which begins to boil at 

 190° C, and at 200° C. has lost only 60 per cent. Evidently with 

 these properties it contains less aniline than the preceding one. 



The changes which these bases undergo when converted into 

 dyes, or compounds of rosaniline, are brought about by the de- 

 struction of a portion of them. 



Neither pure aniline nor toluidine alone produce the colored 

 alkaloid, but with substances like chloroform, chloride of carbon, 

 iodide of cyanogen, iodoform, or formiates, as well as with iodine 

 and corrosive sublimate, the change occurs. 



Aniline blue results from various processes. The one most 

 commonly used at present is that of Girard and De Laire, the Bleu 

 de Paris, made by heating fuchsine with fluid aniline. The origi- 

 nal process produced a blue with a reddish tinge ; but by the addi- 

 tion of some organic substances, acetic acid, methylic alcohol, the 

 blue is obtained pure. It is distinguished from all other blues by 

 not appearing green in candle-light. 



The various shades of purple to blue and violet are made from 

 fuchsine by Hofmanu's method, that is, heating (1) fuchsine and 



