DYEING AND CALICO PRINTING. 307 



colour is itself perfectly colourless, until it is combined with an acid 

 and becomes red ; thus when the colourless substance, named rosani- 

 line, or 



C 20 H 10 N s H 2 O 



combines with acetic acid, acetate of rosaniline or magenta is formed, 

 and constitutes the beautiful crowns of roseine exhibited by Messrs 

 Simpson and Co. It is easy to prove by Dr. Hofmann's extremely in- 

 genious process, that roseine is an acetate of rosaniline, for by boiling 

 roseine with ammonia, colourless crystals of ammonia are liberated. 

 There is no doubt that the aniline purples and blues will be also traced 

 to a colourless alkaloid, and it would not be surprising if this should 

 prove to be isomeric or homologous with that producing roseine. 



Messrs. Laurent and Casthelaz, of France, have exhibited a red 

 colour from coal-tar which deserves attention, as it is produced by a 

 new and highly interesting chemical reaction, directly from nitro-ben- 

 zine without the intermediate process of converting the latter into 

 aniline. This product will be found under the name of erythro-ienzhte 

 in their case. 



Messrs. Simpson, Maule, and Nicholson have also exhibited a beau- 

 tiful yellow from aniline, which they call phospheine, and a superb 

 purple called regina purple, which is obtained by carefully heating 

 roseine in a suitable apparatus at a temperature of about 400°. The 

 mass obtained is heated with acetic acid and alcohol, when the regina 

 purple is dissolved. 



Put to describe only the colours obtained from aniline would give 

 an inadequate idea of the fertility which enables coal-tar to yield to the 

 researches of the chemist such a variety of splendid dyes. Thus, for 

 example, in 1860, Messrs. Guinon, Manias, and Bonnet, of Lyons, in- 

 troduced a beautiful brilliant blue colour from coal-tar products, under 

 the name of azuline, obtained from phenyc acid. These gentlemen, as 

 well as Messrs. W. Adshead and Co., also exhibit specimens of silk 

 dyed with another coal-tar product called picric acid, which is obtained 

 by the action of nitric acid on carbolic acid. This beautifid yellow dye 

 well known in 1851, has been extensively used with the coal-tar blues 

 for the production of excellent greens, which possess the property of 

 remaining green by artificial light. But the best examples of dyed- 

 green silk-skeins in the Exhibition are those dyed with picric acid and 

 then with very pure sulphate of indigo The dyer, however, replaces 

 the sulphate of indigo by Prussian blue, when his object is to produce 

 a green which shall appear as such by artificial light. 



These observations should not be brought to a conclusion without 

 remarking that the coal-tar colours deserve, attention for their power as 

 well as for the facility with which they may be applied, for one grain 

 will deeply tint half a gallon of water, and little or no skill is required 



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