436 
POPULAR SCIENCE REVIEW. 
bichloride of tin, bichloride of mercury, for instance, we get 
immediately the splendid aniline crimson known by so many 
fancy names. Its colouring power is as intense as that of 
mauve noticed above. Mr. Nicholson has obtained this colour 
in its pure state, and it has been submitted to analysis by Dr. 
Hofmann and others. Like mauveine, it is a powerful base, 
having for formula C 40 H 19 N 3 , generally containing, more- 
over, 2 equivalents of water, and then slightly coloured ; but 
in its absolutely pure state } it is colourless . It is called rosani- 
line in chemistry, and on uniting with acids forms well-charac- 
terised salts, crystallising perfectly, and possessed of the vivid 
crimson colour which constitutes the dye.* Thus the magenta 
dye is always a salt of rosaniline, pure rosaniline itself being 
devoid of colour, or nearly so. The hydrochlorate of rosani- 
line is C 40 H 19 N 3 , H Cl ; the acetate of rosaniline was 
exhibited in the shape of a crown of beautiful crystals in 
the Exhibition of 1862, by Mr. Nicholson : this mass of 
crystals valued about £100 sterling. 
If we inquire how it happens that so expensive a substance 
can have become so soon the object of an important manufac- 
ture, we find it is simply because a very small quantity of 
rosaniline goes a very long way as a dye. Moreover, nothing 
is simpler than the operation of dying with this substance. 
Silk or wool thoroughly cleaned has only to be plunged into a 
solution of mauve or magenta, taken out and washed. The 
dye is fixed in an instant, no previous preparation nor mor- 
dants are required. Not so, however, with linen, cotton, 
paper, or vegetable substances ; upon these the dye has no hold 
unless they have been previously coated with gluten or some 
other nitrogenous or animal substance : it is upon animal 
fibres, such as silk and wool, that the aniline dyes adhere so 
easily ; hence they readily stain the fingers of the operator. 
Hosaniline is produced when commercial aniline is acted 
upon by bichloride of tin, bichloride of mercury, arsenic acid, 
nitric acid, per chloride of iron, &c. Most of these different 
processes for obtaining modifications of the same substance 
have been made the objects of numerous patents. MM. Lau- 
rent & Casthelez have recently succeeded in converting 
nitrobenzol directly into aniline red by heating it with a 
mixture of iron and hydrochloric acid, or with protochloride of 
iron. In this process aniline is produced during the operation, 
and also perchloride of iron. When the mixture is heated, 
this perchloride reacts on the aniline to form the crimson dye. 
It will be remembered that Preisser, in an ingenious paper published 
some years ago, showed that most colouring matters are, in the pure state, as 
colourless as white sugar. 
