62 
POPULAR SCIENCE REVIEW. 
of the transformations may be given without taking up much 
space. Benzol consists of the elements carbon and hydrogen 
in the proportion of twelve of the former to six of the latter. 
The action of the nitric acid upon this is to remove one of the 
hydrogen atoms and put in its place an atom of peroxide of 
nitrogen. When this nitro-benzol is acted upon by certain che- 
mical agents of the class called reducing (as for instance a 
mixture of iron-filings and acetic acid which is now generally 
used), the whole of the oxygen which the peroxide of nitrogen 
lias brought into the nitro-benzol is removed, and two parts of 
hydrogen are added, so that the original benzol becomes trans- 
formed into a body containing twelve parts of carbon, seven 
parts of hydrogen, and one part of nitrogen. This is aniline, a 
substance which illustrates in a striking manner the effect that 
demand exerts upon supply. Some years ago all the labora- 
tories in Europe did not contain a pound weight of it, whereas 
it is now manufactured by thousands of gallons at a time. 
There is still another stage to be passed before we get to the 
colouring matter, but here the change is by no means well 
understood, and the best processes are kept scrupulously secret. 
The action is, however, the reverse of the one just now de- 
scribed, being the addition instead of subtraction of oxygen, 
and it is by the employment of different oxidising agents that 
we get mauve, magenta, roseine, azuline, bleu de Paris, and 
other gorgeous dyes which have received arbitrary names. 
Mauve or aniline purple was first discovered by Mr. Perkin, 
and in his case at the Exhibition may be seen a very complete 
and beautiful collection showing the different stages of the 
manufacture, from the crude coal oil up to a gigantic block of 
the pure dye itself upwards of a cubic foot in bulk, and for the 
production of which the distilled products from 2,000 tons of 
coal were consumed. The tinctorial properties of this dye are 
very strong. Mr. Perkin illustrates this by exhibiting a gallon 
jar filled with a beautiful violet solution, the colour of which is 
communicated to the water by one grain only of the dye. To 
render this illustration more striking there is placed near it a 
similar sized jar filled with crude coal-tar, the whole of which 
would have to be employed to produce this single grain of 
colouring matter. 
The gigantic scale upon which the manufacture of these 
colouring matters is carried on and the perfection to which it is 
brought are strikingly illustrated by Messrs. Simpson, Maule, 
and Nicholson. This firm have succeeded in producing the 
beautiful colour known as magenta in a crystalline form, and 
one of the most striking objects in the whole department is the 
magnificent crown of acetate of rosaniline (the chemical name 
for magenta), which occupies so prominent a position in their 
