THE ANILINE DYES* 
435 
appear to clear up a mystery that has hung over the produc- 
tion of aniline dyes in general. It will be seen from what 
precedes, that the colours in question are produced whenever 
aniline is submitted to the action of oxydising agents (chloride 
of lime, nitric acid, bichloride of tin, bichromate of potash, 
ozone, &c.), and according to the particular oxydiser we make 
use of, we obtain one shade or another : hence a considerable 
number of patents ; hence also several severe law cases, &c. 
It passed, then, as a fact, that when aniline was oxydised it 
gave magenta. One morning, however, not many months 
ago, Dr. Hofmann took some pure aniline and found that it 
gave no magenta whatever ! It is known that commercial 
aniline always contains toluidine — another base Very similar 
to aniline, and produced exactly in the same manner. In coal 
naphtha along with benzol C 12 IF we find toluol C 14 H 8 , so 
along with nitrobenzol C 12 H 5 , N O 4 , we obtain nitrotoluol 
C 14 H 7 , N 0 4 , and along with aniline C 12 H 7 N we get tolui- 
dine C 14 H 9 1ST. In fact, the benzol, nitrobenzol, and aniline 
of commerce are mixtures of the bodies just named, in various 
proportions, and whose boiling points differ almost in every 
sample ; for whereas benzol boils at 80°, toluol only boils at 
108 ° ; aniline (pure) at 182°, toluidine (pure) at 198°. 
It was natural, then, that Dr. Hofmann should take pure 
toluidine in making his next experiment ; but still he obtained 
no rosaniline ! As a last resource, he mixed the two sub- 
stances aniline and toluidine together, when, upon submitting 
the mixture to the action of an oxydiser, he immediately 
obtained the dye. What appears to happen is this : 2 equiva- 
lents of toluidine and 1 equivalent of aniline are acted upon 
together by the oxydiser, lose by its action 7 equivalents of 
hydrogen, and give rosaniline — 
2 C 14 H 9 N + C 12 H 7 N = C 40 H 25 N 3 
Toluidine. Aniline. 
and — 
C 40 H 25 N 3 — 7 H = C 40 H 19 N 3 
minus Hydrogen. Rosaniline. 
So we see that it is not the purest samples of commercial 
aniline which furnish the aniline dyes. Pure aniline, as already 
noticed, boils at 182°; but the manufacturers of dyes prefer 
anilines which boil from 185° to 210°. It is more than pro- 
bable that in commercial aniline we have several other sub- 
stances present besides toluidine, and whether these affect the 
colours in any way remains to be determined. 
We have seen how mauve or aniline purple is produced, let 
us now turn to the production magenta, rosaniline, or aniline 
crimson. If we heat a little aniline in a test tube with 
