COLOUR-TESTS FOR STRYCHNIA, ETC. 
429 
which give rise to a similar reaction. The answer must be, 
in a qualified sense, in the affirmative; but it must be under¬ 
stood that the reaction is only similar, not the same . 
Such a substance is to be found in cod-liver oil, which, 
when treated with strong sulphuric acid, assumes a purple 
tint, mixed with streaks of blue, changing after a time to 
mulberry, and from that to a red-brown. In these changes 
of colour there is such a general resemblance to the strychnia 
tints as would justify their being put forward as an objection 
to the colour-tests, but for the very obvious consideration 
that with sulphuric acid alone strychnia undergoes no change 
of colour. The very fact, too, that cod-liver oil is an oil, 
while strychnia is tested either as an alkaloid or the salt of 
an alkaloid, as a crystal or as a white powder, or as a dry 
deposit from a liquid holding it in solution, deprives this 
objection to the colour-tests for strychnia of all practical 
value. 
Again, aniline is mentioned as a source of fallacy. But 
aniline is a coloured liquid, which yields with sulphuric acid 
a dense white precipitate, the sulphate of aniline. Strychnia, 
on the other hand, is a crystal or white powder, or a dry 
deposit from a liquid holding it in solution. 
But the sulphate of aniline which is formed bv adding the 
strong sulphuric acid to the liquid aniline, is sold as a white 
powder, as are some specimens of strychnia. Hence the 
sulphate of aniline might possibly prove a source of fallacy, 
inasmuch as it gives no change of colour with sulphuric acid, 
and yet when treated with the colour-producing substances, 
yields a colour similar to the blue of strychnia . But the sul¬ 
phate of aniline, in place of a rich deep blue passing speedily 
into mulberry and at length into bright red, assumes at first 
a pale green, which deepens by slow degrees, then passes 
into a beautiful blue, continuing unchanged for a long- 
period, but at length turning to a black. So that the first 
characteristic colour with strvchnia is the second with ani- 
line, and the transient colour with strychnia is persistent 
with aniline. 
Again, there is a red crystalline substance, pyroxanthine, 
which produces with sulphuric acid alone, without addition 
of the colour-producing tests, a blue similar to that produced 
by strychnia. But there is here no real fallacy, because 
strychnia is not coloured, and does not yield any colour with 
sulphuric acid alone. 
Nor do papaverine and narceine, which are tinged purple 
by sulphuric acid alone, create any difficulty, or occasion any 
fallacy. And the same may be said of the whole body of 
