COLOUR-TESTS EOR STRYCHNIA, ETC. 
791 
The sulphuric acid produces in strychnia no change of 
colour. Hence the acid itself becomes a test of no mean 
value. It serves, as I shall point out more particularly 
presently, to distinguish strychnia from a considerable 
number of the alkaloids, and also from several substances 
which give with sulphuric acid alone coloured reactions, 
some of which reactions with the acid alone bear a certain 
resemblance to those of strychnia with sulphuric acid plus 
the bichromate of potash, ferricyanide of potassium, per¬ 
manganate of potash, peroxide of lead, or peroxide of 
manganese. In order to distinguish strychnia from other 
alkaloids, and from the substances to which I have just 
referred, it is essential that the sulphuric acid should be first 
applied to, and well mixed with, the strychnia, and that the 
absence of colour having been noted, the reagents that 
develop the colour should be in their turn applied. In all 
that I have said on the subject of the colour-tests for 
strychnia, and in what I have yet to say, I assume this 
mode of procedure to be strictly observed; and I shall con¬ 
tinue to speak of these reagents as the colour-producing tests. 
I have hitherto assumed that the sulphuric acid is applied 
colcl; but I shall presently point out that we may greatly 
add to the value of this constituent portion of the colour- 
tests by first warming and then heating the acid solution. 
A very slight rise of temperature serves to develop very 
beautiful and characteristic colours in some of the alkaloids, 
while it does not change the colour of strychnia. A further 
rise of temperature, to the point of causing the mixture to 
give off vapour, develops colour in strychnia also, and deep¬ 
ens or changes the tints already imparted to the alkaloids 
previously affected by warming the acid mixture. 
The colour imparted to a solution of strychnia in sulphuric 
acid, by raising it to a temperature at which it gives off 
vapour, is not strongly marked. It is a faint yellow or light 
greenish-brown, differing somewhat in depth of tint wdth 
different specimens of strychnia treated in all respects exactly 
alike. If the acid solution is allowed to cool, it no longer 
acts characteristically w r ith the bichromate of potash or the 
other tests. Their action is w r holly destroyed or greatly 
impaired. Hence, in applying the colour-tests for strychnia, 
we must use concentrated pure sulphuric acid, and use it 
cold,. 
So much for the first part of the colour-tests. We add to 
the alkaloid under examination sulphuric acid in small quan¬ 
tity—pure, strong, and cold ; and it undergoes no change of 
colour. The alkaloid, therefore, whatever it may be, belongs 
to the class of which strychnia is one. 
