48.2 
COLOUR-TESTS FOR STRYCHNIA, ETC. 
in no way interferes w ith the full development of the strychnia 
colours : and even the acid mixtures of the other colour- 
7 
developing tests are not open to any fallacy if the alkaloid is 
brought into contact with them as soon as they are made, and 
before the colours first produced are deepened or changed by 
exposure to the air. But the method of procedure which be¬ 
gins with dissolving the alkaloid in the acid and then apply¬ 
ing the colour-developing tests is to be preferred, inasmuch as 
the absence of colour in the acid solution is some advantage 
in itself, as giving full effect to the strychnia colours, while 
it has the still greater advantage of distinguishing strychnia 
from several alkaloids (poisonous and non-poisonous), which 
yield colours with the acid without the addition of the colour- 
developing substances. 
3. The best form in w 7 hich to apply the colour-tests for 
strychnia is a subject of considerable practical importance,, 
and it is one upon which there is at present no distinct agree¬ 
ment among chemists. Some authorities prescribe the appli¬ 
cation of the colour-developing substances in the solid form, 
some in solution ; and some who prefer the state of solution 
use strong solutions, while others employ weak ones. The 
balance of authority is certainly in favour of applying the 
colour-developing tests in the solid form, and my own ex¬ 
perience is favorable to this mode of application. It is also 
commended by the obvious consideration that solution in water 
is favorable to a rapid development of the changing colours 
which constitute the test, such quick change of colour being 
among the most serious objections to the colour tests. At 
any rate it must be admitted to be of the first importance to 
secure as slow 7 a change of colour as possible, in order to 
give time for the observation of the colours actually produced. 
The superiority of the solid form to the solution is easily 
show n by a comparative experiment. If w r e take tw T o minute 
fragments of bichromate of potash of equal size, place them 
on a slab of white enamelled glass or porcelain, add to one of 
the fragments a drop of distilled water, and dissolve it in the 
water, and leave the other untouched, then place on the slab 
two equal drops of the same solution of strychnia in sulphuric 
acid, we shall find that on bringing the fragment of bichro¬ 
mate of potash into contact with the acid solution of strychnia, 
its colour changes from yellow to blue, and, w r hen stirred into 
the liquid with a glass rod or glass spatula, yields a rich blue 
solution, which retains this colour long enough for easy and 
complete identification, and then gradually assumes the 
other tints to be presently described, retaining the final tint 
for hours or days. While, on the other hand, the solution of 
