COLOUR-TESTS FOR STRYCHNIA, ETC. 
731 
must know that failures rarely, if ever, occur, whatever the 
mode and form of application of the tests. But it should be 
borne in mind that for class purposes it is usual to employ a 
quantity of alkaloid much exceeding the two-hundredth of a 
grain contained in the drop of acid as used in the experiments 
1 have been describing. Even with this small quantity of 
strychnia, solutions of three soluble tests—bichromate of 
potash, ferricyanide of potassium, and permanganate of potash 
—in the proportion of ten grains to the ounce of distilled 
water, give rise, with occasional exceptions, to such a distinct 
development of the first colour as to leave no doubt of the 
presence of strychnia, though the after colours were fleeting, 
variable, and wanting in distinctness. These experiments, 
then, justify the use of the colour-developing tests in solution 
as tests for strychnia, but it may admit of doubt whether in 
medico-legal cases we should be so fortunate as to deal with 
quantities of strychnia large enough to yield characteristic 
results with the reagents in a state of solution, however con¬ 
centrated. I am of opinion, from the experiments I have 
detailed, as well as from the more general results of my expe¬ 
rience of the strychnia-tests, that for medico-legal purposes 
the colour-developing reagents should always be added to the 
acid solution of the supposed alkaloid in substance, and not 
in solution. 
My conjecture, that the success of class experiments in 
which the colour-developing tests are used in solution, 
depends on the use of a larger quantity of strychnia than the 
two-hundredth of a grain, was confirmed by actual trial; for 
I found that with these larger quantities, the tests in solution 
developed the same characteristic colours, or very similar 
ones, as those brought out by the same tests in substance. 
2. The second question, namely, Of the colour-tests for 
strychnia , which is to be preferred ? cannot be properly discussed 
without some preliminary inquiry into the true meaning of 
the colour-tests, and some description of the succession of 
colours which constitute those tests. 
The colours produced by the action of the peroxides of 
manganese and lead, the bichromate of potash, the ferri¬ 
cyanide of potassium, and the permanganate of potash, on a 
solution of strychnia in strong sulphuric acid, are usually 
described as deep blue, passing to violet, purple, and red, 
and, after long exposure, passing to light red. 
This description of the colour-tests is sufficiently faithful 
for every practical purpose, and it applies to all the colour- 
tests, and to all specimens of strychnia of the usual purity. 
It admits, however, of being simplified with advantage by 
