COLOUR-TESTS FOR STRYCHNIA, ETC. 289 
tests, I had no hesitation in selecting the peroxide of lead as 
the better of the two insoluble tests. 
The experiment with the three soluble tests was conducted „ 
in the same manner with three rows of twenty slabs each, and 
it issued in showing the superiority of the permanganate of 
potash over the bichromate of potash and the ferricyanide of 
potassium in the richness and clearness of the first and most 
characteristic tint. The subsequent colours were also clearly 
brought out. But the permanganate of potash resembled 
the bichromate of potash in exhibiting less permanency in 
the third tint than did the ferricyanide of potassium. It 
resulted from a careful comparison of these three tests that 
the permanganate of potash is to be preferred to the other 
two. 
There remained, therefore, to be submitted to a further 
comparative experiment the peroxide of lead, as the better of 
the first group of two, and the permanganate of potash, as 
the best of the second group of three. 
The comparative experiment for this purpose was the exact 
counterpart of those just described. Twenty experiments 
with the peroxide of lead were compared with twenty similar 
experiments with the permanganate of potash. The result 
was decidedly in favour of the permanganate of potash, which 
gave in every case a clear, rich blue colour, while the colour 
with the peroxide of lead was less clear and bright, being 
sometimes obscured by the colour of the portions not dis¬ 
solved. In two of the experiments the result was not 
satisfactory. 
I repeated these comparative experiments with several stains 
left by the evaporation of solutions of strychnia in benzole, 
and found the permanganate of potash to yield characteristic 
results where the peroxide of lead failed. I estimated the 
quantity of strychnia in these stains at less than the thousandth 
of a grain. The permanganate of potash acted character¬ 
istically in every instance. 
Having thus ascertained the superiority of the permanga¬ 
nate of potash to the peroxide of lead, I made a final experi¬ 
ment with the three soluble colour-developing substances; 
the permanganate of potash, the ferricyanide of potassium, 
and the bichromate of potash. I took eighteen glass slides 
stained with deposits of strychnia, some from the solution of 
the alkaloid in benzole, and others from a solution of the 
acetate decomposed by the vapours of ammonia. I arranged 
the eighteen stains in groups of three, putting those of equal 
size together, and I noted the results at once by the position 
of the slides. All the spots were first treated with a single 
