EXTRACTS FROM A LECTURE ON STRYCHNINE. 
607 
c. Sulpha cyanide of Potassium, a white precipitate. 
D. Per chloride of Mercury, a white precipitate. 
E. Perchloride of Gold, a lemon yellow precipitate. 
f. Chlorine Water, a white precipitate, which dissolves in ammonia to 
colourless liquid. 
g. Nitric Acid (cold), colourless solution ; (heat), yellow solution. 
h. Sulphuric Acid (with trace of Nitric Acid ) and Binoxide of Lead, a 
violet, changing to a red colour. 
i. Sulphuric Acid and Binoxide of Manganese, a violet, changing to a 
red colour. 
J. Sulphuric Acid and Bichromate of Potash, a violet, changing to a red 
colour. 
The tests a to g cannot be applied excepting where the quantity of 
strychnine at the command of the operator is considerable, so that in dilute 
solutions they fail to act. The remaining tests, h to j, are, however, much 
more delicate, and will indicate a most minute amount of strychnine. So 
far as my experience goes, I prefer the sulphuric acid and bichromate of 
potash test, as it is much more certain in its action, and is more delicate 
than any or all of the other tests. The colour indications are best seen in 
a pure solution of strychnine ; the presence of organic matter impedes the 
action of the test, and alcohol, acetic acid, and other bodies, entirely destroy 
the characteristic colour. In order to steer clear of these sources of error, 
Dr. Letheby has lately suggested that the substance to be tested should be 
treated with sulphuric acid, and placed on a piece of platinum foil connected 
with the positive pole of a galvanic battery, and thereafter, on touching the 
liquid with the negative pole of the battery, which terminates in a platinum 
wire, the characteristic violet tint is at once produced. In this way T5 jjooth 
of strychnine in pure water has been detected. I have repeatedly tried this 
process, and can bear witness to the accuracy of the test ; but in practice I 
have found the sulphuric acid and bichromate of potash to be a more deli- 
cate test, though it is much more difficult to manage. Lately a good deal 
has been said in disparagement of the colour tests for strychnine, and con- 
siderable doubt has been thrown upon the trustworthiness of colour tests in 
general. Precipitate tests are certainly more satisfactory than colour tests, 
because they signify the presence of a larger amount of the particular sub- 
stance under examination; but, in general, colour tests are far more deli- 
cate in their action than precipitate tests. A very good example of this 
occurs in testing for iodides. When these are abundant, precipitate tests 
with soluble salts of lead and mercury may be readily obtained ; but by 
dilution a point is at last reached when lead or mercury solutions cease to 
be precipitated by the liquid containing the iodide. At this point the starch 
test, which, in a very dilute solution of an iodide is essentially a colour 
test, comes into play, and long after the precipitate tests fail to indicate an 
iodide, the colour test shows unmistakable evidence of its presence. The 
same remark applies to testing for solutions of persalts of iron, and copper, 
by means of ferrocyanide of potassium. In strong solutions a blue pre- 
cipitate is indicative of iron, and a ruddy-brown precipitate speaks of copper ; 
but when dilute solutions are examined, blue and ruddy-brown colorizations 
are alone obtained. Colour tests, therefore, are the most delicate of all 
tests; they indicate the presence of a body when precipitate tests cannot 
do so ; and for my own part, I see no reason why I should distrust my 
sense of colour whilst manipulating in my laboratory, and confide in it at 
other times. 
I have now to refer to the action of strychnine on animals, with special 
reference to its subsequent detection in the animal system. At the begin- 
