2. Dissolve in water with a trace of acid, and divide on several watch-glasses, as described in the introduction. If one portion be cautiously tasted, and there be no bitterness, strychnia is very improbable.
3. Proceed at once to the colour test. Transfer a portion of the residue, dissolved in a drop of acetic acid, to a white porcelain dish or plate; dry gently on the water-bath; moisten it with about two drops of pure concentrated sulphuric acid; strychnia gives no coloration; with the point of a knife place a minute quantity of finely-powdered peroxide of manganese (the precipitated hydrate is often recommended, but the natural peroxide answers better, being more gradual in its action) on the side of the dish; slant the dish so as to allow the liquid to come in contact with the powder. At the moment of contact a deep rich blue colour is produced if 1/20000th of a grain of strychnia be present. The blue colour rapidly changes into purple, crimson, rich red-brown, then fades into bright orange-red, which last tint remains for some hours. By cautiously stirring with a glass rod, the succession of colours can be brought out again at another spot. One or two other qualified observers should always be summoned to witness the experiment, for two reasons; first, that they may testify at the trial, if necessary, to the certainty of the conclusion; secondly, because the sense of colour is differently developed in different people, and, if the hues are faint, one is apt to imagine what one expects to find. But if two or three, without prompting, see the same appearances, the chance of error is removed.
Applied in this way, the succession of colours is absolutely peculiar to strychnia. But, as objections have been made that these can be produced from other substances, they may as well be discussed and disposed of.
(a) Curarine (from Strychnos toxifera) has a bitter taste, is almost insoluble in ether and chloroform; hence it is not usually extracted by the above alkaloidal process, but remains behind in the aqueous liquid. With sulphuric acid and peroxide of manganese it gives the same colours as strychnia, but the changes are slower. With sulphuric acid alone, it yields a pale violet colour, changing to dirty red, and finally to rose. Its physiological effects are opposite to those of strychnia—so much so that it has been proposed as an antidote.
(b) Pyroxanthine (a rare substance, obtained in very small quantity from wood spirit), salicine (from the willow), and piperine (from pepper), give with sulphuric acid alone a deep-red colour, destroyed or spoilt by peroxide of manganese. (Nunneley, in Palmer’s trial.)
(c) If sugar and bile should be present together, sulphuric acid will develope a purple colour very like the strychnia test. Bile would also give bitterness. But it must be remembered that bile, without sugar, will not give the colour, that sugar will not be extracted by the ether-chloroform, and that the colour will appear immediately on the addition of the acid alone, whereas strychnia remains then uncoloured.
(d) Many resinous and saccharine matters are coloured by sulphuric acid, but can be got rid of by warming with the acid as described above.
So that none of these can be mistaken for strychnia. This important test depends upon the action of nascent oxygen; hence any substance which yields oxygen will give the colours more or less satisfactorily. Bichromate of potash, potassium ferricyanide, peroxide of lead, peroxide of cerium (Sonnenschein), have been employed, but most of them give colours of their own, and none are so good as peroxide of manganese. It is only necessary that the manganese should be finely pounded and not too much added. The action is slower and more lasting than with bichromate.
Letheby’s galvanic test is interesting, and has the advantage of not introducing any extraneous substance into the matter under examination, so that another alkaloid can be tested for afterwards. I have found it better to place the drop of supposed strychnia solution, acidified with a drop of dilute sulphuric acid (10 per cent. strength) on a white plate, to place on its opposite sides two small pieces of platinum foil pressed closely against the plate, touching the drop, and approaching within a quarter of an inch of one another, and to touch them simultaneously with the terminals of a battery of two Grove’s or other cells. In the region of the positive terminal the same colours manifest themselves as with peroxide of manganese. If no colour is shown at once, the battery should be removed, as further galvanic action may decompose any other alkaloid that may be present. The test is not so delicate as sulphuric acid and peroxide of manganese.