Certain vegetable infusions, especially inf. uvae ursi, inf. senegae, inf. scoparii, and inf. caryophylli, react with spt. aether, nit., and the nitric oxide eliminated plays the part of an oxygen-carrier, with the result that unexpected decompositions occur, gases accumulate in the mixtures, colours change, and bottles burst. This is due to reaction between tannin and nitrous ether, a statement which one investigator proved by detannating the infusion in mixture a before mixing with spirit of nitrous ether, when no decomposition occurred:

The stock mixture b gave no trouble on two occasions, but afterwards emitted nitrous fumes, blew out the cork, and formed a brown deposit. It is obvious from the nature of nitrous ether that in presence of an acid and vegetable matter of any kind changes such as these may be expected, whether tannin is present or not. Mixtures which are liable to evolve gases when bottled should always be made in a measure and not transferred to the bottle until effervescence ceases. If required to be delivered at once, the customer should be instructed to loosen the cork of the bottle on reaching home. To obtain uniform results in such mixtures it should be borne in mind that freshly made infusions must be used. Concentrated preparations of drugs such as cloves and broom, however well prepared, vary with different makers, and one make does not give the same results as another so far as appearance is concerned.

It frequently happens that chemical changes take place in mixtures which are quite unexpected by the prescriber and dispenser. Thus mixtures containing tr. nucis vom. and spt. ammon. arom. gradually become, as a rule, greenish blue in colour, this change being most probably due to the presence in nux vomica of a nuclein compound of copper. Igasuric acid (a constituent of the drug) also becomes green with ammonia, but copper only accounts for the blue colour (see C. & D. 1905, 11. 888 and 917). The change also occurs in mixtures of bismuth solution and tincture of nux vomica, and the following (a) becomes bluish violet in one day:

In a few hours b mixture becomes colourless, and throws down a considerable brown precipitate. If the bromide be omitted, the same change takes place, but the brown compound remains in solution instead of being precipitated. The change is due to the action of the ammon. carb. on the cochineal-colouring of the tr. chlorof. co. It may be noted that the alkaloid in liquid extract and tincture of nux is not so easily precipitated by alkalies as is liq. strych. (p. 291).

Tincture of nux vomica, owing to the igasuric acid which it contains, is very apt to change colour when mixed with nitric acid or nitro-muriatic acid. For instance:

If mixed in the order written, the mixture soon becomes yellow-coloured and acquires an odour of nitrous acid; if the order be reversed, neither colour nor odour is developed. Various results are produced by mixing part of the water with the acid and part with the tincture. A red or reddish-yellow colour develops in course of time, but is ultimately discharged. This applies particularly to nitro-muriatic acid and nux vomica mixtures. Somewhat analogous changes take place in the following mixtures:

No. I. became black in forty-eight hours, while No. II. assumed a colour almost like compound tincture of cardamoms in the same time. It is a matter of common observation that aqueous solutions of alkaline salicylates become of a reddish-brown colour on exposure to light, apparently due to the oxidation-products of salicylic acid being accompanied by coloured bodies. Stock solution of the bicarbonate induces the coloration more readily than the bicarbonate itself, owing to the solution containing carbonate. Natural salicylic acid and the physiologically pure artificial acid, and salicylates made from them, are not so liable to change. With impure salicylate the change is much more rapid; but the purest 'artificial'salicylate stands the test quite as well as that made from 'natural'salicylic acid. The coloration is still further postponed by using distilled water containing carbonic acid in solution (i.e., plain aerated water).1

No. III. mixture changes very rapidly, for in a few hours it is deep orange in colour, and a day after it is greatly intensified, finally becoming deep blackish brown. Sodium salicylate and spt. aether, nit. produce a red colour, forming nitro- and diazo-oxybenzoates of sodium, which do not seem to be harmful No. IV. has frequently been dispensed. Although the spirit was neutralised, the mixture rapidly coloured, and in a few hours it was of a brilliant deep orange tint. See also page 279.