Tinctura Nucis Vomicae

The fact that this preparation contains a trace of copper as well as igasuric acid has been mentioned (page 242). The tincture gives an opaque mixture with water owing to inert fatty matter being precipitated. Filtration is therefore permissible. A drachm of the tincture in an ounce mixture gives a diffusible precipitate of alkaloids with spt. amnion, arom. 3j., or liq. potassae mxx., or liq. ammon. mxx.

Vinum Ferri And Alkalies

If iron wine is properly made the following gives a precipitate of ferrous hydro-carbonate with the potash :

Some send out a mixture like this clear. A case was investigated, and it was found that the iron wine which had been used contained a mere trace of iron, and what there was in it was kept in solution owing to the presence of citrate of potash. Vinum ferri and liquor arsenicalis are sometimes prescribed together, the result being a repulsive-looking muddy mixture. Liquor arsenici hydrochlor. should be prescribed instead of the alkaline solution. The following example of this kind has been reported by Mr. Archibald Currie:

The first time the mixture was dispensed it was clear; on the second occasion it contained a green precipitate. Two different wines were used. On testing these a trace only of iron was found, and in the ferric condition, in No.1, while No. 2 contained 0.47 per cent in the ferrous state, with a trace of ferric. No. 1 was a year old, faintly acid, and was a rich, full-bodied, rather sweet sherry, while No. 2 was new, dry, and faintly acid. The precipitate in the mixture made with No. 2 consisted of a mixture of ferric and ferrous hydroxide.

Volatile Ingredients In Mixtures

Volatile substances should never be mixed with hot fluids. If a salt has to be dissolved in an infusion freshly prepared, or in hot water, either should be made quite cold before adding such things as ether, ammonia, or hydrocyanic acid; then cork quickly and shake thoroughly. Never put such volatile ingredients into an empty bottle and then fill up with water; put the water in first, leaving just room enough for the volatile ingredient- for two reasons: firstly, because the empty space in the bottle becomes charged with the volatile vapour, which is displaced when filling up; and, secondly, what is perhaps not often taken into Consideration, most of the vapour from the bottle being filled passes into the water-bottle used for filling it. For instance, in making a chlorine gargle one puts potassium chlorate and hydrochloric acid into an empty 12-ounce bottle, which rapidly becomes charged with chlorine-vapour. Now take a bottle containing 30 ounces of distilled water, and fill up the gargle. In so doing most of the 12 ounces of chlorine-vapour will pass into the water-bottle and contaminate the next thing the water-bottle is used for. A case is on record where a dispenser noticed iodine liberated in a bottle of medicine containing potassium iodide.

He could not account for it at all, but at last found that the water-bottle had just previously been used to fill up a mixture containing spirit, aether, nit., the vapour of which passed into the water-bottle, was absorbed, and carried into the next bottle of mixture, containing potassium iodide. Make it a rule that when a mixture is not made up to the required volume in a measure the requisite quantity of water should be placed in a measure and poured therefrom into the medicine-bottle.

Zinci Bromidum may be taken as typical of halogen salts of metals. Usually dispensers are apt to regard bromides as unchangeable or unprecipitable compounds. The following is an example of the error:

With one sample of sodium bromide this prescription gave a mixture with a flocculent precipitate of zinc hydroxide and carbonate, due to the presence of free alkali in the sodium bromide. A few drops of dilute hydrobromic acid sufficed to clear the mixture. A similar expedient may be adopted in other cases in which a metallic hydroxide is precipitated to a slight extent owing to traces of alkalies; but sometimes the addition of acid must anticipate precipitation, as there are hydroxides which do not redissolve readily once they are formed.