Acacia is rarely prescribed per se in mixtures, and when it is it may be as either an emulsifying or a suspending agent. If the former, either the powder or the mucilage may be used, according to the nature of the substance to be emulsified ; if for suspending, use the mucilage. For making mucilage small picked gum ('Trieste grain,' it is called) is excellent. Allow it to macerate in the water till dissolved, aiding the solution by occasional stirring with a bone spatula. Strain through muslin. This mucilage will keep any reasonable length of time, and is remarkably clear and bright. Flake or scaled gum is also good.

An excellent plan for making and preserving acacia mucilage is to keep two wide-mouthed bottles- of capacity equalling two or three days' supply of mucilage- one with a tin cap to dispense from, the other corked for making, and labelled with the quantities of ingredients that will fill it; when filled, lay the bottle on its side in a drawer which is frequently opened and shut, then the gum soon dissolves. When the dispensing-bottle is empty, thoroughly cleanse it, strain the reserve supply into it, and start a fresh batch in the making-bottle. Five to 10 minims of formalin to the pint keeps mucilage for a long time.

Bismuth Salts

The subnitrate and salicylate readily give up part of their acid when treated with water, and the result is that unexpected difficulties sometimes occur which trouble the unreflective compounder. The salicylate may be entirely freed from salicylic acid by washing with alcohol or water.

Butyl-chloral Hydrate dissolves so slowly in water (its solubility is 1 in 50) that it is usual to expedite solution by heating. Care should be taken not to use water exceeding 1700 F. in temperature, otherwise the solution is opalescent and more acrid to the taste than when cold water is employed. Glycerin is the best solvent. Avoid alcohol, which forms insoluble butyl-chloral alcoholate.

Caffeine Citrate forms a clear syrupy solution with three times its weight of water, but on adding more water caffeine hydrate is precipitated, and does not dissolve until more than ten times the original amount of water has been added and the mixture well agitated. The salt is, therefore, easily dissociated.

Calamine for face-lotions should not have a pink colour. One of the best varieties has a tint which is undetectable on the skin.

Carbon Bisulphide B.P. has an odour resembling that of chloroform. A bad odour is due to excess of sulphur.

A little mercury kept in the bottle combines with free sulphur and keeps the bisulphide sweet without injuring the liquid. The bisulphide should be kept in opaque bottles away from sunlight in order to minimise decomposition.

Copaiba varies greatly in viscosity, some kinds being almost limpid. These should not be used for pill-making. The best copaiba for pills is the thick Maranham kind. Viscosity is inversely proportionate to the amount of essential oil in the copaiba.

Extract Of Belladonna

Dispensers should be careful in regard to what they give for this. Ext. belladonnae viride, B.P. 1898, is the extract made from the juice of the fresh plant, and varies in alkaloid from 0.5 to 2 per cent.; the B.P. 1914 replaced this with alcoholic extract of dried leaves, which is a powder containing 1 per cent, of alkaloid. The alcoholic root extract of the 1898 B.P. is no longer official, but is made extemporaneously from the liquid extract for the plaster.

Ferri Et Strychninae Citras

There are two commercial varieties of this, one green, the other brown. The former is preferred. It contains 1 per cent, of strychnine.

Ferrous Sulphate

A very small amount of sulphuric acid in aqueous solution of this salt serves to keep it bright and green. For pills the dried salt makes a better and less crumbly mass than the powdered crystals.

Gelatin, varies considerably in gelatinising-power, and compounders should always keep to the brand which they have found to meet their requirements, as a change may greatly alter the character of jellies, suppositories, and the like.