This salt, as may have been noticed from many of the difficulties previously exemplified, is one of the most active chemical reagents, and as it is now extensively employed as an antiseptic, dispensers must bring all their chemical knowledge to bear upon it when compounding it.

With tr. iodi decol., B.P.C., a few months old No. I. gives a clear mixture. Sometimes there is a white precipitate. No. II. is for application to the scalp, the fine precipitate of ammoniated mercury being desired.

Cocaine and its Salts are now so commonly used for producing local anaesthesia that prescribers sometimes add a cocaine salt as an adjunct to caustic or irritating substances whose specific action on the skin or mucous membrane they desire. In consequence incompatibility results frequently. The following are examples:

Fiat collyrium.

Probably the prescriber knew that if he used cocaine hydrochloride there would be a precipitate of lead chloride. The plan with above is to dissolve the cocaine (diffused in a drachm of water) in a sufficiency of acetic acid carefully added.

Fiant guttae pro oculis.

Many more prescriptions with the same incompatibility might be given. They are common. The borax precipitates cocaine hydrate, which rapidly crystallises. Dissolve the borax in the rose-water, and add boric acid until the reaction is distinctly acid, then mix with a solution of the cocaine salt.

On dissolving the cocaine hydrochloride in 1ounce of water, the glycerin in 6 drachms,and adding the latter to the former, a precipitate was produced. Spring-water was used, but a clear solution was obtained with distilled water. Carbolic acid gives a milky mixture with solution of cocaine hydrochloride in distilled water, but no apparent precipitate.

Fiant guttae.

A white precipitate is formed consisting of chloro-hydrargyrate of cocaine. This is one of the B.P. tests for cocaine. The precipitate cannot be avoided.

M. 'The paint for the throat.' Silver chloride is precipitated. To avoid it, dissolve 21 grains of cocaine hydrochloride in 2 ounces of water, add, with constant stirring, ammonia solution to faint alkalinity, collect the precipitate on a paper filter, wash with 1 ounce of water, transfer the moist precipitate to a glass mortar, and dissolve with dilute nitric acid added drop by drop. Then proceed sec. art.

Fiat pigmentum.

This gives a white precipitate of cocaine hydrate, apparently owing to dissociation of zinc chloride, although the solution is neutral. A clear solution is obtained by dissolving the zinc chloride in water, clearing the solution with dilute hydrochloric acid, adding the glycerin, mixing well, then adding the cocaine salt dissolved in the rest of the water.

Some difficulty was experienced in getting a clear solution. The following procedure produced the best result: Dissolve the phenol in the glycerin; let the iodine and iodide stand with 0.6 gramme of water till solution is complete, then mix with the phenol and glycerin; place the cocaine hydrochloride in a mortar, and triturate thoroughly with a little of the mixed solutions, then gradually add the remainder, continuing the trituration steadily while the addition is proceeding.