Alkaloids

A knowledge of the ordinary alkaloidal reactions is very useful at the dispensing-counter. The following are fair examples of the cases in which this knowledge may be turned to practical account:

There is no precipitate in a if sodium bicarbonate is used and not old dispensing solution, but in any case a trifling amount (compare page 42). On the addition of liq. strych-ninae to b, the mixture assumes a yellow colour. Strychnine and other alkaloids are precipitated by alkaline iodides, and especially by mercuric iodide (a solution of which in potassium iodide and water is known as Meyer's alkaloidal reagent). The precipitate in this case is an iodo-hydrargyrate of strychnine, resulting from interaction between the strychnine hydrochloride and the arsenium and mercuric iodide of the Donovan's solution. Such precipitates are heavy, and in consequence dangerous, as the last dose in a bottle may contain nearly all the toxic alkaloid originally put into the mixture.

Ammonium Benzoate

The commercial salt is sometimes unduly acid and difficultly soluble; if so, it should be neutralised with a little ammonia. It is soluble in 6 parts of water.

Ammonium Bromide and sodium nitrite in aqueous solution interact when warmed, and the ammonium nitrite formed splits up into nitrogen and water. The interaction does not occur with potassium or sodium bromide, either of which should replace ammonium bromide in such mixtures. {C. & D., 1914, 1. 552.)

Ammonium Carbonate should always be dissolved in the cold, never with hot water. Only translucent pieces should be used at the dispensing-counter, never the effloresced salt or pulv. ammon. carb., which are deficient. It keeps fairly well in solution, and in dispensaries where a supply can be used up within three days a 1-in-8 solution may be stocked.

Borax

The peculiarities of borax are discussed later, in the chapter on Applications (page 343). It is most used externally. The following prescription is of interest in this section as being for a mixture and having created a lively correspondence in The Chemist and Druggist, August to October, 1898:

According to the British Pharmacopoeia the aqueous solution of gum acacia 'forms with solution of borax a more or less translucent white jelly.' A pharmacist who dispensed the above prescription obtained a jelly, but on communicating with the prescriber, a sample of a limpid mixture was sent. On publication of the prescription in The Chemist and Druggist, a number of correspondents sent in mixtures which were more or less limpid, these being obtained by diluting the mucilage to the fullest possible extent before adding a solution of the borax and sodium bromide in warm water. Mr. W. Martindale sent us a pourable mixture made in this way; but the original correspondent, following his directions, could only get a jelly with fresh mucilage, a pourable mixture with mucilage from the same gum not quite fresh, and a limpid mixture with cheap gum. Our own experience is that if made from a gum acacia strictly answering the Pharmacopoeia tests, the mixture cannot be made limpid, but with old and acid mucilage of any gum a limpid mixture results.

It will be observed that borax is in excess of the solubility-point, and some of it crystallises out.