For general dispensing-purposes triturations of arsenic, strychnine, sodium arsenate, mercuric chloride, etc, are very useful. Lightly triturate one part of the medicament with an equal weight of coarse sugar of milk until thoroughly mixed, then with firmer pressure until an impalpable powder is produced ; next add gradually 8 parts of fine sugar of milk, and continue trituration until uniform, occasionally detaching all powder adhering to the mortar and pestle. Transfer to a bottle, and label distinctly with the name of the medicament on one line, and below it 'Trituration 1 in 10.'

Percentage Solutions sooner or later become a problem to the dispenser or student, on account of differences of opinion about what they are and complications between our weights and measures.

The percentage solutions employed in chemical or other scientific research are solutions containing a known weight of the dissolved substance, called the 'solute,' in a definite weight of the solvent; thus a 5-per-cent. aqueous solution of borax is made by dissolving 5 grammes of borax in 95 grammes of water, or if glycerin is the solvent, 95 grammes of glycerin is taken. It follows that the volume strength of these scientific solutions varies according to the density of the solvent; thus the aqueous borax solution contains 5 of borax in about 100 by volume, and the glycerin solution 5 of borax in about 80 by volume. These are not the solutions required at the dispensing-counter- in fact, they are used in research, and only when all quantitative determinations are made by weighing so as to be independent of the volume changes induced by variations in temperature and atmospheric pressure. Medicinal percentage solutions are (in English-speaking countries) a definite weight or volume of the solute in a known volume of the finished solution.

For example, a 1-in-1,000 solution of mercuric chloride would mean 1 gramme of the salt dissolved in sufficient solvent - say, water- to make 1 litre (1,000 c.c), or 1 ounce dissolved in sufficient water to make 50 pints (1,000 oz.); but if we weigh the mercuric chloride in grains the operation becomes confusing because the minim is not the equivalent of a grain in the sense that the c.c. is the equivalent of the gramme and the oz. of the fl. oz. It is necessary to bear in mind that 1 grain in 100 minims is not a 1-per-cent. solution, but 1 in 91, and 1 grain in no minims is approximately 1 per cent.

In preparing percentage solutions at the dispensing-counter in quantities so small that the avoirdupois ounce is inadmissible, the dispenser's easiest plan is to use metric weights and measures; otherwise grains and measures in the proportions mentioned. Thus 4 1/2 grains of mercuric chloride in 10 ounces of water is a 1-in-1,000 solution- not strictly so, but sufficiently near for surgical purposes, although a pharmaceutical examiner might not pass it. The British Pharmacopoeia 1-per-cent. solutions are made by dissolving 1 gramme of the solute in sufficient solvent to make 100 mils, of the solution (i.e., 17 1/2 grains in 4 fluid ounces). Students are particularly cautioned to master the percentage problem. At examinations, as well as in every-day practice, prescriptions are occasionally seen which are apt to confuse. See the specimen examination prescriptions at the end of this book.

There is, however, an exception to the rule- namely, when the solutions are to be administered by minims. This is especially the case with hypodermic injections, which are generally given in minims, and physicians who order 1-in-10, 1-in-20, 1-in-100, etc, solutions of this kind reckon that they are to get the unit of weight in the specified number of minims. These give no trouble at the dispensing-counter, except when large quantities have to be made up; then the following table will be useful:

It is to be expected that the British Pharmacopoeia, 1914, will make dispensers more familiar in practice with metric weights and measures, in which case strength of solutions will be grammes of solids (c.c. or mils, of liquids) in c.c. or mils, of the finished solution; but care must always be exercised in regard to the prescriber's intention or the purpose of the solution- i.e., whether the minim has to be considered or not. See p. 554 for a useful table of factors for solutions from 1 in 2 to 1 in 1,000.