The remarks on solution (pages 56-61) specially apply to mixtures of saline substances. The general directions there given as to the formation of solutions should be followed in making mixtures. Three methods of procedure are commonly observed at dispensing-counters-(1) putting the salt to be dissolved into the bottle in which the mixture is to be dispensed and shaking with the solvent- this is the slovenly way, because it is always advisable to strain solutions into the bottle in which they are to be sent out; (2) dissolving in a solution-bottle or measure by agitation; and (3) in a mortar. This last is the poorest method, unless when hot water is the solvent, then a porcelain mortar may be used. Glass mortars or thick glass vessels should not be used for making solutions. When decoctions or infusions are ordered, the salt may be dissolved in them while hot, if the quantity of salt is not more than will remain dissolved in the cold solution. Carbonate of ammonium must be dissolved in the cold.

Nearly all salts dissolve to a greater extent in warm than in cold water (compare Page 59).

Many salts are more soluble if several are dissolved in the same vehicle, or if there is some acid present. Sulphate of potassium, for instance, is more soluble in a solution of sulphate of magnesium than in pure water. In such cases double salts are formed, which are more soluble than the separate constituents. In the case of 'Henry's Solution of Magnesia' the sulphuric acid makes the sulphate of magnesium dissolve in a smaller proportion of water than would otherwise be required.

The addition of tinctures, or other spirituous liquids, to a solution of a salt tends to throw the salt out of solution, because the mixture of spirit and water is not so good a solvent as water alone.

In this case much of the arsenate crystallises out in a few hours. When the prescription was received, it was suggested to the doctor that the liquor should be mixed with 1 1/2 ounce of water and then 1 1/2 ounce of spirit added, as this solution yields no crystals. The alteration was sanctioned. Of course, there are many substances, but few inorganic salts, which are more soluble in alcohol than in water.