Most of the medicinal glucosides undergo hydrolysis somewhat readily, especially when alcoholic preparations of them are mixed with water. Unexpected therapeutic results sometimes occur. For example, tincture of strophanthus in aqueous mixture becomes in a short time so changed as to set up intestinal irritation.

Glycerin is a useful and powerful solvent, acting at the same time as an antiseptic. It is largely used as a sweetening-agent in mixtures. It is the best and most appropriate solvent and preservative of the peptic and pancreatic ferments. Pill-masses containing a little glycerin do not harden, but care must be taken to avoid excess, as too much makes the pills hygroscopic. For dispensing it is best kept diluted with an equal volume of water, as then it is easily poured, and there is less loss from part of it remaining in the measure.

The following table shows the capabilities of glycerin as a solvent. It represents the weights in grains of the substances named which dissolve in 1 fluid ounce of glycerin sp. gr. 1.260, heat being used to promote solution:

Solution is not effected quickly in pure glycerin, as its thickness prevents diffusion, which is necessary in practice. Glycerin solutions which are used as topical applications have given results obtainable by no other preparations of the same active constituents, but recent observations have proved that these are due to the glycerin itself, which stimulates the osmotic process in cellular tissue, and so relieves congestion. The use of glycerin suppositories and injections for constipation is a familiar example of this.

Iodine dissolves in water only slightly, but is freely soluble in aqueous potassium-iodide solution. It is soluble in alcohol, ether, chloroform, carbon bisulphide, glycerin, and fixed and essential oils. With fixed oils it chemically combines to a small extent, also with essential oils, and some care should be observed in mixing it with the latter or their alcoholic solutions. Free iodine is not often given internally, but if it occurs in a prescription for an aqueous mixture without any solvent see the prescriber, and suggest the addition of sufficient potassium iodide to dissolve the iodine.

Manna is rarely required in solution in English practice, but in continental dispensing it is more needed, especially in Germany. Direct heat should never be applied to effect its solution. Allow the manna to macerate in just as much cold water as will change it into a soft pasty mass; then add the rest of the water required and dissolve by a gentle heat. Strain through fine muslin. Squire recommends manna to be purified by dissolving it in as little water as possible, straining, and evaporating to the original weight. Manna is sometimes given along with magnesium sulphate in mixture; in this case beat up the manna with the sulphate, then add the water and dissolve.

Morphine Salts should be dissolved without heat, for at a temperature above 1040 F. (400 C.) their solutions are apt to turn yellowish or even brown. With care beautiful solutions may be made. Morphine meconate is least affected by heat, but the solution of this salt should only be filtered through paper which has previously been washed free from iron by means of hydrochloric acid and water, otherwise the solution will be coloured red. The following are the better-known salts of morphine and their solubility in water at 6o° F. (15.5° C.):

Acetate [B,C2H4O2,3H2O], i in 2 1/2 Hydrobromide [BHBr,2H2O], 1 in 25 Hydrochloride [B,HC1,3H2O], 1 in 25 Lactate [BC3H6O3], 1 in 8 Meconate [B2C7H4O7,5H2O], 1 in 40 Oxalate [B2C2H2O4,H2O], 1 in 20 Sulphate [B2H2SO4,5H2O], 1 in 21 Tartrate [B2C4H6O6,3H2O], 1 in 11

In these formulae B stands for the morphine molecule C17H19N03. Morphine acetate is the least stable of the salts of the alkaloid, and the tartrate is best for hypodermic solutions because it is stable and exceptionally soluble.