Pharmacologia / Fourth American, from the Seventh London Edition

by John Ayrton Paris

In rubbing together different substances, it is necessary to remember that there are many saline bodies, which in the dry state become moist and even liquid, by triture with each other, and that, under such circumstances, they are susceptible of mutual decomposition. This change is effected by the action of water, derived from the following sources.

1. From the water of crystallization. This always operates when the proportion contained in the original ingredients is greater than that which the products can dispose of; that is to say, whenever the capacity of the new compound for water is less than that of the original ingredients. By previously driving off this water by heat, we shall of course avoid such a source of solution, and no liquefaction can ensue. Thus, if recently burnt quick-lime be triturated with calomel, the resulting mixture will be white, shewing that no decomposition can have arisen, but add a few drops of water, and it instantly assumes a dark aspect. If crystallized sulphate of copper be triturated with Acetate of lead, the resulting mixture will assume a fine green colour, but if the sulphate of copper be previously heated, and its water of crystallization driven off, no change of colour will be produced; if, for Acetate of lead, we substitute muriate of lime, and the sulphate of copper be crystallized, we shall obtain a result of a yellow colour, but if the sulphate of copper be anhydrous, the product will be colourless, becoming however instantly yellow, like the former, on the addition of a drop of water; and on a further addition of this fluid, the yellow product in both instances will be rendered blue; which proves that a chemical decomposition has taken place, and a muriate of copper resulted; for this salt is rendered yellow by a small, and blue by a larger proportion of water. The Cuprum Ammoniatum presents another illustration, for the ingredients, when rubbed together, become extremely moist, and undergo a chemical decomposition. Certain resinous bodies also, as myrrh, become liquid by triture with alkaline salts, in which case the resin and alkali form a soluble compound, which the water of crystallization, thus set at liberty, instantly dissolves.

2. From aqueous vapour in the atmosphere. The water of the atmosphere does not act upon these occasions, unless it be first attracted and absorbed by one of the triturated bodies; e. g. if Acetate of lead and recently burnt alum be triturated together, no change will be produced; but, if the burnt alum be previously exposed for a short time to the atmosphere, these bodies will, in that case, become liquid.

The physician, without this chemical knowledge, will be often betrayed into the most ridiculous blunders, an instance of which very lately came to my knowledge in a prescription for the relief of cardialgia and constipation, in the case of dyspepsia; it directed sulphate of soda and carbonate of potass, in the form of a powder, but the fiat of the physician, upon this occasion, only served to excite the ridicule of the dispenser, who soon discovered that the ingredients in his mortar dissolved into liquid.

During the exhibition of powders containing insoluble matter, it is always important to maintain a regularity in the alvine excretions, or an accumulation may take place attended with very distressing symptoms. Dr. Fothergill relates a case of this kind which succeeded the use of powdered bark; and Mr. E. Brande has communicated a similar instance of mechanical obstruction, produced by the habitual use of magnesia. I could also add, if it were necessary, some striking facts of a similar tendency, which occurred from eating bread that had been adulterated with pulverized felspar. The precaution seems more particularly necessary in the case of children, whose bowels are very impatient of extraneous and insoluble contents.[^[296]] The dose of a powder ought not to exceed ʒj; and, when taken, should be diffused in water, wine, or any other convenient liquid; resinous and metallic powders require a thick and consistent vehicle, as syrup or honey, since they subside from those which are more fluid.

PILULÆ. Pills.

These are masses of a consistence sufficient to preserve the globular form, and yet not so hard as to be of too difficult solution in the stomach. The subject offers some extremely interesting points of inquiry. The following general rules will enable the practitioner to select those substances to which the form of pill is adapted, and to reject those to which it is not suitable, as well as to direct, extemporaneously, the most efficient mode of preparation.

I. The Selection of Substances.

1. Suitable Substances are, 1, All remedies which operate in small doses, as Metallic Salts; and 2, Those which are designed to act slowly and gradually, as certain Alterative Medicines, or 3, which are too easily soluble when exhibited in other forms, as Gamboge, &c. 4, Substances which are not intended to act until they reach the larger intestines, as in pills for habitual costiveness; see Aloes. 5, Bodies whose specific gravities are too considerable to allow their suspension in aqueous vehicles. Efflorescent salts may also be exhibited in this form, but they ought to be first deprived of their water of crystallization, or the pills composed of them will crumble into powder as they dry.

2. Unsuitable Substances are, 1, Those which operate only in large doses. 2, Which deliquesce. 3, Whose consistence is such as to require a very large proportion of dry powders to afford them a suitable tenacity, as oils, balsams, &c. 4, Substances that are so extremely insoluble, that when exhibited in a solid form they pass through the canal unaltered, as certain extracts.