The London dispensatory, containing: I, the elements of pharmacy; II, the botanical description ... and medicinal properties, of the substnaces of the materia medica; III, the pharmaceutical preparations and compositions of the London, Edinburgh, and Dublin Colleges of Physicians ... a practical synopsis of materia medica, pharmacy, and therapeutics : illustrated with many useful tables and copper-plates of pharmaceutical apparatus / by Anthony Todd Thomson.

Anthony Todd Thomson

Date:: 1818

Credit: The London dispensatory, containing: I, the elements of pharmacy; II, the botanical description ... and medicinal properties, of the substnaces of the materia medica; III, the pharmaceutical preparations and compositions of the London, Edinburgh, and Dublin Colleges of Physicians ... a practical synopsis of materia medica, pharmacy, and therapeutics : illustrated with many useful tables and copper-plates of pharmaceutical apparatus / by Anthony Todd Thomson. Source: Wellcome Collection.

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distances, and in the direct ratio of the quantity of matter, and the inverse one of the square of the distance, it is named gra¬ vitation : but when its operation is confined to the minute atoms of bodies, and is exerted only when these are near to each other, or in apparent contact, it is denominated con¬ tiguous attraction. The former preserves the planets in their orbits, and sustains in their places all the parts of the magni¬ ficent frame of the universe: the second is the cause of the regular figures of natural bodies, and of the various combina¬ tions of matter, which take place in and on the surface of our globe. It is this variety that we are here to examine. Contiguous attraction, operating on particles of the same kind, forms an aggregate or mass; and hence, the power in this instance is named the attraction of aggregation or cohe¬ sion : but acting on dissimilar particles, and producing bodies possessed of new properties, different from those of their com¬ ponents, it constitutes chemical attraction, or affinity* a, OF COHESION. The attraction of cohesion is that power which retains together the particles of bodies at insensible distances. Ac¬ cording to the degree of force which it exerts, substances assume the solid, the fluid, or the aeriform state. 1. In solid bodies this force is sufficiently powerful to prevent their com¬ ponent particles from being moved with regard to each other, except in a very small degree; and to oppose a considerable resistance to any mechanical power applied to separate them. In the same kinds of bodies, all the circumstances being equal, it is alwrays the same; but in dissimilar bodies it is exceedingly various: from which, and the peculiar arrangement of the particles, arise the different qualities of solids, denominated hardness, softness, malleability, ductility, and elasticity. The attraction of cohesion in solids is exerted at insensible distances only, and may be weakened or altogether overcome by caloric, or that matter which produces the sensation of heat. If a piece of ice, for example, be brought near a fire, the cohesion of its particles is weakened as the caloric flows into it, till it is changed from the solid state to the fluid, or water; and by continuing and increasing the heat, the particles are still further separated from each other, until the fluid passes into the gaseous form, or becomes steam. This power is also weakened by chemical affinity ; as when a solid body is put into a fluid, the affinity between the particles of the fluid and those of the solid is often sufficient to overcome the aggregation of the solid; and its detached particles being uniformly dif¬ fused through the fluid, now form a part of it, without altering either its fluidity or transparency. This constitutes the ordi¬ nary chemical or pharmaceutical process of solution, which ife

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