The London dispensatory : a practical synopsis of materia medica, pharmacy, and therapeutics : Illustrated with many useful tables, and woodcuts of the pharmaceutical apparatus / by Anthony Todd Thomson ; edited by Alfred Baring Garrod.

Date:
1852
Catalogue details

Licence: Public Domain Mark

Credit: The London dispensatory : a practical synopsis of materia medica, pharmacy, and therapeutics : Illustrated with many useful tables, and woodcuts of the pharmaceutical apparatus / by Anthony Todd Thomson ; edited by Alfred Baring Garrod. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    68/1284 (page 52)
    fixed substance with which it was combined, evaporation is only employed where the liquid is of little value, such as water; but where a solid is to be recovered from a more valuable liquid, as al- cohol, for instance, the process of distillation is employed. For small processes, very good evaporating dishes are made of the bottoms of broken retorts and matrasses, which may be cut smooth round the edges by means of a hot iron or ring, d, with a wooden handle, e; and thus they are converted into semiglobular basins.1 The best evapo- rating dishes, however, are those made of porcelain, as Wedgwood’s, Berlin, and Meissen ware, and sold in assortments, the largest of which is capable of holding eight or ten pints. They are flat-bottomed, shallow vessels, f, with a lip, g, glazed in the inside; and thin, but of a dense hard texture. They will bear to be heated to the boiling point over a clear hot fire: but are apt to crack when a flame is allowed to play on them, or when the liquor is boiled to dryness, at the moment when the last drop of fluid is expelled, unless the fire be much lowered. It is preferable, therefore, when glass or earthenware vessels are employed, to apply the heat by the medium of sand ; or if a still more moderate heat be necessary, by means of boiling water, over which the evaporating dish should be placed. The first is denominated a sand bath ; the second, a water bath ; but for processes on a large scale, shallow iron pots or leaden troughs are used, to which the fire is directly applied. Exsiccation is a variety of evaporation, producing the expulsion of moisture from solid bodies by means of heat. It is generally employed for depriving salts of their water of crystallization. They are exposed to the action of a fire in an iron ladle or pot, or in a glass vessel; and after dissolving, as they are heated, in the water they contain, or undergoing what is termed the watery fusion, the water boils; and, evaporating, leaves the salt in the form of a dry mass. When the substances to be exsiccated are liable to decomposition in a temperature above 212°, as is the case with some of the compound oxides, and the alkaloids, the process must be conducted by the heat of a water bath. In delicate operations, exsiccation is performed in vacuo. This is one of the improvements of modern times, for the formation of extracts. Distillation differs from evaporation only in the circumstance, 1 The iron ring for this purpose is made red-hot in the fire, then put upon the matrass which is to be cut; and, when the glass is sufficiently heated, by throwing on it a little cold water, it will generally break exactly at the circle heated by the