Elements of pharmacy, materia medica, and therapeutics / by William Whitla.

  • William Whitla
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: Elements of pharmacy, materia medica, and therapeutics / by William Whitla. Source: Wellcome Collection.

    77/656 (page 73)
    I making Spt. Ammon. FcBtid., or to separate impurities from ,1 the liquid which could not be got rid of otherwise. Distilla- 1 tion is a mixed process, consisting of ebullition—by which, in lithe first instance, the volatile substance is converted into f vapour—and of condensation, by which the vapour is again ;< changed into a liquid. i Destructive or Dry Distillation is the process by which j; a body is decomposed by heat into volatile products which did \ not previously exist in it, the products being collected in a i separate vessel, as in the production of acetic acid and tar : from wood. Fractional Distillation means the distilling of a mixture ; of substances volatile at different temperatures, whereby they : may be separated and received into different vessels by regu- I latin g the temperature. Drying is a process used in the preparation of a great many ] remedies. There are, however, no official directions given for : the drying of roots, leaves, seeds, &c.; these are generally sub- ; mitted to a uniform temperature, after being spread out on ! shallow trays or drawers of network, in a room, heated by 1 steam or hot water pipes. The best heat is one ranging between ' 100° and 130° F. Many plants which are used in Pharmacy are ; dried simply by exposure to the sunshine of their native country, but this is not practicable in our latitude. Flowers should be ' allowed to dry spontaneously. Fleshy roots should be trans^ versely sliced before being placed in the drying room. Crystals and precipitates, as a rule, stand higher temperatures, and may ! be dried on a water bath. Others require still higher tempera- tures, especially when we aim at the expulsion of the water of crystallisation, as in drying alum and sulphate of iron—where a heat of nearly 400° is required. On the other hand, some salts, like the valerianate of zinc, must be dried at the ordi- nary heat of the surrounding atmosphere. Carbonate of potas- sium and slaked lime recently heated are used to absorb the water from alcohol, freshly burned lime from ether, whilst sulphuric acid is used in various drying processes. Elutriation—The process of powdering rough insoluble substances like chalk, ores, &c., and mixing them with water, so that the finer, light, powdery portion may be poured off after the coarser particles have fallen to the bottom. It is done sometimes merely to wash away such impurities as sand, gravel, &c. ; in its results it resembles sifting. Expression is the process by which the juice or oil is squeezed out from vegetable substances, and the tincture or spirit from the marc after maceration or percolation. It is