Royle's manual of materia medica and therapeutics : including the preparations of the British pharmacopoeia and other approved medicines / by John Harley.

  • Harley, John, 1833-1921.
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: Royle's manual of materia medica and therapeutics : including the preparations of the British pharmacopoeia and other approved medicines / by John Harley. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    35/856 (page 23)
    DESICCATION—SPECIFIC GRAVITY. results, to keep the alkali always in excess, and this is done hy adding the former to the latter. _ In testing the characters and in ascertaining the purity ot drugs, the occurrence of a precipitate, and its natui'e and beha’^our with the precipitant or some other reagent, is the usual means of determining these questions. The preci- ]iitate rarely has a crystalline form, but this is the case with triple phosphate, oxalate of lime, and acid tartrate of potash. 11. Desiccation (tZesicco, to dry). Some salts and preci- pitates {e.g. Valerianate of zinc) must be dried at the ordinary temperature of the air. The greater number are not decomposed at 212°; and as it is desirable to dry cer- tain of them as rapidly, and wdth as little exposure to the ail’ as possible, a steam closet, fig. 12 (c is a little reservoir by means of which, as in fig. 7, p. 19, water is supplied to take the place of that lost by evaporation at /, and the fluid is maintained at the same level by the supply and waste pipes) should be used for this purpose. Deliquescent crys- tals may be formed, or dried over a dish of sulphuric acid, and enclosed under a glass shade, the edge of which is ground, and retained in air- tight contact with a plate of glass upon which it rests, by means of a little lard. Liquids are deprived of moisture by the following hygroscopic substances ; freshly burnt lime, dry carbonate of potash (see Alcohol), fused chloride of calcium (see .(Ether), and sulphuric acid. Gases are dried by allowing them to pass through a tube (fig. 13), containing fragments of fused chloride of calcium (a), or of pumice stone moistened with sulphuric acid (6). 12. Specific Gravity or Density.—By this is meant the w’eight of any substance as compared with the weight of an equal bulk o f a s tandard body. Equal bulks of different bodies differ much in w’eight, as, for instance, lead and cork, in consequence of the former containing more