Chemistry : general, medical, and pharmaceutical including the chemistry of the British Pharmacopœia a manual on the general principles of the science, and their applications in medicine and pharmacy / by John Attfield.

  • John Attfield
Date:
1881
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry : general, medical, and pharmaceutical including the chemistry of the British Pharmacopœia a manual on the general principles of the science, and their applications in medicine and pharmacy / by John Attfield. Source: Wellcome Collection.

    742/850 (page 708)
    ^08 SILICATES. Silica (SiOo) may be separated from alkaline silicates, or from silicates decomposable by hydrochloric acid, by digesting the substance in hydrochloric acid at a temperature of 70° or 80° C. nnbil completely disintegrated, evaporating to dryness, heating in an air-bath, again moistening -with acid, diluting with hot water, filtering, washing, drying, igniting, and weigh- ing. ESTIMATION OP WATER. Water and other matters readily volatilized are most usually estimated by the loss in weight which a substance undergoes on being heated to a proper temperature. Thus, in the British Pharmacopoeia, crystalline gallic acid (H3C7H3O5, H3O) is stated to lose 9'5 per cent, of its weight at a temperature of 100° C, oxalate of cerium (OeCjO^, 3HoO) 52 per cent, on incineration, cai'bonate of potassium about 16 per cent, on exposure to a red heat, sulphate of quinine (2C2oH2^]Sr202, H2SO4, 7H3O) 14'4 per cent, at 100° C, arseniate of sodium (NajHAsO,^, 7H3O) 40-38 per cent, at 149° C, carbonate of sodium (Na3C03, IOH2O) 603 per cent., phosphate of sodium (Na2HP04, I2H2O) 63 per cent., and sulphate of sodium (NajSO^, IOH3O) 65'9 per cent, at a low red heat: oxide of bismuth heated to incipient redness is not to diminish in weight. Frocess.—One or two grammes of substance is sufiBcient in experiments on desiccation, the material being placed in a watch-glass, covered or uncovered porcelain crucible, or other vessel, according to the temperature to which it is to be ex- posed. Rapid desiccation at an exact temperature may be eflPected by introducing the substance into a tube having somewhat the shape of the letter U, sinking the lower part of the tube into a liquid kept afc a definite temperature by aid of a ther- mometer, and drawing or forcing a current of dry air slowly through the apparatus. Substances liable to oxidation may be desiccated in a current of dried carbonic acid gas. The