Applied medical chemistry : a manual for students and practitioners of medicine / by Lawrence Wolff.

  • Wolff Lawrence.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: Applied medical chemistry : a manual for students and practitioners of medicine / by Lawrence Wolff. 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.

    23/220 (page 17)
    were to chemically alter the precipitate, that it would be unable to be longer held in solution, the effect would be chemical, as by the addition of amnionic hydrate to the above mentioned solution of mercuric nitrate. According to their character the precipitates are termed respectively crystalline, amorphous, flocculent, gelatinous and curdy, or if slight and held lightly in suspension and causing turbidity, or if sufficient only to impart a pearly light, as opalescent. Filtration and Decantation, Desiccation and Weigh- ing of Precipitates.—Decantation is most suitably em- ployed for heavy precipitates, which are not partly or wholly suspended in the liquid. It is accomplished by pouring off the liquid from the precipitate or by removing it by either syphon or pipette. By frequent addition of distilled water the precipi- tate is then washed out until the washings cease to show saline ingredients by chemical tests. Filtration is the separation of precipitates by means of an interposed septum. The septum for this purpose may either be pure sand as for strong acids, or asbestos, also muslin, or ab- sorbent cotton for non-corrosive liquids; but best of all and most generally employed for watery, alcoholic, etc. solutions is white, chemically pure, filtering paper, such as is known as “Swedish.” While plaited filters are employed in filtering solu- tions to clear them from suspended impurities, the plain filter only should be employed when the precipitate is to be used. For precipitates soluble in an excess of the solvent or partly or wholly suspended therein filtration alone is admissible, and the washing on the filter should be accomplished by means of a wash-bottle or spritz. The filter should be washed out on the funnel before adding the liquid holding the precipitate, and when this is to be done the pouring out should be guided by a glass rod. To remove precipitates from the filter the wash- ings should first be allowed to thoroughly strain off, and the filter should be placed on bibulous paper, with which gentle pressure is exerted until on examination the precipitate is found almost detached, and may be removed by a spatula to either a capsule, beaker, test-tube or watch-glass, as required. If the precipitate is to be dried, it may be placed with the filter in a dish or watch-glass, and this placed in a water bath or