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.

    29/856 (page 17)
    these metals is effected by pouring the fused mass in a thin stream from a height, into a large body of cold water. When a large quantity of a substance is partially reduced to powder, two means are adopted for separating the coarser particles, if it be a vegetable substance, the process of sifting through hair, \m’e, or gauze sieves, which are numbered according to the close- ness of the meshes, is resorted to. But wheu the substance is a mineral and insoluble in water, the simple process of elutriation {duo or elutrio, to wash out) is conveniently adopted. This is exemplified in the preparation of Creta prseparata and the non- officinal Calamina preeparata. It consists in stirring the powder ivith water, and after the subsidence of the larger particles, poiu’ing oft' the milky or turbid ftuid containing the finest, and then allow- ing these to subside, when the water is poured off, the sediment di’ained, and lastly dried. 2. The Separation op Fluids and Solids.—This may be effected, as just mentioned, by deposition {depono, to put down) ot the solid, and decantation {decanto, to pour off gently) of the fluid. The latter process may be eft’ected by simply pouring off the fluid if the deposit be heavy, but if not it is best to use a syphon, the immersed end of which should be gradually lowered as the liquid flows away, for if it be brought too near the deposit the suction action causes a rise in the latter. To prevent this, the end of the syphon should be closed, and an aperture or two made in the sides so as to induce a lateral, instead of an upward current. This process is illustrated in the preparation of Bis- muthi subnitras, Ferri carbonas sac- charata, &c. But the commonest pro- cess for the separation of solids and flmds is the filter (F.filtre, a strainer). Filtration (figs. 4,5), unless otherwise directed, is effected by means of white bibulous paper, sufficiently strong to support the weight of the fluid, and of close texture so as to prevent the passage of fine particles, and com- posed of pure cellulose. When the deposit is very finely divided (as, for example, precipitated chloride ot Sliver), the filter should be wetted before the mixture is placed in it, in order to decrease the size of the pores. Fig. 5 shows the mode of washing a precipitate. The stream of water should be directed around the margin of the paper. Calico filters are often employed when the object is the washing and preservation of the eposit, because the filtration can be more readily effected than with paper, and the water can be removed by wringing. Powdered glass t -g. or Liquor potassie), sand, and powdered charcoal {e.g., for B Fig. 4.