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.

    81/656 (page 77)
    PERCOLATION. Percolation or Displacement is one of the most impor^ tant processes in Pharmacy, being extensively used in the prepara- tion of tinctures. It consists in packing into a short wide tube, closed at one end by tying a piece of calico over it, the substance, in a state of coarse powder, whose virtues are desired to be extracted, and pouring into the tube the men- struum—generally proof spirit. As the spirit filters its way through the column of powder it dissolves out the soluble parts, and drops finally into the receiver below as a bright tincture. The process may thus be defined to be '-'the filtration of a liquid through a porous column of a powdered material, so that it may extract its soluble matter. It is not adapted to gummy or ad- hesive substances, but possesses the great advantages over maceration in being quicker, and in the fact that after the fluid has ceased to drop, the tincture still left in the tube can be displaced by pouring in more spirit or water on the top of the marc. The mixed form of first macerating and then percolating, which is generally directed for the manufacture of tinctures, is decidedly better than either process used sepa- rately. At the bottom of the tube, immediately over the calico, a layer of fine pebbles or coarse river sand prevents the powder closing its pores. [Fig. 21 represents the most suitable form of apparatus.] Great skill is required in carrying out the process of perco- lation, and much depends upon the degree of comminution which the substance receives. If the powder be too fine, it gets into a cake, and prevents the passage of the spirit; and if too coarse, the spirit runs between the particles without dissolving out their active properties, flowing in little channels through the tube into the receiver. The Pharmacopoeia now states the degree of fineness requisite for several vegetable tinctures, by ordering the powder to be passed through sieves of definite make. A good deal, also, depends upon the way in which the powder is packed into the tube, and experience only Fig. 21.