A treatise on materia medica, pharmacology, and therapeutics / by John V. Shoemaker ... and John Aulde.

  • John Veitch Shoemaker
Date:
1889-1891
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on materia medica, pharmacology, and therapeutics / by John V. Shoemaker ... and John Aulde. Source: Wellcome Collection.

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    ground into the form of powder, the hner portions being secured by the addition of water, and the coarser particles returned to be re-ground, and thus the process is repeated until the requisite degree of cominiim- tion is secured. LIXIVIATION is practiced in order to dissolve out a soluble salt from a compound or mixed solid by the use of water and subsequent evapora- tion of the solution. MACERATION is sometimes practiced as a preliminary to the i)repa- ration of infusions and decoctions, the liquid generally being alcohol, in which the comminuted substance is placed. The liquid used in macera- tion is called the menstruum; the insoluble matter remaining after ex- pression is called the marc. Maceration dilfers from digestion in that it requires a longer time for its completion, and the use of an alcoholic menstruum, as in the prepa- ration of tinctures, instead of water. PERCOLATION OR DISPLACEMENT are names applied to the method by which, through the agency of a suitable solvent, we obtain the soluble ingredients of a substance prepared in the form of powder, and is largely used in the preparation of tinctures. No little skill is required for conducting the process successfully, and much depends upon the character of the substance to be acted upon. This is generally in the form of a fine powder, but the degree of comminution must be regu- lated by the character of the drug. If too fine it becomes impermeable to the menstruum, and prevents its descent; if the powder is too coarse the spirit fails to saturate the particles, and the active properties are not recovered. To overcome this objection the pharmacopoeia directs the degree of fineness requisite for the more important tinctures by requir- ing the powder to be previously ])assed thi’ough sieves of definite dimen- sions. The process of percolation may be thus described : The substance, in the form of powder, which is to be subjected to the operation, is packed in a short, wide tube, closed at one end by tying a piece of mus- lin or flannel over it and pouring into the tube the menstruum ; as the liquid gradually filters its way through the column of powder, the solu- ble ingredients are dissolved and drop into the receiver below. In some instances it is better to first combine the menstruum with the powder before placing in the percolator. The mixed form of first macerating and then percolating is preferable to either process used alone. To pre- vent closure of the pores in the column of powder, a layer of pebbles or fine sand may be placed at the bottom of the tube. The vessel holdiuir the powdered drug is called the percolator; the liquid used as a solvent is the menstruum until it reaches the receiver, when it is termed the percolate. Minute instructions for percolation will be found in the pharmacopoeia.