54 POWDERED VEGETABLE DRUGS 



conditions for powdering crude drugs should be as uniform as possible, 

 especially as to manner of grinding, of sifting, as to temperature and 

 dryness during grinding. Drying should be done at a constant 

 moderate temperature (60 degrees C.) in order to prevent the loss 

 of active constituents by heat. Gas ovens with thermo-regulators 

 are most suitable. 



3. Powdering. 1 For purposes of reducing vegetable drugs, various 

 drug mills are used, in some instances a mortar and pestle are sufficient. 

 Whatever the apparatus employed, it should have the desired opera- 

 tive effectiveness, irrespective of size and working capacity. The 

 larger, more carefully constructed mills, however, yield the most 

 uniform powders. It is practically impossible to prepare a uniform 

 powder by means of pestle and mortar, although this apparatus is 

 highly recommended by some authorities. It is a tedious process, and 

 the more delicate tissues are reduced to a fine powder long before the 

 more fibrous portions begin to be broken up; it is very difficult to 

 reduce bast, tracheids, vessels and similar tissues to anything like a 

 uniformly fine powder. Some authorities suggest that this difficulty 

 may be overcome by separating powders thus prepared into three 

 grades as to fineness, and in percolating to place the finest powder at 

 the bottom of the percolator. This suggestion is, however, not 

 practicable. 



4. Sifting. The fineness is determined and measured by passing 

 the powders through a sieve with meshes of known dimensions. These 

 meshes should be uniform and square and their dimensions should 

 indicate the size of the opening, irrespective of the diameter of the 

 wire, silk, hair or other substance employed in sieve construction. 

 Here, again, it is found that the larger machine-operated sieves are 

 more satisfactory than the smaller hand-sieves. Sifting should be 

 done carefully. It is necessary to clean the sieves frequently, as 

 very fine particles cling to the wire, silk or hair, especially at the angles, 

 thus allowing only particles to pass through which are considerably 

 smaller than the free mesh. 



The fineness of powders is' indicated by the diameter of the meshes 

 given in the metric system or English system, representing a definite 

 number of meshes to the centimeter or to the inch. 



The homogeneity and fineness of the powder is greatly modified 

 by the force with which the sieve is operated. Sifting lightly allows 

 only the finer particles to pass through; upon shaking the sieve with 

 greater force coarser particles pass through also. Sieves should be 



1 For description of apparatus and methods for powdering, sifting, etc., of 

 vegetable drugs, consult a standard American work on the Practice of Pharmacy. 



