POWDERS PULVEBES 731 



POWDERS-PULVBRES 



Many medicines may be reduced to a rough powder in a 

 hand-mill such as that used for grinding coffee or pepper ; 

 or in an iron mortar (which should be fixed into a block of 

 wood), with a large, heavy, iron pestle, which ought to be 

 suspended from one end of a flexible rod running along the 

 ceiling, and fixed into the opposite wall. Preparatory to 

 further reduction, many roots and barks are pounded or 

 cut. To effect minuter subdivision, small quantities of the 

 coarse powders are reduced in hand mortars, of marble, or 

 Wedgwood ware, the latter being cheap, easily cleaned, and 

 little affected by acids. When a fine state of division is 

 required, the powder is put through wire-gauze or horse- 

 hair sieves, the meshes of which are made of suitable close- 

 ness. For light, pungent, or irritant powders, compound 

 sieves, closed in above and below, are used. To facilitate 

 reduction of tough vegetable drugs such as opium, they 

 are sometimes mixed with a hard salt, such as potassium 

 sulphate. To avoid tedious trituration, powders, like 

 calomel and flowers of sulphur, are conveniently obtained 

 by sublimation ; others, like magnesium carbonate or mer- 

 cury red oxide, by precipitation ; other insoluble substances, 

 like prepared chalk, by stirring in water, allowing the coarser 

 particles to settle, and pouring off the solution from which 

 the finely-divided powder is gradually deposited and dried. 

 Nauseous, deliquescent, efflorescent, and volatile substances, 

 and those given in large doses, cannot be conveniently 

 administered in powder. Active drugs are prescribed with 

 such inert substances as starch, gum, liquorice, or sugar 

 of milk. Powders, when not too bulky, are occasionally 

 dropped upon the patient's tongue, or introduced into the 

 mouth or nostrils by insufflation. When free of disagree- 

 able flavour, they are sometimes scattered upon or mixed 

 with the food. 



RESINS 



Resins are amorphous solids consisting of acids formed 

 from the oxidation of terpenes (C 10 H 16 ). They are insoluble 



