PHARMACEUTICAL PROCESSES 73 



Levigation. — Somewhat similar to trituration, but per- 

 formed with a slab and mvller. These should be made of 

 glass, or some non-absorbent material. 



Elutriation. — This consists in mixing the powder, ob- 

 tained by some of the former comminuting processes, with 

 water ; agitating it ; allowing the coarser particles to settle, 

 and pouring off the supernatant liquid which holds the finer 

 particles in suspension. The powder settles from the latter 

 and is dried. 



MECHANICAL PROCESSES. 



Processes by which liquids are separated from solids, 

 and by which active principles and soluble constituents are 

 separated from the inert portion of the drug. 



Decantation. — The process by which solids are allowed 

 to subside in a mixture and the supernatant liquid is slowly 

 poured off or decanted. Liquids which will not mix, or that 

 are of different Sp. Gr., may be decanted one from the other. 



Filtration. — This is the process of separating a solid 

 insoluble substance from a liquid by passing the liquid 

 containing it through a porous substance called &filter. The 

 filter commonly used consists of unsized or bibulous paper, 

 although cotton, muslin, felt, earthenware, and other sub- 

 stances are employed. 



Percolation consists in ,the following process : A pul- 

 verized vegetable drug (containing both soluble and in- 

 soluble constituents) is placed in a conical vessel, or per- 

 colator, and subjected to the action of a liquid called a 

 menstruum, when the soluble portion, or percolate, flows 

 from the lower opening.- The menstruum as it descends 

 becomes more and more saturated with the soluble con- 

 stituents of the drug. The first that escapes is the strong- 

 est, and each successive portion of the percolate becomes 

 weaker until the drug is exhausted. The percolate should 

 not drop faster than one or two drops a second. Percolation 

 is employed in making tinctures, fluid and solid extracts, 

 syrups and some other fluid pharmaceutical preparations. 



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