16 PHARMACY 



Expression. This is the process of separating a liquid from 

 a solid by pressure. It is especially used in pharmacy for the pur- 

 pose of separating a liquid from a drug residue (marc) left after 

 percolating or in separating fixed oils. The ordinary tincture or 

 fruit press may be taken as an example. 



eolation, or Straining. This is the process of separating solid, 

 coarse particles from a liquid by pouring through a cloth or strainer. 



Filtration. This is the process of separating fine or coarse, solid 

 particles from a liquid by pouring it through a finely porous material, 

 such as a filter paper. 



Decantation. This means simply carefully pouring off most of 

 the liquid portion, leaving the rest in the vessel. By repeating the 

 process several times and adding more solvent each time, practically 

 all the soluble material may be removed from the precipitate. 



Clarification. This is the process of rendering turbid materials 

 clear and transparent by removing the suspended solid bodies. 

 Often -when the solid particles cannot be removed by the filter, they 

 may be removed by agitating them with some insoluble powder, or 

 by adding egg albumen or shredded filter paper and by boiling or 

 by centrifuge. 



