§ 39. FILTRATIOX. 37 



For fuller details in regard to this mode of filtration 

 we refer to the original articles. 



c. When several portions of a solvent, such as water, 

 alcohol, or ether, are to be made to act on a substance, 

 each portion can be readily separated from the substance 

 by the following contrivance. 



Close the flask with a rubber cork pierced with two 

 holes ; through one of these pass a short bent tube, like 

 the shorter tube of the common washing-bottle, and in 

 the other hole fit a tube which is widened out, funnel-like, 

 at one end, but not so much as to prevent its being put 

 into the flask easily ; near the other end, this tube is bent 

 at an acute angle, and the end is drawn out to a point 

 and left with a pretty large opening, after the fashion of 

 the other tube of the washing-bottle ; the long arm of 

 the tube should reach nearly to the bottom of the flask, 

 and have a piece of fine linen firmly bound over its mouth. 



The substance and the solvent having been digested in 

 the flask, when the solvent is supposed to be saturated, 

 and it is desired to replace it by a fresh quantity, force 

 air into the flask by the shorter tube and the solution will 

 be expelled, and at least partially filtered on its way 

 through the muslin ; then, if the end of the longer tube 

 is immersed in a fresh quantity of the solvent, this may 

 be drawn into the flask by suction at the mouth of the 

 short tube. 



If heat is used, the mouth of the short tube may be 

 connected with the Iquoer end of a Liebig's condenser ; 

 then the vapors of the solvent are condensed, and the 

 liquid flows back into the flask, and the ebullition can be 

 maintained as long as is desired without the necessity of 

 adding fresh quantities of the solvent to replace what is 

 lost by evaporation ; when it does become necessary to 

 replace this portion of the solvent by a fresh one, the rub- 

 ber tube that connects the flask with the condenser may 

 be closed with a clamp, and, the application of heat being 



