PREPARATION OF PURE COMPOUNDS 



III. SEPARATION OF SOLID AND LIQUID. 

 FILTRATION. 



The mixture of solid and liquid may consist of suspended particles 

 consisting of residues of filter paper, etc., which do not require ex- 

 amination, or it may consist of matter requiring examination, obtained 

 either naturally or by evaporation of the liquid, or it may consist ot 

 solid in a crystalline form purified by crystallisation. 



Obviously the procedure to adopt is filtration. Filtration is effected 

 in several ways depending on the material. 



(a) Fluted or Pleated Filter Paper. 



Suspended matter is removed by filtration through a filter paper 

 folded in the ordinary way to fit a funnel, or better and more rapidly 

 through a fluted or pleated filter paper which exposes as large a sur- 

 face as possible to the liquid. A filter 

 paper is folded into quarters in the ordin- 

 ary way. Each quarter is then bisected 

 by folding towards the hollow of the 

 central fold, and each of these divisions 

 is bisected again in such a way that the 

 hollows and ridges alternate (Fig. 10). 

 More pleats are obtained in the same way 

 by bisecting the divisions and folding 

 alternately. The paper is thoroughly 

 pressed to make the pleats permanent. 



Such a filter paper is used for rapidly 

 filtering off a small number of particles 

 and also for filtering off solid matter which 

 is not crystalline, such as the residues re- 

 maining after extracting animal and plant 



tissues with solvents, residues which are not easily filtered by the 

 other methods. 



(b) Filter Plate. Buchner Funnel. 



The filtration of crystalline compounds is best effected by means 

 of a perforated porcelain plate placed in a funnel or a complete 

 funnel of porcelain of this pattern (Buchner or Hirsch funnel). The 

 perforations are covered over with a filter paper of the right size and to 

 prevent breaking of the paper two thicknesses may be used, or better 

 hardened filter paper. The paper is wetted with the liquid and sucked 

 down by a vacuum produced by a filter pump (Fig. 1 1). 



The substance is placed upon the paper and the liquid drained off as 



