16] 



The Filter Pump 



15 



flask. In using the filter pump the following precautions must 

 be taken : 



(a) Place a small platinum cone at the bottom of the 

 funnel to prevent the breaking of the filter paper. 



{b) See that the paper fits exactly into the funnel. 



(c) Turn on the water in the pump very gradually. 



(d) Never allow the filter to become quite empty. 



DRYING PRECIPITATES 



16. The method of drying depends on the treatment which 

 is to follow. If, as is most usual, the filter paper is to be 

 burned and the precipitate ignited and weighed, then the 

 drying may be carried on rapidly in an air oven. A very con- 

 venient filter drier is easily made from an old biscuit tin. A 

 line is drawn round the tin four inches from the top. Sixteen 

 holes, four on each side, are made in the tin along this line. 

 A piece of No. 16 B.W.G. copper wire is threaded backwards 

 and forwards through these holes, so as to form a network 

 inside the tin, with meshes parallel to its sides. The tin may 

 now be placed on a large tripod in such a manner that the 

 network of wires is in a horizontal plane. The funnel, covered 

 with a piece of filter paper, is placed upright in one of the 



