30 § 38. AXALYTICAL MANIPULATIOX. 



occupy more than one-thirel or one-fourth the space taken 

 up by the liquid above it ; and, moreover, for convenience 

 in filtration, the beaker should not be more than two- 

 thirds or three-fourths filled by the mixture. 



A few i:)recipitates may be filtered out at once, in quan- 

 titative analysis, but in most cases digestion in a warm 

 place for a longer or shorter time, is required. The beak- 

 er should be carefully covered during the digestion, so 

 that no particle of dust can get in, and the operation is 

 most conveniently performed on the sand-bath. 



When about to transfer the contents of the beaker to 

 the filter, smear a very little tallow under the lip of the 

 former, wet a glass rod in the liquid, and hold tliis wet 

 rod against the lip of the beaker in such a manner that 

 the liquid will run down the rod and against one side of 

 the filter. 



Of course every particle of the precipitate must be 

 transferred to the filter if the two are to be weighed 

 together, with or without ignition. Most of the preci- 

 pitate can be rinsed out of the beaker by means of 

 the jet from the washing-bottle; if any particles re- 

 main adhering to the glass, they may be loosened with 

 a stiff feather ; or, when the precipitate is to be ignited 

 before being weighed, a quarter or a half of a filter, of 

 the same size and kind as that in the funnel, may 

 be moistened slightly and rubbed over the sides and bot- 

 tom of the beaker with the aid of the glass rod, or of 

 glass-pointed pincettes, and then transferred to the filter, 

 with most of the remainder of the precipitate adhering 

 to it ; a little subsequent rinsing with the Avash-bottle 

 will leave the beaker thoroughly cleansed ; or the precipi- 

 tate that adheres obstinately to the sides of the beaker 

 may be dissolved in very dilute acid, and re-precipitated 

 on neutralization of the acid with ammonia or soda, and 

 the addition of a little more of the precipitant. If the 

 second method of cleaning the beaker is followed, remem- 



