14 Operations used in Quantitative Analysis [14, 15 



14. Occasionally other liquids besides water are necessary 

 for washing certain precipitates ; for instance, ammonium 

 phospho-molybdate must be washed with dilute nitric acid, 

 and ammonium magnesium phosphate must be washed with 

 dilute ammonia. In all cases where the washing liquid gives 

 off objectionable fumes a special form of ivash bottle is neces- 

 sary. The stopper is drilled with three holes (see fig. 14) 

 which contain respectively a short tube ter- 

 minating both just inside and just outside the 

 stopper (a, fig. 14), an ordinary tube with a 

 jet (£, fig. 14), and a blowing tube with a trap 

 to prevent the fumes from passing back into 

 the mouth (c, fig. 14). This trap is very simple 

 in its structure, consisting merely of a piece of 

 fig. i 4 .— Ammonia india-rubber tubing stopped up at one end by 

 a piece of glass rod, and having a longitudinal 

 slit about half-an-inch long cut in one side of it. In using 

 this wash bottle the operator must keep his finger on the tube 

 a whilst blowing, and remove it when he wants the spray to 

 cease, otherwise it will continue to run for some little time 

 after the blowing has been stopped. 



THE FILTER PUMP 



15. In laboratories where a good pressure of water is 

 obtainable filtration may be greatly accelerated by the use of 

 the filter pump. A very convenient form of apparatus is 

 shown in fig. 15. a is a Geissler's filter pump; b is a bottle 

 with a good cork doubly pierced ; and c is a stout flask 

 having a tube sealed in one side of its neck. By means of 

 the pump a partial vacuum is caused in c, so that the pressure 

 of the air outside forces the liquid through the filter into the 



