﻿12 Prof. R, Bunsen on the Washing of Precipitates. 



X. 



In transferring the precipitate with 13 cub.l - 

 centiras. of water J 



For a single addition of water (26 cub. cen- 1 g 

 tims.) to run through J 



In draining the precipitate J^ 



Time required 14 



Weight of precipitate . . . 0*2439 grm. 

 Volume of wash-water . . 39 cub. centims. 

 Pressure 0*530 metre. 



In washing, by means of decantation, in the ordinary manner, 

 the amounts of chromium sesquioxide found were as follows :• — 



grm. 

 II. 0*2458, after 5 decantations, washed to the * part. 



III. 02452 „ 7 „ „ 2 -o^oo Part- 



IV. 0J2443 „ 10 „ „ , oooooooo P art - 



0-2451 mean. 



By the use of the pump : — 



grm. 



V. 0*2435, after 5 additions of water. 



VI. 0*2434 „ 4 



VII. 0*2432 „ 3 



VIII. 0*2435 „ 2 



IX. 0*2439 „ 1 addition of water. 



X. 0*2439 „ 1 



0*2436 mean. 



Hence the probable amount of chromium sesquioxide con- 

 tained in the solution, according to the experiments with the 

 pump, was 0*2436 grm.; according to the old method of decan- 

 tation it was somewhat higher, namely 0*2451 grm. This excess 

 of 1*5 milligramme shows that the adhesion of the soluble mat- 

 ters to the precipitate and to the filter is, in consequence of the 

 greater pressure, more easily overcome in the new method than 

 in the customary process ; it follows, therefore, that w T e can ob- 

 tain a more complete washing by the new method than by the 

 old. The old process of decantation required 108 minutes and 

 1050 cub. centims. of water to effect a washing to the 5^000 

 part; the new, on the contrary, only 12 to 14 minutes, and not 

 more than 39 to 41 cub. centims. of wash-water. If a precipitate 

 be heated in a platinum crucible immediately after filtration by 

 the older process, a portion will inevitably be projected out of 



