324 ft. Bunsen on the Washing of Precipitates. 
tional to the difference in pressure : this is clearly shown by the 
following experiments, made with pure water and a. filter con- 
sisting of a thin plate of artificial pumice-stone. The thin 
plate of pumice was hermetically fastened into a funnel consist- 
ing of a graduated cylindrical glass vessel, the lower end of 
which was connected with a large thick flask by means of a 
tightly fitting caoutchouc cork. The pressure in the flask was 
then reduced by rarefying the air by means of a method .to be 
described upon another occasion ; and for each difference of 
pressure p, measured by a mercury column, the number of sec- 
onds ¢ was observed which a given quantity of water occupied in 
passing through the filter. The following are the results :— 
i, 
t. pt. 
0°179 91°7 16°4 
0-190 81:0 15°4 
0°282 52°9 14°9 
: 0°472 33°0 15°6 
In the ordinary process of filtration, » on the average 
amounts to no more than 0° to 0:008 meter. The advan- 
times, or, say, to an entire atmosphere, without running any 
risk of breaking the filter. The solution of this problem 1s 
hat the filter can be completely adjusted to its sides even 10 
the very apex of the cone, For this purpose a glass funnel 18 
portied seman 2 an angle of 60°, or as nearly 60° as possible, 
the walls of which must be completely free from inequalities ° 
ordinary | 
- funnel in the usual manner ; when carefully moistened and 50 
pressure of an extra atmosphere without ever breaking. 
The platinum funnel ig els made from thin platinum-foil 
in the following manner:—In the carefully chosen glass funnel 
