R. Bunsen on the Washing of Precipitates. 327 
of a doubly perforated caoutchoue cork, through one of the 
holes of which the neck of the glass funnel is passed to a depth 
of from 5 to 8 centimeters (fig. 3); through the other is fitted 
@ harrow tube open at both ends, the lower end of which is 
brought exactly to the level of the lower surface of the cork, to 
the other is adapted the caoutchouc tube connected with the 
apparatus (fig. 4) destined to produce the requisite difference in 
pressure : this apparatus will be described immediately. The 
flasks are placed in a metallic or porcelain vessel (fig. 3), in 
the conical contraction of which several strips of cloth are 
fastened. This method of supporting the flask has the advan- 
tage that, in one and the same vessel, flasks varying in size 
from 0-5 to 2°5 liters stand equally well, and that, by simply 
laying a cloth over the mouth of the vessel, the consequences 
of an explosion (which through inexperience or carelessness is 
possible) are rendered harmless. 
_ It is impossible to employ any of the air-pumps at present 
im use to create the difference in pressure, since the filtrate not 
unfrequently contains chlorine, sulphurous acid, hydric sul- 
phid, and other substances which would act injuriously upon 
the metallic portions of these instruménts. I therefore employ 
Pp “oes 
the pinchcock a, water flows from the tube 7 into the enlarged 
18 attached a strong thick caoutchouc tube possessing an in- 
: millims. and an external diameter of 12 
millims.; this leads to the flask which is to be rendered vacu- 
ous, and is connected with it by means of the short narrowed 
tube k. Between the air-pump and the flask is placed the 
small thick glass vessel /, in which, when one washes with hot 
Water, the steam which may be carried over is condensed. All 
-€ caoutchouc joinings are made with very thick tubing, the 
internal diameter of which amounts to about 5 millims., the 
€xternal diameter to about 17 millims. The entire arrange- 
Ment is screwed down upon a board fastened to the wall, in 
