CHEMISTRY. | 3) 
The latter, however, contains a part of the liquid, as also of the substance 
causing the precipitation, both of which must be removed. This can, in 
most cases, only be done by long continued washing in distilled water. An 
arrangement is therefore needed which shall allow an uninterrupted current 
of pure water to flow on the precipitate, so as to wash entirely away from it 
anything soluble in water. For this purpose, we make use of the two- 
branched tube (pl. 31, fig. 47), which is inserted into the cork of a bottle 
filled with water, as seen in fig. 48, B. The tube (fig. 47) is immersed up 
to about ab in the liquid in the funnel, A (fig. 50). The two slides, d, d, 
can be fixed on the vertical rod, D, at any height, so that the washing bottle, 
B, may have any appropriate position. When the level of the liquid in the 
funnel A has sunk so far that the tube (fig. 47) is immersed only to cd, the 
column of water, abcd, higher by ac or bd, has a tendency to settle at 
a height equal to that of the liquid in the funnel A, the atmosphere pressing 
on the column through the tube e. It therefore flies out, and in the space 
thus reached there enters a bubble of air through the tube e. Now as air is 
much lighter than water, this bubble immediately ascends into the tube, f, 
filled with water, and enters into B (figs. 48, 49, and 50). By this the 
water in the funnel A again rises to the height ab, this action being 
continued uninterruptedly. When, however, the water level in the funnel 
is the same with that within the tube ab, the action of the tube (fig. 47) 
ceases spontaneously ; for as soon as the column adcd no longer flows out, 
the remaining column in the tube f is supported by the pressure of the 
atmosphere acting through the tube e, like the mercury of a barometer. 
The adhesion of the water to the conical part of the tube likewise facilitates 
the action of the tube, so that the column abcd stands generally a little 
higher than the surface of the water in the funnel A. This two-legged 
tube may easily be replaced by two tubes set close together in a cork, the 
action being the same in both arrangements. An arrangement of this kind 
is intelligible from an examination of jig. 49. 
A simple filtering apparatus is shown by figs. 51 and 52. A represents 
the stand, B a tumbler into which the liquid is filtered, C the funnel, D 
differently arranged slides, which, by means of screws, can be fixed at any 
elevation on the vertical rod of the stand A. 
In washing the precipitate, instead of the double-legged tube of the 
preceding apparatus, we may make use of the washing bottle, as shown in 
pl. 30, fig. 49, and pl. 31, fig. 54. In the first of these we blow into the 
bottle, half full of water, thereby compressing the contained air. On 
quickly inverting the bottle the pressure of the air forces out the water in a 
fine stream from the pointed glass tube which had been inserted into the 
aperture of the bottle by means of a cork. The water escapes, therefore, 
in a jet, and by directing this upon the filter the precipitate is quickly 
stirred up and well washed. The second apparatus (fig. 54) serves the 
same purpose, only the air is blown in through the tube b, and the water 
driven out through the tube a, which reaches nearly to the bottom of the 
bottle half full of water. 
Funnels (pl. 80, fig. 46). The filtering funnels used in chemical 
ICONOGRAPHIC ENCYCLOP2DIA.—VOL. I. 30 465 
