598 
NOTES AND ABSTRACTS IN CHEMISTRY AND PHARMACY. 
On opening the pinchcock a, water flows from the tube l into the enlarged 
glass vessel b, and thence down the leaden pipe c. This pipe has a diameter of 
about 8 millims. (£ in.), and extends downwards to a depth of 30 or 40 
feet, and ends in a sewer or other arrangement serving to convey the water 
away. The lower end of the tube d possesses a narrow opening; it is hermeti¬ 
cally sealed into the wider tube 5, and reaches nearly to the bottom of the 
latter. A manometer is attached to the upper continuation of this tube d by 
means of a side tube at d x ; at d 2 is attached a strong thick caoutchouc tube 
possessing an internal diameter of 5 millims. ( T % in.) and an external diameter 
of 12 millims. (| in.) ; this leads to the flask which is to be rendered vacuous, 
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 f, in which, when 
one washes a filter with hot water, the steam which may be carried over is con¬ 
densed. All the caoutchouc joinings are made with very thick tubing, the 
internal diameter of which amounts to about 5 millims. (-^in.), the external 
diameter to about 17 millims. (fin.). The entire arrangement is screwed down 
upon a board fastened to the wall, in such a manner that each separate piece of 
the apparatus is held by a single fastening only, in order to prevent the tubes 
being strained and broken by the possible warping of the board. On releasing 
the pinchcock a, water flows from the conduit l down the tube c to a depth of 
more than 80 feet, carrying with it the air which it sucks through the small 
opening of the tube d in the form of a continuous stream of bubbles. No ad¬ 
vantage is gained by increasing the rapidity of the flow, since the friction 
exerted by the water upon the sides of the leaden pipe acts directly as a counter¬ 
pressure, and a comparatively small increase in the rapidity of the flow is ac¬ 
companied by a great increase in the amount of this friction. Accordingly at 
(j is a second pinchcock, by which the stream can be once for all so regulated 
that, on completely opening the cock a, the friction, on account of the dimin¬ 
ished rate of flow, is rendered sufficiently small to allow of the maximum degree 
of rarefaction. Such an apparatus, when properly regulated once for all by 
means of the cock </, exhausts in a comparatively short time the largest vessels 
to within a pressure of mercury equal to the tension of aqueous vapour at the 
temperature possessed by the stream.* 
To employ this pump for rapid filtrations, it is necessary to devise such a sup¬ 
port for a paper filter that it shall support the atmospheric pressure without any 
risk of breaking. Prof. Bunsen has solved this problem in a very simple 
manner. 
An ordinary glass funnel has only to be so arranged that the filter can be 
completely adjusted to its sides even to the very apex of the cone. For this 
purpose a glass funnel is chosen possessing an angle of 60°, or as nearly 60° as 
possible, the walls of which must be completely free from inequalities of every 
description ; and into it is placed a second funnel made of exceedingly thin 
platinum-foil, and the sides of which possess exactly the same inclination as 
those of the glass funnel. An ordinary paper filter is then introduced into this 
compound funnel in the usual manner ; when carefully moistened and so ad¬ 
justed that no air-bubbles are visible between it and the glass, this filter, when 
filled with a liquid, will support the pressure of an extra atmosphere without 
ever breaking. 
The platinum funnel is easily made from thin platinum-foil in the following 
manner :—In the carefully chosen glass funnel is placed a perfectly accurately 
fitting filter made of writiug-paper; this is kept in position by dropping a little 
* The time required to obtain the above degree of exhaustion in a flask of from 1 to 3 litres 
capacity ranges from six to ten minutes; the quantity of water necessary amounts to about 
40 or 50 litres. 
