SIE B. C. BEODIE ON THE ACTION OF ELECTEICITY ON OASES. 
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mark b ; the capacity of the pipette having been determined between these points, a 
definite volume of gas at a known temperature and pressure was thus delivered at the 
exit-tube i. Evidence of the extreme accuracy of this method of measurement will 
shortly be given. It is, so far as I am aware, the first application to the estimation of 
the volume of gases of those principles of pipette-measurement which have been of 
such good service to the chemist in the case of the measurement of liquids. 
In order to estimate the changes in bulk which the electrized gas underwent in the 
various experiments hereafter described, the measuring-apparatus was employed of which 
a drawing is given in Plate LII. fig. 6. In this apparatus, which I shall term the aspirator, 
the volume of gas at 0° C. and 760 millims. pressure is ascertained by determining the 
pressure which it is necessary to put upon the gas in order to cause it to occupy a known 
space at a known temperature. This is the principle of Kegnault’s apparatus for gas- 
analysis, and also of Frankland’s apparatus. 
The apparatus consists of a cylinder of strong glass (a), connected by an iron tube with 
an iron reservoir (b). containing an amount of mercury rather more than sufficient to fill 
the cylinder a. In the iron tube connecting the cylinder and the reservoir is inter- 
calated a stopcock (c), by which the connexion between the cylinder and reservoir may 
at pleasure be made or cut off. In the reservoir b a small iron tube ( d ) is inserted, con- 
nected by a tube of caoutchouc with a forcing-pump firmly fixed to the table on which 
the apparatus is placed. By means of this forcing-pump the air contained in the upper 
part of the reservoir may be compressed, and any required pressure put upon the mercury 
contained in it. The cylinder a is cemented, by means of a resinous cement, into two steel 
caps (e and/’); the lower cap (f) is screwed firmly upon the support of the apparatus, 
which is made of iron. The cylinder is connected, by means of a channel cut in the 
lower part of the steel cap (f) and continued through the iron frame, with a glass tube (7/), 
which is about half an inch in diameter and graduated in millimetres : this tube I shall 
speak of as the pressure-tube. The cylinder a and the pressure-tube g are thus in per- 
manent connexion, and constitute one vessel, which is broken into parts solely for facility 
of construction. This apparatus is supported upon three screws, as shown in the figure, 
by the adjustment of which the pressure-tube g is placed in a perpendicular position 
before the commencement of the experiment. A piece of strong glass tubing, of fine 
bore, is cemented into a steel socket which forms part of the steel cap e, the upper end 
of the same glass tube being similarly cemented into a steel socket (A), on the upper 
part of which a screw is cut by which it is connected with a steel stopcock (k). Two 
steel sockets, similar to the socket h, are screwed into the stopcock (k) and two glass 
tubes ( l and m) are cemented into these sockets; the steel stopcock k is what is termed 
a three-way stopcock, in which the channels are so cut that a communication may be 
made between the tube l and the cylinder a, or between the tube m and the cylinder a , 
or between the tubes l and m (all other communications being shut off), at pleasure, or 
the communications may be entirely closed. 
In the cylinder a is placed a thin piece of glass rod, to which seven points are 
