SIR B. C. BRODIE ON THE ACTION OF ELECTRICITY ON GASES. 
439 
action, which may be done by placing fragments of ice in the interior of the tube, and 
also in the water contained in the external cylinder in which the induction-tube is 
immersed. If a lower temperature still be desired, the ice may be replaced by a 
mixture of ice and salt ; in this latter case the precaution of tilling the interior tube 
also with the saline solution must not be omitted. When the tube is thus cooled, 
either with ice or with ice and salt, the external cylinder containing the refrigerating- 
mixture should be wrapped in thick flannel. The temperature can readily be thus kept 
during a long experiment of six or eight hours’ duration at 0° C., or even at — 10° C. 
The electrized gas is collected and preserved for the purpose of experiment in a gas- 
holder, delineated in Plate LI. fig. 4. On this side of the induction-tube connexions of 
caoutchouc can no longer be employed, this substance being instantaneously corroded 
by even the minutest trace of ozone, and the junction between the gas-holder and the 
induction-tube is effected by means of what may be termed a paraffine-joint. Over the 
tubes to be connected, which are placed close together, is slipped a piece of glass tube 
into which they exactly fit, and from which they are separated by a capillary space ; a 
fragment of pure paraffine is placed at the external junction of the tubes ; the union 
of the tubes is effected by gently melting the paraffine ; the liquid paraffine is extremely 
limpid, and runs into and fills up the narrow space between the tubes. When the 
paraffine is solidified, the tubes are united by a joint, which is perfectly air-tight, 
which will resist very considerable pressure, and which is quite unaffected by the 
passage of the ozone. This simple joint is an essential feature of this arrangement, and 
would doubtless be of great service in many forms of gas-apparatus. 
The gas-holder consists of a glass bell (p) contained in a glass cylinder (<y), in which it 
is suspended, being supported by a knob of glass passing through a wooden cap fitted 
to the top of the jar ; this cap is made in two pieces, which are subsequently united so 
as to be readily placed in a proper position as a support to the glass bell. The wooden 
cap was coated internally with paraffine, to protect it from the effects of accidental contact 
with the acid. It would, however, be far better to make the cap of glass, which could 
easily be done. 
At a superior level is placed a glass jar ( r ) containing pure and concentrated sulphuric 
acid ; this jar is connected by a siphon-tube, s (in which is placed a glass stopcock), with 
the lower cylinder, q. This upper jar, which I shall term the reservoir, is closed by a 
wooden cap, t , which also would be better made of glass, through which the siphon-tube 
passes, and in which is also fitted a second glass tube, u. The gas from the induction- 
tube is delivered at n, whence it passes into the gas-holder by an arrangement of tubes, 
which is best understood from the drawing. 
I will now describe the way in which the apparatus is worked. A quantity of con- 
centrated sulphuric acid, just sufficient to fill the glass bell (p) and the external cylinder 
(q) to the top of the bell, is placed in the reservoir r, the siphon-tube being filled with 
the same. The stopcock at v is closed, and the stopcock w open ; the glass stopcock in 
the siphon-tube ( s ) is now opened, the air is expelled from the glass bell (p), which is 
