48 VOLTAIC BATTERIES MAY BE USED FOR PRODUCING GREAT PRESSURES. 



the barometer at 29-88, atmospheric air, under a pressure of two atmospheres and a 

 half, was exposed, under a sheet of India-rubber, to sulphurous acid gas, care being taken 

 that the temperature of the mercurial trough, and all parts of the arrangement, should 

 be as above. The passage of the gas took place with great promptness, the litmus 

 water, used to detect its presence, reddening rapidly. Now sulphurous acid, according 

 to the experiments of Dr. Faraday, condenses into a liquid at 45 F., under a pressure 

 of thirty inches of mercury ; we know, therefore, that in this trial the gas must have 

 existed in a liquid condition in the barrier, and yet it passed through into atmospheric 

 air, under a resistance almost two and a quarter times sufficient to condense it, and at 

 a temperature eight degrees lower. 



355. Having, progressed thus far in this part of the inquiry on the action of tissues, 

 it became important to find if any pressure which could conveniently be brought into 

 action would restrain the passage of gaseous matter. Resort was first had to the usual 

 mechanical condensing apparatus ; but they were found to be ill adapted to the purpose 

 in hand. The necessary motions were always productive of inconvenience, and it was 

 not found possible to carry the condensation to the degree required, or to avoid leak- 

 age from some of the numerous joints. After some trouble, the following contrivance 

 was fallen upon, which answers the end perfectly, is not open to the serious objections 

 of the former, and, requiring no cock or valve, can be readily made without leakage. A 

 tube of glass about one third of an inch in bore, of stout substance, and about ten inches 

 long, is bent into a kind of siphon, so that one leg shall be about six, and the other 

 two inches long. The extremity, a a, fig. 19, has a lip or rim turned round it at the 

 lamp ; while in the longer leg, a thin glass tube, c c, about one eighth of an inch in 

 bore, and closed at one end, is included to serve, as will be hereafter shown, as a gauge. 

 Next, the extremity, b, of the siphon is closed, there being inserted through it two pla- 

 tinum wires, d d, e e, parallel to each other, but not touching. The arrangement is then 

 ready for use. Suppose, for example, it was required to pass through India-rubber 

 sulphurous acid gas into atmospheric air, condensed by a pressure of five or six atmo- 

 spheres ; the long leg of the siphon is to be filled with water, which is excluded from 

 the gauge-tube c c, owing to the narrowness of its bore ; next, a strong decoction of lit- 

 mus is to be poured into the short leg until it is about half filled. The rim round the 

 extremity, a a, is then daubed with a piece of burning caoutchouc, and upon it is tied 

 a thin piece of that substance, with a fine but strong waxed thread. Over this is tied 

 a piece of stout silk or cotton cloth, for the purpose of fortifying the barrier ; the wires, 

 d d, e e, are then made to communicate with the poles of an active voltaic battery, and 

 the condensation commences; for the gas which is evolved from these electrodes rising 

 to the top of the tube, accumulates there, causing the column of water in the short leg to 

 rise and condense the atmospheric air above it. The membrane, though fortified, gives 

 way to a certain extent, becoming convex outward ; and as the accumulation of gas in 

 the long leg continues, the condensation of that in the short leg increases, as is indica- 

 ted by the gauge c c. A very thin India-rubber, of the diameter here used, will stand a 

 pressure of from six to twenty atmospheres without rupture, if its silk support is good ; 

 and I have found that anointing the edges of the rim with the burned substance enables 



