362 CAPILLARY ATTRACTION, ETC. [MEMOIR XXVI. 



sue, continually acting as a perpetual condensing engine, 

 brings the two media in contact with each other under 

 extremely different conditions the one in a compressed 

 state, but ready to exert the whole of its elastic force ; 

 the other in a state perhaps little varying from its nor- 

 mal condition. 



Moist membranes and films of water, by reason of 

 their affinity for gaseous substances and their 

 consequent condensing action, become the origin 

 of great mechanical power. I have seen car- 

 bonic acid pass into atmospheric air through 

 India-rubber against a pressure of ten atmos- 

 pheres, and sulphuretted hydrogen against a 

 pressure of twenty-five atmospheres. 



The apparatus with which these results were 

 obtained may be thus described. A strong 

 glass tube, a , Fig. 85, seven inches or more 

 in length and half an inch in diameter, is her- 

 metically closed at one end, through which a 

 pair of platinum wires, &, <?, pass to the interior, 

 parallel but not touching. The other end, a a, 

 has a lip or rim turned on it. Between the 

 platinum wires a gauge tube, d, is dropped. 

 On the top of the gauge tube a small test glass,/, is 

 placed, to contain a reagent suited to the gas under trial, 

 as lime-water for carbonic acid, acetate of lead for sul- 

 phuretted hydrogen, litmus water for sulphurous acid. 

 Sometimes, instead of this test tube, a piece of paper 

 soaked in the proper reagent was employed. The large 

 tube was then filled with water to the height e e, and 

 over its lip a thin sheet of India-rubber was tightly tied, 

 and over this again, to give strength, a very stout piece 

 of silk. Everything being thus arranged, the projecting 

 wires b y c, were connected with a voltaic battery ; decom- 

 position of the water ensued, oxygen and hydrogen be- 



