FORCE OF PASSAGE THROUGH MEMBRANES. 



155 



lapse lias occurred. If the law of diffusion here held good, the bubble 

 should rapidly distend. 



Moist membranes and films of water, by reason of their chemical affin- 

 ity for gaseous substances, and their consequent condensing Condensingac . 

 action, become the origin of great mechanical power. Under tion of mem- 

 such conditions, I have seen carbonic acid pass into atmos- 

 pheric air, driven, as it were, by the ; action of the membrane against a 

 pressure of ten atmospheres, and sulphureted hydrogen against a pres- 

 sure of twenty-five atmospheres, and, even against these great resistances, 

 the passage is accomplished with so much promptness as to lead to the 

 inference that a membrane will cause one gas to diffuse into another, even 

 though the apparent resistance be indefinitely great. 

 mg. 7i. In Fig. 71 is given a representation of the arrangement by 

 which these results were obtained. It consists of a strong 

 glass tube, seven inches or more in length and half an inch in 

 diameter, hermetically closed at one end, through which a pair 

 of platina wires, , <?, pass into the interior of the tube parallel 

 but not touching. The other end, a a, has a lip or rim turned 

 on it. Between the platina wires, a gauge-tube, d, is dropped, 

 to show the amount of condensation. On the top of the gauge- 

 tube a small test-tube, f, is placed, to contain a reagent suited 

 to the gas under trial, as lime-water for carbonic acid, acetate 

 of lead for sulphureted hydrogen, litmus-water for sulphurous 

 acid. Sometimes, instead of this test-tube, a piece of paper, 

 soaked in the proper reagent, was employed. The Measure of the 

 large tube was then filled with water to the height force of infii- 

 e e. Its lip or rim, a a, being next smeared with 

 burnt India-rubber, to insure absolute freedom from leakage, 

 a thin sheet of India-rubber was tied tightly over it, and over 



Great force of . ' . J . 



infiltration, this again, to give strength, a very stout piece of silk. Every 

 thing being thus arranged, the projecting wires, , c, were connected with 

 a voltaic pile, decomposition of the water ensued, oxygen and hydrogen 

 being disengaged, and a condensed mixture of atmospheric air and those 

 gases accumulated in the space a a e e, the gauge-tube showing the ex- 

 tent to which the condensation had gone. Now if the little tube, f, had 

 been filled previously with lime-water, and the whole arrangement was 

 introduced into, a jar of carbonic acid gas, the upper part of the lime- 

 water presently became milky, and after a time a copious precipitate of 

 carbonate of lime subsided. This would readily take place when the 

 gauge was indicating a pressure of ten atmospheres. In like manner, 

 when a piece of paper imbued with carbonate of lead had been introduced 

 into the tube, and a pressure of 24| atmospheres accumulated, on intro- 

 ducing the instrument into a vessel of sulphureted hydrogen, the paper 



