Constitution of the Atmosphere. 



243 



increases in quantity. But if any one will throw into a soap- 

 bubble one hundred measures of carbonic acid, and expose it 

 to atmospheric air, he will perceive a very different result to 

 that just mentioned, for instead of gas accumulating within 

 the bubble, a very extraordinary and rapid diminution will 

 ensue: this phaenomenon is not a little remarkable; it does not 

 require any instrumental arrangement to detect it. A bubble 

 of carbonic acid gas an inch in diameter, collapses in the 

 space of a few minutes to the size of a common pea. 



Again, if carbonic acid, &c. and atmospheric air are kept 

 from directly mingling with each other, by being separated by 

 a thin lamina of India-rubber, they will pass through the 

 barrier to intermix. Do they intermix with a force greater 

 than the pressure of one atmosphere ? Dr. Mitchell of Phila- 

 delphia found that carbonic acid would pass through a piece 

 of India-rubber, and diffuse itself into atmospheric air, though 

 resisted by a pressure greater than two atmospheres (63 inches 

 of mercury). This first cast doubts on the hypothesis of 

 gaseous action, for if it can be proved that these mixtures 

 are effected with a force greater than that which is measured 

 by one atmosphere, the idea that gases act towards each other 

 as vacua, necessarily falls to the ground. 



Allow me. Sir, to point out some experiments which seem 

 to bear on this matter. Let us examine, for instance, whether 

 sulphurous acid will pass into atmospheric 

 air with a force greater than the pressure 

 of one atmosphere. A tube of glass, about 

 one third of an inch in bore, and 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, has 

 a lip or rim turned on it, at the lamp; and 

 in the longer leg a thin glass tube cc, about 

 one eighth of an inch in bore, and closed at 

 one extremity, is included to serve, as will 

 be hereafter shown, as a gauge. Next, the 

 extremity h of the siphon is closed, there 

 being inserted through it two platinum 

 wires dd, e e, parallel to each other, but 

 not touching. The arrangement is thus 

 completed for use. Let us suppose it is re- 

 quired to pass through India-rubber, sul- 

 phurous acid gas, into atmospheric air 

 condensed by a pressure of five or six atmospheres; the long leg 

 of the siphon is to be filled with water, which is excluded from 

 the gauge tube c c, owing to its narrowness ; next, a strong de- 

 coction of litmus is to be placed in the short legi until it is half 



R 2 



c 



\JJ 



