PERCOLATION* THROUGH EXCESSIVELY THIN FILMS OF WATER, AS SOAP BUBBLES. 21 



edge of the upper glass through the water in the saucer ; the cock is next closed, and 

 the apparatus placed on the trough shelf as long as the operator desires the experiment 

 to continue. Keeping that position when the cock is once more open, the gas passes 

 into the lower glass until the bubble is entirely collapsed, when the cock is again closed, 

 the contents of the bubble being now ready for measurement or analysis. As the gas 

 passes from the bubble into the lower jar, the water rises from the tin saucer into the 

 cupping-glass above, confining the gas that was outside of the bubble ; this, by the com- 

 mon mode of manipulation, is to be transferred from the tin platform to the shelf of the 

 trough for inspection. 



55. By this apparatus it was found that one thousand measures of atmospheric air, 

 exposed in a bubble to atmospheric air, in five successive experiments, underwent no 

 change either in volume or composition. The duration of the trials was severally ten, 

 fifteen, twenty, thirty, and sixty minutes, and the uniform result, when drawn back into 

 the under cupping-glass, was one thousand measures exactly, the composition of which 

 was the same as atmospheric air. 



56. The thermometer stood at 54 Fah. One thousand measures of hydrogen in 

 the watery film were subjected to atmospheric air in the upper bell; in five minutes 

 there remained only four hundred and seventy-two. In the second trial, one thousand 

 measures in twenty minutes became-four hundred and thirty-two ; and in a third, when 

 the same quantity of gas was confined half an hour, the residue was four hundred and 

 eighty measures. 



57. A reverse action ensues when nitrogen is substituted for hydrogen : the bubble 

 swells instead of diminishing, and the resulting gas measures more. It is to be remarked, 

 that after the first five minutes, provided the bubble has been sufficiently thin, there 

 appears to be little or no change in the volume of gas, and in a great many experi- 

 ments it was found that motion had ceased when the bubble had increased somewhere 

 between 7i and 10 per cent. The thermometer standing at 55 Fah., one hundred meas- 

 ures of nitrogen in half an hour became one hundred and seven and a half. In another 

 trial, two hundred measures in the same time became two hundred and fifteen. Again, 

 two hundred in fifteen minutes became two hundred and sixteen. The greatest varia- 

 tion from this was in one case, when, after an exposure of five hundred measures for 

 five minutes, the bubble was found to contain five hundred and forty-five measures, or 

 an increase of 9 per cent. 



58. Oxygen gas exposed in like manner to atmospheric air, decreased in bulk ; thus, 

 two hundred and fifty measures in ten minutes became one hundred and fifty-three, and 

 the like quantity in fifteen minutes diminished to one hundred and forty-four, which 

 amply proves that the passage of oxygen takes place through water more rapidly than 

 nitrogen. And upon this fundamental principle, chemical decompositions can be ef- 

 fected ; as in the last section, where we have a bubble of nitrogen gas exposed to the 

 atmosphere, the nitrogen outside parts with its oxygen, and passing through the barrier, 

 unites with the oxygen within. 



59. Having thus recognised a variation in the rate of passage of gases through thin 

 films, it becomes a point of investigation to ascertain how long these motions may be 



