52 GASES PASS WHEN RESISTED BY THE FORCE OF MANY ATMOSPHERES. 



a test, in the upper part of the arrangement, and in lieu of the tube f, I placed a slip 

 of paper, which had been alternately soaked in acetate of lead and carbonate of soda ; 

 the India-rubber was fortified by a piece of very strong silk, which was carefully tied 

 on; there was not, therefore, any gaseous matter present except the small quantity of 

 atmospheric air in the gauge-tube. The condensation, therefore, went on with great 

 rapidity, a mixture of oxygen and hydrogen gradually accumulating in the top of the 

 vessel, bulging out the India-rubber and silk barrier until it was almost hemispherical. 

 It was my intention to try a pressure of twenty-five atmospheres; and when that was 

 supposed to be reached, the instrument was placed in an atmosphere of sulphuretted 

 hydrogen. Very soon the test paper became of a tawny appearance, and, finally, it was 

 quite J)lack. The pressure, when the experiment was over, was found to be twenty- 

 four and a quarter atmospheres. 



163. At a temperature of 48 F., and pressure of 29-74 B., sulphuretted hydrogen 

 gas passes into a mixture of oxygen and hydrogen, though it may be resisted by a pres- 

 sure of twenty-four and a quarter atmospheres, or nearly seven hundred and thirty 

 inches of mercury. Like sulphurous acid, it penetrates through a barrier, and then dif- 

 fuses into an atmosphere beyond it, at pressures greater than that which is necessary 

 to condense it into a liquid. 



164. If, as it thus appears, no pressure which we can command is sufficient to re- 

 strain one gas from passing into another, we next inquire what obstacle the condensed 

 gas exhibits. There is abundant and conclusive evidence that, under ordinary circum- 

 stances of temperature and pressure, this medium bears the same relation to the perco- 

 lating gas that a vacuum would do ; inasmuch as the rate of discharge into it is iden- 

 tically the same as it is into a vacuum. For the purpose of illustration, we may, there- 

 fore, regard it to all intents as a vacuum, and reason accordingly. If the particles of 

 heterogeneous gases possess no repulsive tendency as respects each other, but are per- 

 fectly quiescent and neutral ; if the presence or absence of one makes no difference nor 

 produces any retardation on the motions of the particles of the other, then it is appa- 

 rent that it is immaterial how many of such particles are condensed together into a given 

 space ; owing to the want of repulsive action in those particles, that space will be as 

 much a vacuum to any other gas as it ever was. Now it has been shown by the ex- 

 periment above cited, that certain gases will diffuse into others, even though the latter 

 may be condensed into a space twenty-four times less than that which they would or- 

 dinarily occupy. The vacuum is not less a vacuum because it is contained under smaller 

 dimensions, any more than a torricittian vacuum is less perfect when the mercury is 

 made to rise nearly to the top of the barometric tube, than it was ivhen there was a va- 

 cant space many inches in length. Theory would therefore indicate that these diffusions 

 will take place under all pressures, provided the gaseous condition subsists; and this 

 conclusion is abundantly borne out by the experiments herein detailed. 



165. Having thus shown how it is that, when gaseous matter is on one side of a 

 barrier, the space so occupied may be regarded as a vacuum, even though the gas should 

 be highly condensed, I come next to the consideration of a much more intricate part of 

 the subject, the action of the barrier itself as an areolar tissue, which is the more imme- 



