274 Prof. Graham on the Law of the Diffusion of Gases. 



was filled with ammoniacal gas in the usual way, the final con- 

 traction was by no means excessive, indeed, never quite so 

 great as it should have been from diffusion alone, independ- 

 ently of the contraction from absorption. This was found to 

 arise from the absorption by the plug being so rapid, that, 

 during the progress of filling the tube with gas, the plug be- 

 came nearly saturated with gas, taking up ten or twelve times 

 its bulk, and consequently, a great deal more gas was intro- 

 duced into the tube than its capacity. 



9. Sulphuretted Hydrogen Gas. — Prepared from sulphuret 

 of antimony, by the action of muriatic acid. Density, 1*1805, 

 Root, 1-0855. Reciprocal of root, 0*9204. 



In the case of this gas, 69 measures were replaced by 73 air. 

 In this experiment, 100 air replaced 95 instead of 92 sulphu- 

 retted hydrogen. But we may refer the diminution to the ab- 

 sorption of the gas by the plug, and to its partial decomposi- 

 tion, as the mercury exposed to the gas became black. The 

 air which entered contributed to this decomposition. 



As carbonic acid is one of the gases condensed by the plug, 

 like the preceding examples, but to a less extent, we can now 

 understand why the return air was always a little under the 

 theoretical quantity, in the careful experiments on that gas, of 

 which an account was formerly given. 



- In the case of the gases which follow, the specific gravity 

 approaches so closely to that of air, that their accordance with 

 the law requires every precaution. 



10. Oxygen Gas, — Specific gravity, 1*111. Square root, 

 1*0541. Reciprocal, 0*9487. 



100 oxygen should be replaced by 105*41 air; and 

 100 air should replace 94*87 oxygen. 



When confined in a straight diffusion-tube, there is uni- 

 formly an expansion; but it is unnecessary to recount experi- 

 ments performed with the straight tube, as the divisions are 

 not minute. 



Experiment 1. — Thermometer 64°. Barometer 29*82 inches. 

 Diffusion-instrument with bulb, divided into two hundredths 

 of a cubic inch; also standard bulb and tube, close at top, to 

 afford corrections for changes in temperature and pressure, as 

 before explained. Both diffusion-instrument and standard were 

 filled with pure oxygen from chlorate of potash, and placed 

 in glasses over water, covered by a bell-jar, of which the in- 

 side was moistened. A few minutes were purposely allowed 

 to elapse before the quantity of gas in either instrument was 

 noted, as the quantity oscillated for a little. The diffusion- 

 instrument contained 795 measures oxygen, and the standard 

 828, at the outset. In two hours the expansion in diffusion- 



