the Diffusion of Gases. 229 



instrument. We thus obtain the equivalent diffusion-volume of 

 the gas, which it will be convenient to state in numbers, with 

 reference to the replacing volume of air as unity. I shall begin 

 with hydrogen gas, although attended with peculiar difficulties, 

 as it introduces in a distinct manner to our notice several cir- 

 cumstances which may slightly modify the results of diffusion. 



1. Diffusion-volume of Hydrogen Gas. 



I shall in this paper adopt the specific gravities of the gases 

 generally received in this country. Of hydrogen the specific 

 gravity is 0.0694 (air 1), of which number the square root i? 

 0.2635. Now, according to our law, 1 volume hydrogen should 

 be replaced by 0.2635 air. But to have the replacing volume of 

 air =. 1, 



0.2635 :!::!: 3.7947 ; 

 or, 7737^- = 3.7947 ; that is, 1 air should replace 3.7947 hy- 



drogen. With the specific gravity of hydrogen adopted by BER- 

 ZELIUS, namely, 0.06885, the equivalent diffusion-volume of hy- 

 drogen is 3.81 49. 



In a diffusion-tube standing over water, temperature 65, 88 

 volumes hydrogen were replaced by 26 air ; 84 hydrogen by 25 

 air; and in another tube, 130 hydrogen by 38 air. The quan- 

 tity of return-air is here related to the hydrogen diffused, as 1 

 to 3.38, 3.36, and 3.42, numbers which approach to, but fall 

 short of, the theoretical diffusion-volume of hydrogen, namely, 

 3.79. But the hydrogen in these experiments was saturated 

 with vapour at 65, which would make its density 0.0809, and 

 reduce its diffusion-volume to 3.5161 ; while the air without, 

 being comparatively dry, would be somewhat expanded after it 

 entered the diffusion-tube, by the ascent of vapour into it. This 

 would occasion the quantity of return-air to appear greater than 



VOL. XII. PART I. G g 



