1863.] 619 



taming only 9 '3 per cent, of hydrogen, in which a taper burned with- 

 out explosion ; and with equal volumes of oxygen and hydrogen, the 

 proportion of the latter was easily reduced from 50 to 5 per cent. 



Interdiffusion of Gases double diffusion. The diffusiometer 

 was much improved in construction by Prof. Bunsen, from the 

 application of a lever arrangement to raise and depress the tube 

 in the mercurial trough. But the mass of stucco forming the 

 porous plate in his instrument was too voluminous, in my opinion, 

 and, from being dried by heat, had probably detached itself from 

 the walls of the glass tube. The result obtained of 3*4 for hy- 

 drogen, air being 1, is, I understand, no longer insisted upon by 

 that illustrious physicist. It is indeed curious that my old expe- 

 riments generally rather exceeded than fell short of the theoretical 



number for hydrogen, ^/ =3*7997. With stucco as the 



material, the cavities in the porous plate form about one-fourth of its 

 bulk, and affect sensibly the ratio in question, according as they are 

 or are not included in the capacity of the instrument. Beginning 

 the diffusion always with these cavities filled with hydrogen, the 

 numbers now obtained with a stucco plate of 12 millims. in thick- 

 ness, dried without heat, were 3783, 3*8, and 3*739 when the volume 

 of the cavities of stucco is added to the air and hydrogen, and 3*931, 

 3*949, and 3*883 when such addition is not made to these volumes. 

 The graphite plate, on the other hand, being thin, and the volume 

 of its pores too minute to require to be taken into account, its action 

 is not attended with the same uncertainty. With a graphite plate 

 of 2 millims. in thickness, the number for hydrogen into air was 

 3*876, and of hydrogen into oxygen 4*124, instead of 4. With a 

 graphite plate of 1 millim. in thickness, hydrogen gave 3*993 to air 1. 

 With a graphite plate of 0*5 millim. in thickness, the proportional 

 number for hydrogen to air rose" to 3*984, 4*068, and 4*067. A 

 similar departure from the theoretical number was observed when 

 hydrogen was diffused into oxygen or carbonic acid, instead of air. 

 All these experiments were made over mercury and with dried gases. 

 It appears that the numbers are most in accordance with theory when 

 the graphite plate is thick, and the diffusion slow in consequence. If 

 the diffusion be very rapid, as it is with the thin plates, something 

 like a current is possibly formed in the channels of the graphite, 



