808 
PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
These experiments indicate a similarity of diffusion between the two isomorphous 
substances, hydrochloric and hydriodic acids. 
Diffusion from 2 per cent, solutions at 51° Fahr. 
Hydrochloric acid 15*04 100 
Hydriodic acid 15*11 100*46 
Hydrohromic Acid . — Time of diffusion five days. The diffusate was estimated from 
the bromide of silver. 
(1.) Hydrobromic acid, 1*556 per cent. ; density 1*0112. Diffused at 59°*7, in eight 
cells. The whole diffusates mixed together gave by analysis a mean of 12*90 grs. of 
hydrobromic acid in two cells ; calculated for 2 per cent., 16*58 grs. in two cells, at 
59°*7. 
(2.) The experiment was repeated at 59°*8, with a solution containing T578 per 
cent, of hydrobromic acid, of density 1*0116, with five diffusion phials not employed 
above. The mean diffusate for a pair of cells was 13*05 grs. of hydrobromic acid ; 
that is, 16*53 grs. for a 2 per cent, solution, which is as nearly as possible the result 
of the preceding series of experiments. 
(3.) Another solution containing exactly 2 per cent, of hydrochloric acid was dif- 
fused for comparison in eight cells, in the same circumstances of time and tempera- 
ture as (1.) ; its density was 1*0104. 
Diffusate from 2 per cent, solutions at 59°*7 Fahr. 
Hydrochloric acid 16*55 100 
Hydrobromic acid 16*58 100*18 
Hydrobromic acid appears therefore to coincide in diffusibility with hydrochloric 
acid at this temperature. It may be remarked that these three acids, hydrochloric, 
hydrobromic and hydriodic, do not exhibit the same correspondence in another phy- 
sical property, namely, the densities of their aqueous solutions containing the same 
proportion of acid. The densities of 2 per cent, solutions of hydrochloric and hydri- 
odic acids appear to be respectively 1*0104 and 1*0143, at 60° Fahr., and that of 
hydrobromic acid will obviously be an intermediate number. The same acids are 
also known to differ considerably in the boiling-points of solutions containing the 
same proportion of acid. A considerable diversity of physical properties appears here 
to be compatible with equal diffusibility in substances which are isomorphous. 
Bromine . — Pure water readily dissolves more than 1 per cent, of this substance. 
The solution prepared, however, contained only 0*864 per cent, of bromine, as was 
ascertained by treating it with sulphurous aeid and afterwards precipitating by 
nitrate of silver. Its density was 1*0070. It was evident, from the slow appearance 
of the brown colour in the exterior cell, that bromine diffuses less rapidly than hydro- 
bromic acid. 
