830 
PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
at 59°‘8, in eight cells, it gave a mean dilfusate of 12-30 grs. for two cells ; or ] 2-46 grs. 
for 2 per cent. 
For comparison, a solution of chloride of potassium^ containing exactly 2 per cent, 
of salt and having the density TO 133, was diffused in the same circumstances of time 
and temperature as the two preceding salts. The mean diffusate of eight cells was 
12*24 grs. for two cells. 
Hence the following result of the diffusion of three isomorphous salts : — 
Diffusion of 2 per cent, solutions in 5*716 days, at 59°*8. 
Chloride of potassium . . 
Grs. 
. . 12*24 
Ratio. 
100 
Bromide of potassium . . 
. . 12*46 
101*80 
Iodide of potassium . . . 
. . 12*51 
102*21 
Mean . . 
. . 12*40 
Iodide of Sodium. — Time of diffusion 7 days, temperature 59°*8. A solution of 
2*011 per cent, and density 1*01618, diffused in eight cells, gave a mean diffusate of 
12*24 grs. for two cells ; that is, 12*18 grs. for 2 per cent, solution. 
Bromide of Sodium. — Time of diffusion and temperature as above. A solution of 
2*146 per cent., of density 1*01726, diffused in eight cells, gave a mean diffusate of 
12*80 grs. ; that is, 1T93 grs. for 2 per cent. 
A comparative experiment was made with a solution of chloride of sodium, contain- 
ing 1*917 per cent, of salt and of density 1*01376, in eight cells, at 60°. The diffusates 
for four pairs of cells were 11*65, 11*75, 11*63 and 11*47 gi'S.; mean 1 1*63 grs., which 
gives by proportion 12*14 grs. for a 2 per cent, solution. As the present salt differs 
only 0°*2 Fahr. in diffusion-temperature from the two preceding salts, which is in- 
adequate to produce an assignable difference of diffusion, the three salts may be sup- 
posed to be diffused at the same temperature, without sensible error. 
Diffusion of 2 per cent, solutions for 7 days. 
Chloride of sodium at 60° . . . 
Grs. 
. 12*14 
Ratio. 
100 
Bromide of sodium at 59°*8 . . 
. 11*93 
98*27 
Iodide of sodium at 59°*8 . . . 
. 12*18 
100*33 
Mean . . . 
. 12*08 
In both these isomorphous groups of salts of potassium and sodium, there is certainly 
a near approach to equality of diffusion. The times for the salts of the two bases 
being in the empirical proportion of the square roots of 2 and 3, the mean diffusates 
also approach pretty closely; namely, 12*40 grs. for the salts of potassium and 12*08 grs. 
for the salts of sodium, which are as 100 to 97'42. Here the members of each group 
are certainly very similar to each other in density and probably other physical pro- 
