38 
PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
3'51 and 3'63 grs. ; mean for two cells, 3*50 grs., or exactly the same as for nitrate of 
potash above. 
(b.) Nitrate of potash diffused for seven days, at 48°'6, gave 61, 6 2, 5‘9 and 5'92 
grs. ; mean for two cells, 6'04 grs. 
Sulphate of potash diffused for 9'9 days, at 49°' 1, gave 6*13, 5'92, 6' 18 and 6*59 grs. ; 
mean 6‘20 grs., or, excluding the last experiment, 6’08 grs. 
Chromate of potash diffused also for 9’9 days, at 49°’ 1, gave 6’ 19, 6* 18, 6'40 and 
6’38 grs. ; mean for two cells, 6'29grs. The diffused chromate presented no appear- 
ance of decomposition on this occasion. 
(c.) Nitrate of potash diffused for 10’5 days, at 48°, gave 8’36, 8’95, 8’82 and 8*84 
grs. ; mean for two cells, 8*74 grs. 
Sulphate of potash diffused for 14*85 days, at 48° 6, gave 8*99, 8*94, 8*66 and 8*56 
grs.; mean for two cells, 8*79 grs. 
The mean results for the three different sets of periods of diffusion are as fol- 
lows *. — 
„ ^ ^ , f Nitrate of potash, at 47°'2, 3*50 grs. . . . 100 
^^ISulphateofpotash, at47°*3, 3*50grs. ... 100 
r Nitrate of potash, at 48°*6, 6*04 grs. . . . 100 
7 and 9*9 days^ Sulphate of potash, at 49°*1, 6*20 grs. . . . 102*65 
LChromate of potash, at 49°*1, 6*29 grs. . . 104*14 
r Nitrate of potash, at 48°, 8*74 grs 100 
10*5 an 14*85 cays ^ 
The concurring evidence of these three series of experiments appears to be quite 
decisive in favour of the assumed relation of 1 to 1*4142, between the times of 
equal diffusion for the nitrate and sulphate of potash, and consequently of the times 
for the two classes of potash salts, of which the salts named are types. The same 
experiments are also valuable as proving the similarity of the progression of diffusion, 
in two salts of unequal diffusibility. I shall return again to the relation between 
nitrates and sulphates, under the salts of soda. 
(8.) Hydrate of Potash. 
(1.) Eight cells of the 1 per cent, solution of pure fused hydrate of potash were 
diffused for seven days in the vault, with a temperature ranging only from 59° to 58°, 
of which the mean was 58°*6. The product of four cells evaporated together was 
17‘57 gi’S. of hydrate of potash, and of the other four cells 17’19 grs.; mean 17*38 
grs., or 4*345 grs. for one cell. The hydrate of potash was estimated from the chlo- 
ride of potassium which it gave when saturated with hydrochloric acid. The diffu- 
sion product of sulphate of potash for seven days, at 58°*5, or almost the same tempe- 
rature, was 10*75 grs. for the four cells, as already stated, and consequently 2*64 grs. 
for one cell. It thus appears that the hydrate of potash is greatly more diffusive than 
the sulphate of potash in the same period of seven days, namely, as 4*345 to 2*64. 
