PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
43 
phates and nitrates, but agree perfectly with each other, showing a uniformity in their 
irregularity. This deviation of the carbonates would appear essential, as it has been 
observed every time they have been compared with the sulphates. 
The double relation between salts of potash and salts of soda, and between the 
nitrate and sulphate class of each of these bases, will, I believe, be allowed to acquire 
considerable additional support from this new series of observations. 
IV. DIFFUSION OF SULPHATE OF MAGNESIA. 
In a set of preliminary experiments upon sulphate of magnesia in comparison with 
sulphate of potash, the 4 per cent, solutions of both salts were diffused for seven days 
at a mean temperature of 57°‘9, with very little fluctuation, the extreme range being 
from 58°’5 to 57°‘75. The sulphate of magnesia is taken anhydrous in all the follow- 
ing experiments. The diffusion of sulphate of potash in three cells was 9T6, 9 22 and 
9’57 grs. ; mean 9 32 grs. 
The diffusion of sulphate of magnesia in three cells was 5*21, 4*98 and 5*34 grs. ; 
mean 5*18 grs. The diffusion, in equal times, appears here to be as 100 sulphate of 
potash to 55*58 sulphate of magnesia. We know, however, when unequally dif- 
fusible salts are diffused for equal times, that the diffusion of the slower is exagge- 
rated. Consequently the diffusion of sulphate of magnesia is likely to be represented 
in excess in these experiments. 
In a second preliminary series of experiments the same 4 per cent, solutions were 
diffused, the sulphate of potash for eight days and the sulphate of magnesia for nine- 
teen days, with the view of discovering their times of equal diffusibility. 
During the first period of eight days the temperature fluctuated considerably, be- 
ginning at 54°, falling gradually in four days to 50°*5, and rising again in four days 
to 53° ; the average of the whole period was 52°*2. The diffusion of sulphate of pot- 
ash from three cells was 9*36, 9*25 and 10*52 grs.; mean 9*71 gi’S. 
During the second period of nineteen days, which included the first period, the 
mean temperature was 54°*6. The diffusion of sulphate of magnesia from three cells 
was 1 1*81, 1 T61 and 10*90 grs. ; mean 11*44 grs. The variation in the amounts dif- 
fused of both salts is greater than usual, owing no doubt to the changes of tempera- 
ture, which were imperfectly controlled. 
Dividing the quantity of salt diffused by the number of days, we have of sulphate 
of potash 1*214 gr. diffused per day, and of sulphate of magnesia 0*602 gr. per day; 
or the latter salt exhibits sensibly half the diffusibility of the former in equal times. 
This suggested the trial of times for these two salts in the proportion of 1 to 2, with 
the view of obtaining equal diffusions. 
(1.) A one per cent, solution of sulphate of magnesia (anhydrous) was diffused for 
the long period of 19*8 days, at a mean temperature of 54°*75 in eight cells. The dif- 
fusion products of four pairs of cells were 7*07, 6‘71j 7'07 and 7’35 grs.; mean 7’05 
grs., or for one cell, 3*53 grs. 
