Prof. Graham on the Diffusion of Liquids, 345 



equal times, appears here to be as 100 sulphate of potash to 

 55*58 sulphate of magnesia. We know, however, when un- 

 equally diffusible salts are diffused for equal times, that the 

 diffusion of the slower is exaggerated. Consequently the dif- 

 fusion 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 nineteen days, 

 with the view of discovering their times of equal diffusibility. 



During the first period of eight days the temperature fluc- 

 tuated considerably, beginning at 54°, falling gradually in four 

 days to 50°*5, and rising again in four days to 53°; the ave- 

 rage of the whole period was 52°*2. The diffusion of sulphate 

 of potash from three cells was 9'36, 9*25 and 10*52 grs. ; 

 mean 9*71 grs. 



During the second period of nineteen days, which included 

 the first period, the mean temperature was 54°*6. The dif- 

 fusion of sulphate of magnesia from three cells was 11*81, 

 11*61 and 10*90 grs.; mean 11*44 grs. The variation in the 

 amounts diffused of both salts is greater than usual, owing no 

 doubt to the changes of temperature, 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 dif- 

 fusions. 



(1.) A one per cent, solution of sulphate of magnesia (an- 

 hydrous) was diffused for the long period of 19*8 days, at a 

 mean temperature of 54°*7, in eight cells. The diffusion 

 products of four pairs of cells were 7*07, 6*71, 7*07 and 7*35 

 grs.; mean 7*05 grs., or for one cell, 3*53 grs. 



A similar solution of sulphate of potash diffused for 9*9 

 days, or half the preceding period, at a mean temperature of 

 55°*4, or 0°*7 higher, gave a mean product, for two cells, of 

 6*79 grs., as before stated, or for one cell, of 340 grs. The 

 diffusion of sulphate of potash being 100, that of sulphate of 

 magnesia is therefore 103*7, a fair approximation to equality. 

 (2.) In a second series of experiments upon 1 per cent, 

 solutions of the same two salts, diffused in the vault for four- 

 teen and seven days respectively, with a mean temperature of 

 53° # 8 for the sulphate of magnesia, and 54°*3 for the sulphate 

 of potash, the temperature was remarkably uniform, gradually 



