986 



55*88 grs. of sesquichloride of iron, with 6*66 grs. of free hydro- 

 chloric acid, in two cells. It appears from this that percliloride of 

 iron approaches the chloride of calcium in diffusibility. That the 

 proto- and persalts of the magnesian metals should have a similar 

 rate of diffusion, is not unlikely from other analogies which they 

 exhibit. 



Sulphates of Magnesia and Zinc. — The time chosen for the dif- 

 fusion of these salts, namely, days, is a multiple by 2 of the 

 time of sulphate of potash, and by 4 of the time of hydrate of potash. 

 The diffusate was evaporated to dryness and weighed. 



Diffusion of sulphate of magnesia in 16'16 days at 65^'^ \ two 



cells : — 



Grs. Ratio. 



From 1 per cent, solution 7*31 1*144^ 



From 2 per cent, solution 12*79 2 



From 4 per cent, solution 23*46 3*671 



From 8 per cent, solution 42*82 6*701 



From 8 per cent, solution at 62°*8. . 42-66 1 

 From 16 per cent, solution at 62°*8. . 75*06 1*759 

 From 24 per cent, solution at 62°*8. . 102-04 2*340 



Diffusion of sulphate of zinc in 16*16 days at 65°*4; two cells: — 



Grs. Ratio. 



From 1 per cent, solution 6*67 1*091 



From 2 per cent, solution 12*22 2 



From 4 per cent, solution 23*12 3*784 



From 8 per cent, solution 42*26 6*916 



From 8 per cent, solution at 62°*8. . 39-62 1 

 From 16 per cent, solution at 62°*8. . 74*40 1*878 

 From 24 per cent, solution at 62°*8. . 101*42 2*560 



It is remarked that the diffusion of these two isomorphous salts, 

 sulphate pf magnesia and sulphate of zinc, differs so much, in the 

 1 per cent, solution, as 8*75 per cent. This, however, is considered 

 to be an accidental error, the disturbances from changes of tempe- 

 rature and other causes of dispersion being in direct proportion to 

 the duration of the experiment, and therefore much increased with 

 long times ; while the 1 per cent, solution also, from its low density, 

 is the proportion most exposed to such errors. The sulphate of zinc 

 appears to be the truest throughout, in its diffusion, of these two 

 salts. The approach to equality becomes close in the 4 per cent, 

 and larger proportions of salt, particularly with the unusually high 

 proportions of 16 and 24 per cent., which were observed in these 

 salts. The diffusion of both salts falls off remarkably in the higher 

 proportions. The result of the comparison of these two magnesian 

 sulphates is no doubt favourable to the similarity of diffusion of 

 isomorphous salts. 



Sulphate of Alumina. — The time of diffusion was the same as that 

 for sulphate of magnesia. 



Diffusion of sulphate of alumina in 16^166 days at 65°*4; two 

 cells : — 



