420 



Dr. J. H. Long on the 



transferred to a platinum crucible and evaporated to dryness. 

 But this method was soon found to be inconvenient and very 

 inaccurate, as the weight of substance dissolved from the glass 

 vessels during the evaporation was about equal to that of the 

 diffused salt. For a similar reason, it was found unsafe to 

 evaporate in glass and precipitate with BaCl 2 . These sources 

 of error were finally avoided by evaporating the whole of the 

 liquid obtained in 24 hours in platinum dishes, then precipi- 

 tating with BaCl 2 , and weighing as BaS0 4 . The results of 

 the experiments are as follows, the values being reduced for 

 one cell: — 



Diffusion of 5 (NHJ a S0 4 . 

 1st day diffused 0*0491 gr. 



2nd 

 3rd 



0-0492 

 0-0463 



Mean 0-0482 gr. (JS T H 4 ) 2 S0 4 in 

 24 hours. 



Diffusion of "Na. SO,. 



1st dav diffused 0-0502 gr. 

 2nd „ „ 0-0481 „ 



3rd „ „ 0-0452 „ 



Mean 0-0478 gr. IS T a 2 S0 4 in 24 

 hours. 



Diffusion of -- ZnSO,. 



2 4 



1st day diffused 0-0298 gr. 

 2nd „ „ 0-0266 „ 



3rd „ „ 0-0243 „ 



Mean 0-0269 gr. ZnS0 4 in 24 

 hours. 



Diffusion of -"; CuS0 4 . 



1st day diffused 0-0271 gr. 

 2nd „ „ 0-0234 „ 



3rd „ „ 0-0250 „ 



Mean 0-0252 gr. Cu S0 4 in 24 

 hours. 



Diffusion of 1 MgS0 4 . 



1st day diffused 0-0243 gr. 

 2nd „ „ 0-0209 „ 



3rd „ „ 0-0184 „ 



4th „ „ 0-0183 „ 



Mean 0-0209 gr. MgS0 4 in 24 

 hours. 



Diffusion of £ MnS0 4 . 



1st day diffused 0-0230 gr. 



2nd „ „ 0-0231 „ 



3rd „ „ 0-0213 „ 



4th „ „ 0-0231 „ 



Mean 0-0226 gr. MnS0 4 in 24 

 hours. 



What are here spoken of as the 1st, 2nd, and 3rd days are 

 in reality the 3rd, 4th, and 5th days of the experiment, two 

 days being allowed to pass before the determinations were 

 commenced. 



Considering all the experiments given above in detail, it 

 will be seen that, as a rule, the progress of the diffusion from 

 day to day was pretty regular, the fluctuations not being 

 greater than one might expect. The sulphates show the 

 greatest irregularities ; and it would seem from the results 



