CERIUM. 383 



protoxide of cerium in the salt, and must also be 

 the atomic weight of that protoxide. 



From the preceding analysis the reader will 

 perceive, that protosulphate of cerium is com- 

 posed of 



1 atom sulphuric acid . 5 

 1 atom protoxide of cerium 7*25 

 3 atoms water . . 3-375 



15-625 



7 -25, then, is the true atomic weight of protoxide Atom of 



f, . ,, 111-11 i protoxide 



or cerium, which is a little higher than the num- of cerium, 

 ber deduced from Hisinger's analysis of the 

 muriate of cerium. The probable reason for 

 this difference has been already hinted at. 



5. According to Hisinger's experiments the 

 oxygen in the protoxide of cerium is to that in 

 the peroxide as 2 to 3. My stock of cerium 

 was not sufficient to enable me to make a simi- 

 lar set of experiments on peroxide of cerium, of per - 

 But there is every reason to confide in the ratios cerium. 

 which Hisinger has deduced from his analyses ; 

 all of which, having been made in the same 

 way, would be subject to the same errors, which 

 would not affect the ratios between the two 

 oxides, though it had an effect upon their abso- 

 lute weights. It is easy from these ratios to de- 

 duce the atomic weights and composition of 

 cerium and its oxides, as follows : 



