1835.] Chemical Analysis of Gadolinite, Sfc. 419 



The residual solution was mixed with nitric acid in excess 

 and precipitated by chloride of barium. The sulphate of 

 barytes collected on a filter, well washed, dried and ignited 

 weighed 18*53 grs. =6*42 grs. of sulphuric acid. This 

 analysis gives, 



Peroxide of cerium ... 8-893 or 6-92 

 Sulphuric acid .... 6-420 „ 5* 

 Water 4-2 „ 3-25 



19-513 

 Increase of weight by the peroxidizement of the cerium, 

 0-513 grs. 



These analyses give as the atomic weight of the peroxide 

 of cerium, 1st. . . 7-15 



2nd. . . 7-10 

 3d. . . 6-92 

 Mean . 705 

 This mean comes so near 7 as to leave little doubt that 

 it is the true number. The increase of weight of the oxide 

 in each analysis comes very near half an atom of oxygen. 

 The reason why it is not exactly so, is that we were unable 

 to render the salt perfectly anhydrous, without decomposi- 

 tion. It is pretty evident then that the atomic weight of 

 protoxide of cerium is 6*5, and that the true composition of 

 cerium is doubtless, 



1 atom protoxide . . . 6*5 

 1 atom sulphuric acid . 5* 

 3 atoms water .... 3*375 



14-875 



2. Sulphated Peroxide of Cerium. — This salt may be 

 obtained by dissolving peroxide of cerium in dilute sulphuric 

 acid by a gentle heat. The solution takes place slowly. 

 The orange coloured solution thus formed, when cautiously 

 evaporated, yields beautiful silky needles of a lemon-yellow 

 colour. When alcohol is added to the concentrated solu- 

 tion the salt falls down exactly like a piece of soft yellow 

 resin, very adhesive, not exactly deliquescent, but becoming 

 softer when exposed to the air. 



The crystals are quite permanent in the air. When dis- 

 solved in a small quantity of water they are decomposed 



2e2 



