118 Specific Heats of Cerium, Lanthanum, and Didymium. 



In order to determine the composition of the metal under 

 investigation, 0*7946 grm. of it was dissolved in nitric acid 

 and the resulting nitrate ignited ; the residual oxide of cerium 

 weighed 0*9768 grm. By treatment with concentrated sul- 

 phuric acid and repeated evaporation with sulphurous acid 

 1*6303 anhydrous cerous sulphate was obtained, which, on 

 solution, left a residue, consisting of 0*0031 grm. of silica 

 and 0*0127 ferric oxide, which was found to be free from oxide 

 of cerium and alumina. 



The amount of didymium was determined by spectral ana- 

 lysis as above described; it was estimated at 0*0332 grm. 

 The cerous sulphate, when converted into cerous chloride and 

 tested in the electric spark before the spectroscope, exhibited 

 only a few very weak lines of the lanthanum spectrum. The 

 eerie oxide obtained by the oxidation of the metal contained in 

 100 parts:— 



Oxide of cerium . . . . =94*98 

 Oxide of didymium . . . = 3*40 

 Oxide of iron . . . . = 1*30 

 Silica = 0*32 



100*00 



Since 0*9768 grm. of this impure eerie oxide was obtained 

 from 0*7946 grm. of the impure cerium metal, 100 grms. of 

 the above oxide must contain 81*347 grms. of the impure metal. 

 By subtracting the amount of the metals contained in the 

 impurities, we have, out of 94*98 grms. of pure eerie oxide, 

 77*362 grms. of pure cerium metal. 



The composition of the ignited oxide obtained after treat- 

 ment of the pure metal with nitric acid as directly found is 

 therefore 



Cerium 81*45 



Oxygen 18*55 



100*00 



According to very careful experiments upon chemically pure 

 cerous sulphate, which were performed in Professor Bunsen's 

 laboratory some time ago by C. Wolf, this salt contains 



Cerous oxide .... =57*294 

 Sulphuric acid .... =42*706 



100*000 



On the purely hypothetical assumption that in this salt the 

 quantity of oxygen is one third of that contained in the sul- 

 phuric acid needed for combination, it follows that the compo- 

 sition of the highest oxide of cerium is 



