of Cerium, Lanthanum, and Didymium. 115 



Hence we have for the specific heat of lanthanum : — 



From Exp. I. . . . 0*04582 



From Exp. II. . . . 0*04692 



Mean . . . 0*04637 



The metallic lanthanum employed in these experiments was 

 likewise not quite pure. It was obtained from chloride of lan- 

 thanum after the larger globules of lanthanum had been sepa- 

 rated, and in which the traces of didymium originally present 

 had become concentrated, since lanthanum is more easily sepa- 

 rated by the current than didymium. 0*8911 grm. of the 

 same specimen which had been employed in the foregoing ex- 

 periments, when oxidized with nitric acid, gave 1*0516 grm. 

 of oxide of lanthanum, which, on solution in hydrochloric acid, 

 evaporation, and re-solution, left 0*054 grm. of silica. 



All the oxides were precipitated from the liquid by means 

 of ammonia and filtered off; the filtrate, after evaporation and 

 ignition, gave in addition a few milligrams of oxide of lan- 

 thanum. By digesting the hydrates with oxalic acid an inso- 

 luble white residue of the oxalates of lanthanum and didymium 

 was obtained, which, after ignition, together with the above- 

 mentioned small residue, gave 1*0276 grm. of oxide of lan- 

 thanum containing didymium, and, on the other hand, a 

 solution which, after evaporation and ignition, left a residue 

 consisting of 0*0156 grm. of ferric oxide, 0*0026 grm. of alu- 

 mina, and 0*0004 grm. of oxide of lanthanum. 



The amount of oxide of didymium associated with the lan- 

 thanum oxide was determined by means of the photometric 

 spectral method originally applied by Professor Bunsen. 



For this purpose a solution was prepared which, in Y 1 cubic 

 centimetres, contained g 1 grm. of pure sulphate of didymium 

 free from lanthanum. The 1*0276 grin, of oxide of lanthanum 

 which was to be tested for the amount of didymium which it 

 contained, was then dissolved in sulphuric acid, and gradually 

 mixed with so much water that both solutions, tested before 

 the spectroscope in equally thick layers, showed the didymium 

 bands of equal intensity. When this point was attained the 

 volume V of the liquid was read off. From these data we ob- 

 tain the amount of didymium g by means of the equation 



V 



The experiment ga^ve 



Y 1 = 25*7 cubic centims. 

 V =23*5 

 g 1 =0*0520. 



12 



