Specific Heats of Cerium, Lanthanum, and Didymium. 109 



found in nature, and indicate that the term " preposterous," 

 employed by the late Mr. Scrope in reference to my views, 

 was misapplied. My main object in addressing you here is 

 to call the attention of any competent observers who may 

 visit Iceland during the summer of next year, so that a fuller 

 and better account as regards the circumstances and conditions 

 of this alleged conversion of geyser into volcano may be ob- 

 tained. 



1 am, Sir, 



Your obedient servant, 



Robert Mallet. 



London, December 30, 1876. 



XVI. On the Specific Heats of Cerium, Lanthanum, and 

 Didymium. By Dr. W. F. Hillebrand *. 



THE following investigation has been made with the metals 

 separated by electrolysis by Dr. Norton and myselff , 

 under the kind superintendence of Professor Bunsen, whose 

 ice-calorimeter we have made use of. 



The larger fragments of the metals (some of which weighed as 

 much as 6 grms.) were most free from impurities, since the 

 smaller globules, by failing through the mass of the fused chlo- 

 rides, were apt to adhere to the sides of the porous cell, and to 

 become contaminated with perceptible quantities of its material. 

 Notwithstanding that this fact indicated that it was desirable 

 to make use of the larger pieces of metal, I nevertheless hesi- 

 tated to break up those beautiful preparations, rather prefer- 

 ring to employ the smaller and less pure specimens, and to de- 

 termine the nature of the impurities after the specific heat 

 had been ascertained and to make allowance for their effect. 

 Since the metals under consideration are rapidly oxidized on 

 exposure to air and decompose water, it was necessary to 

 enclose them in a glass envelope. Accordingly it was first 

 necessary to determine the amount of heat which 1 grm. of 

 the glass employed gives out in cooling from 1° C. to 0° C. 



This, Wg4, is given by means of the equation 



T 

 W = — 



g %t 



from the following experiments: — 



* From Pogg. Ami. der Pliys. u. Chemie, vol. clviii. p. 71. Translated 

 by Mr. John I. Watts, the Owens College, Manchester, 

 f Pogg. Ami. vol. clvi. p. 466. 

 X Pogg. Ann. vol. cxli. p. 19. Phil. Mag. [IV.], vol. xli. p. 161. 



