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VI.- -BAKEIUAN LECTURE. The Specific Heats of Metals, and the Relation of 



Specific Heat to Atomic Weight. 



liy W. A. TILDEN, D.Sc., F.R.S., Professor of Chemistry in the Royal College of 



Science, London. 



With an Appendix by Professor JOHN PERRY, F.R.S. 

 Received February 9, Read March 8, 1900. 



THE experiments recorded in the following pages were begun nearly five years ago, 

 at a time when opinion was still much divided as to the atomic weight of cobalt and 

 nickel. It seemed to me that it would be a step in advance if it could be settled 

 which of the two is the greater, for while perhaps the majority of chemists represented 

 the atomic weight of cobalt as greater than that of nickel, some still assigned to them 

 both the same value, while MENDELEEFF* did not- hesitate to invert the order by 

 making Co = 58 '5 and Ni = 59. After taking into account all the best evidence on 

 the subject, it appears certain that the atomic weight of cobalt is greater than that of 

 nickel, but the fact remains that the values differ from each other by an amount 

 which is less than the difference between any other two well established atomic 

 weights, the respective numbers l)eing variously represented by different authorities 

 as follows : 



The object of my experiments, however, soon developed into a wider field, for it 

 appeared that the results obtained with these two metals might be made the means 

 of further testing the validity of the law of DULONG and PETIT, inasmuch as 

 temperatures at which the specific heats would be determined are not only very 

 remote, but about equally remote, from the melting points of these two metals. 



* ' Principles of Chemistry ' (English translation, 1891), vol. 2, p. 333, and table at beginning. 

 t ' Amer. Chem. J.,' vol. 20, p. 543, 1898. 

 t ' Ber. d. Deutsch. Chem. Gesell.,' vol. 31, p. 2761, 1898. 

 VOL. CXCIV. - - A 257. 2 H 9.6.1900 



