734 Proceedings of the Royal Irish Academy. 



stem, a piece of pure silver ■weighing 108 centigrammes, and heated 

 to 100° C. in steam, is rapidly dropped into the cubic centimetre of 

 water, and the expansion caused in a given time carefully noted. '^^ 

 According to the law above stated, a centigramme atom, if I mav use 

 the term, of any other metal than silver ought to cause exactly the 

 same expansion, when the experiment is made with it under precisely 

 the same conditions ; and these conditions are very easily realised. 

 I have ascertained that such is the case, and the approximate equality 

 in " atomic heat " of many of the metals has thus been easily demon- 

 strated. 



The comparison of glucinum with silver was made on this plan,, 

 and it was found that the weight of glucinum which contains nearly the 

 same quantity of heat at 100° C. as 108 centigrammes of silver at the 

 same temperature, is not 4*6 or 4*6 x 3, but 4'6 x 2, or 9-2 centi- 

 grammes. 



The " atomic heat" of silver, or the product of the specific heat 

 (= -05701 according to Eegnault), into the atomic weight (= 108) 

 is 6-157. Using this number as the standard for reference, the 

 experimental number found for the atomic heat of the specimen of 

 glucinum operated with is 5-91. Thus : — 



Atomic heat of silver = 6-157 



Atomic heat of glucinum = 5-910 



The difference is less than the known difference between the 

 atomic heat of silver and that of aluminium ; but I am inclined to 

 think that the lower number found for the glucinum used is due to 

 the presence of a trace of platinum in the specimen of metal. Owing- 

 to the high atomic weight of platinum (= 197-1), as compared with 

 that of glucinum (9'2), the presence of even a small quantity of the 

 former metal must very sensibly affect the determination of the 

 atomic heat of glucinu.m. I hope soon to be in a position to continue 

 these experiments with the ^j?</-e metal. 



It will, however, appear from the following considerations that 

 we may fairly regard the above determination of the atomic heat of 

 glucinum as being of such value as to enable us, even at an early 

 stage of the inquiry, to use it as a physical control, and to fix the 

 atomic weight of the metal, subject of course to the probably small 

 change in the nu.merical expression which may prove to be necessary 

 as the investigation proceeds. 



If we assume the atomic weight of glucinum to be 9*2 and employ 

 the value I have obtained for the atomic heat, i. e., 5-91, we can cal- 

 culate the specific heat of the metal by means of the formula. 



* The apparatus is carefully protected from the influence of air currents diu-inj 

 the experiment. 



