40 



Prof. J. Emerson-Reynolds on Glucinum: 



The well-known law of Dulong and Petit, as modified by 

 Cannizaro, asserts that the atoms of elementary matter have 

 the same capacity for heat, when we compare them in the solid 

 state. The outstanding exceptions to this important law are 

 feAV ; and even these appear to have been cleared away in some 

 degree by the recent researches of Weber on the specific heats 

 of silicon, boron, and carbon. The principle, however, is ad- 

 mittedly sufficiently general in its application to enable us to 

 found upon it a plan for the determination of the atomic weight, 

 so called, of a particular element ; for it is evident that if we 

 employ as a standard a metal whose atomic weight and specific 

 heat are both accurately known — silver for example ( = 100) 

 — the weight of another solid element which contains the same 

 quantity of heat at 100° C. as 108 parts of pure silver at 100° 

 C. is the atomic weight of the element. In seeking to com- 

 pare glucinum with pure metallic silver in this way, I suc- 

 ceeded in arranging an experimental method which not only 

 enabled me to attain the object I had in view, but also to de- 

 monstrate the truth of the law just referred to. The apparatus 

 required is easily constructed, and consists of a spirit-thermo- 

 meter with a cylindrical "bulb " in which a test-tube is sealed, 

 after the manner of Bunsen's ice-calorimeter. This part of 



the apparatus can be conveniently made from a small chloride- 

 afford trustworthy results with small weights of material. I have given 

 in the text an outline of this method ; hut the details of its application to 

 the determination of atomic and molecular heat will form the subject of 

 another communication. 



