[ 316 ] 

 XLIV. Proceedings of Learned Societies. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



Feb. 3, "f'^N Aluminium Ethide and Methide." By William Od- 

 1865. ^ ling, M.B., F.R.S. 



The symbols by which the atomic proportions of a few of the prin- 

 cipal metallic elements are usually represented, together with the 

 relative weights of these several proportions, are shown in the fol- 

 lowing Table : — 



Lithium Li 7 



Magnesium . . . Mg 24 



Zinc Zn 65 



Arsenic As 75 



Silver Ag 108 



Tin Sn 118 



Mercury .... He: 200 



Lead PlT 207 



Bismuth Bi 210 



It is observable that the atomic proportions of the metals range 

 from 7 parts of lithium, through 108 parts of silver up to 210 parts 

 of bismuth. Now it is found that all these different proportions have 

 substantially the same specific heat, so that 7 parts of lithium, 108 

 parts of silver, and 210 parts of bismuth, for instance, absorb or 

 evolve the same amount of heat in undergoing equal increments or 

 decrements of temperature. Hence, taking silver as a convenient 

 standard of comparison, the atomic proportion of any other metal 

 may be defined to be that quantity of the metal which has the same 

 specific heat as 108 parts of silver. 



Many of the metals unite with the halogen radicals chlorine and 

 bromine, as also with the organic radicals ethyle and methyle, to 

 form volatile compounds, which may be conveniently compared with 

 the chloride and ethide of hydrogen. Now it is found that the 

 several proportions of metal or hydrogen contained in equal volumes 

 of these gaseous chlorides or ethides, are their respective atomic pro- 

 portions ; so that equal volumes of chloride or ethide of hydrogen, 

 zinc, arsenic, tin, mercury, lead, and bismuth, for instance, contain 

 1, 65, 75, 118, 200, 207,and 210 parts of hydrogen or metal respec- 

 tively. Hence the molecule of chloride of hydrogen, HC1, being 

 conventionally regarded as constituting two volumes, the atomic pro- 

 portion of a metal may be defined to be that quantity of the metal 

 which is contained in two volumes of its gaseous chloride, or bro- 

 mide, or ethide, or methide, &c. 



These two definitions having reference respectively to the specific 

 heats of the metals, and the molecular volumes of their gaseous com- 

 pounds, lead in all cases to the same conclusion. Thus 200 parts of 

 mercury is the quantity of mercury which has the same specific heat 

 as 108 parts of silver, and is also the quantity of mercury contained 

 in two volumes of mercuric chloride, mercuric ethide, &c. 



