DETERMINATION OF ATOMIC WEIGHTS. 49 



tively, that the atomic weight of oxygen is consequently 16, and 

 not 8, as determined by chemical methods. 



This mode of determining atomic weights may be applied to 

 all elements which are gases or which may be converted into 

 them. There are, however, elements which cannot be volatilized, 

 and in this case it becomes necessary to determine the specific 

 gravity of some gaseous compound of the element. The ele- 

 ment carbon itself has never been volatilized, but we know many 

 of its volatile compounds, which may be used in the determina- 

 tion of its atomic weight. 



Determination of atomic weights by specific heat. Specific heat 

 has been stated to be the quantity of heat required to raise the 

 temperature of a given weight of any substance a given number 

 of degrees, as compared with the quantity of heat required to 

 raise the temperature of the same weight of water the same 

 number of degrees. 



In comparing atomic weights with the numbers expressing 

 the specific heats, it is found that the higher the atomic weight 

 the lower the specific heat, and the lower the atomic weight the 

 higher the specific heat. This simple relation may thus be ex- 

 pressed : Atomic weights are inversely proportional to the spe- 

 cific heats ; or, the product of the atomic weight multiplied by 

 the specific heat is a constant quantity for the elements ex- 

 amined. 



Elements. Specific heats. Atomic weights. Product of specific 

 (Water=l.) heat X atomic weight. 



Lithium, 0.9408 7 6.59 



Sodium, 0.2934 23 6.75 



Sulphur, 0.2026 32 6.48 



Zinc, 0.0956 65.2 6.24 



Bromine (solid), 0.0843 80 6.75 



Silver, 0.0570 108 6.16 



Bismuth, 0.0308 210 6.48 



An examination of this table will show this relation between 

 atomic weight and specific heat, and also that the product of 

 atomic weight multiplied by specific heat is equal to about 6.5. 

 The variations noticed in this constant quantity of about 6.5 

 may be due to errors made in the determinations of the specific 



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