50 PRINCIPLES OF CHEMISTRY. 



found to weigh 71 grammes, then the atomic weight of the latter 

 element must be 35.5, because 2 and 71 represent the relative weights 

 of the molecules of the two elements. Each molecule being com- 

 posed of 2 atoms, these molecular weights have to be divided by 2 in 

 order to find the atomic weights, which are, consequently, 1 and 35.5 

 respectively. 



In comparing by this method oxygen with hydrogen, it is found 

 that equal volumes of these gases weigh 32 and 2 respectively, that 

 the atomic weight of oxygen is consequently 16, and not 8, as deter- 

 mined by chemical methods. 



This mode of determining atomic weights may be applied to all 

 elements which are gases or which may without decomposition be 

 converted into gas. 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 

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

 of its volatile compounds, and these 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 spe- 

 cific 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 be thus expressed : Atomic weighl 

 are inversely proportional to the specific heats; or the product of the ! 

 atomic weight multiplied by the specific heat is a constant quantity^ 

 for the elements examined. 



Elements. Specific heats. Atomic weights. Product of specific heat 



( Water = 1.) X atomic weight. 



Lithium, 09408 7 6.59 



Sodium, 0.2934 23 6.75 



Sulphur, 02026 32 648 



Zinc, 00956 65 6.22 



Bromine (solid), 0.0843 80 6 75 



Silver, 0.0570 108 6.16 



Bismuth, 0.0308 209 644 



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 varia- 



