GASEOUS BODIES. 



to hesitate about extending the same law to 

 these bodies also. 



Thus it appears, that the atomic weight of 

 oxygen is obtained by dividing the specific gra- 

 vity of oxygen gas by itself j for ^4 = 1 ; but 

 the atomic weights of the other gases and vapours 

 are obtained by dividing the specific gravity of 

 the gas or vapour by half the specific gravity of 

 oxygen gas, or 0*5555.* 



The specific gravities of oxygen gas, hydrogen 

 gas, chlorine gas, and azotic gas, have been de- 

 termined with rigid accuracy in the preceding 

 chapters. The knowledge of the atomic weights 

 of the other bodies will enable us to determine 

 the specific gravities of the vapours and gases 

 of which they constitute parts, with equal ac- 

 curacy ; for we obtain these specific gravities by 

 multiplying the atomic weights by O5555. 



The following table exhibits the atomic weights 



* I need hardly point out to the reader, that the reason why the multi- 

 plicand of the specific gravity of the gases is ^, or ^th the specific gravity of 

 oxygen gas, instead of simply ^ and ^th, is, that the specific gravities and 

 the atomic weights are referred to different standards. The specific gravity 

 of atmospheric air is reckoned unity, and that of every other gas is referred 

 to it ; but the atomic weight of oxygen being unity, and. that of all the 

 other gases referred to it, as far as atomic weights are concerned, it is ob- 

 vious, that when specific gravities are to be converted into atomic weights, 

 we must employ for our divisor half or |th the specific of oxygen gas, in 

 order to change one system into the other. All this trouble would be 

 saved, if we were to make the specific gravity of oxygen gas unity, as well 

 as its atomic weight. 



0,2 



