VOLUMES OF ATOMS IN THE GASEOUS STATE. l.r> 



From these tables, it appears that a simple relation always 

 subsists between the combining measures of different bodies in 

 the gaseous state : 



That the combining measure of a few bodies is the same as 

 that of oxygen, or one volume ; of a large number, double that 

 of oxygen, or two volumes ; and of a still larger number, four 

 times that of oxygen, or four volumes; while combining mea- 

 sures of other numbers of volumes, such as three and six, or 

 of fractional portions of one volume, such as one-third, are 

 comparatively rare ; 



That the specific gravity of a gas may be calculated from its 

 atomic weight, or the atomic weight from the specific gra- 

 vity, as they are necessarily related to each other. Thus, to 

 find the specific gravity of a vapour like that of phosphorus, 

 of which the combining measure is one volume, or the same 

 as that of oxygen. The specific gravities of two bodies, of which 

 the volumes of the atoms are the same, must obviously be as 

 the wdyhts of these atoms. Hence, 100 and 392.28 being 

 the atomic weights of oxygen and phosphorus, and 1 102.6, 

 the known specific gravity of oxygen, the specific gravity of 

 phosphorus vapour is obtained by the following proportion 



100 : 392.28 : : 1102.6 : 4323.7 

 =sp. gr. of phosphorus vapour. 



Secondly, to find the specific gravity of a vapour like that 

 of fluorine, of which the combining measure may be presumed 

 to be two, or double that of oxygen. The atomic weight of 

 fluorine being 233.8, 



]00 : 233.8 : : 1102.6 : 2584 = 



twice the specific gravity of fluorine, being the weight of two 

 volumes, and the specific gravity required is 1292. 



These cases are examples of a general rule, that the specific 

 gravity of a body in the state of vapour is obtained by multi- 

 plying the atomic weight of the body by 1102.6, the specific 

 gravity of oxygen, and dividing by 100. The number thus 

 found must then be divided by the number of volumes which 

 are known to compose the combining measure of the vapour. 



The specific gravities thus calculated are generally more 

 accurate than those obtained by direct experiment, from the 

 circumstance that the operation of taking the specific gravity 

 of a gas is generally less susceptible of precision, than flic 

 chemical analyses on which the atomic weights arc founded. 



