THE CHEMISTRY OF THE ROCKS. 



701 



We have also further assumed that the elements, in their gaseous 

 states, have specific gravities corresponding to their atomic weights. 

 It is well known that all gases, whether simple or compound, at the 

 same temperature and pressure, and not near to a condensing point or 

 other change of state, contain precisely the same number of molecules 

 in the same volume. Therefore, it necessarily results that the same 

 measures of the different gases should have weights corresponding to 

 the weights of the molecules of which they are composed. Thus the 

 atom of oxygen is sixteen times as heavy as that of hydrogen ; there- 

 fore a cubic foot of oxygen gas will weigh sixteen times as much as a 

 cubic foot of hydrogen gas. This is found to be experimentally true 

 of all the gases that can be measured and weighed. The apparent 

 but not real exceptions are that in arsenic and phosphorus two atoms 

 of the element unite to form one molecule of the gas, thus making it 

 twice as heavy as it would be, according to the general rule ; while, 

 in the case of mercury and cadmium, the atom divides into two in 

 forming their vapors. Hence we are not absolutely sure in regard to 

 the vapor-molecule, and therefore vapor-density, of such elements as 

 carbon, silicon, and calcium, which chemists have not been able to 

 volatilize. But there is every probability, both from analogy and the 

 position in which some of them are found in the photosphere of the sun, 

 that the vapors of nearly all of them correspond strictly to their com- 

 bining numbers. The following table, therefore, will show the relative 

 positions, in the atmospheric strata, of some of the most important 

 elements, with the weights of their atoms in hydrogen units, their va- 

 por-densities, compared with air, and the solid specific gravities of 

 some of them as compared with water : 



GASES. 



Atomic Weights. 

 H = 1. 



Sp. gr. of Gas. 

 H= 1. 



Sp. gr. of Solid. 

 Water = 1. 





1 



12 

 14 



16 

 23 

 24 



27.5 



28.5 



32 



35.5 



39 



40 



56 



63.5 



200-5-2 



108 



196.5 



198 



.069 

 .828 

 .972 

 1.105 

 1.59 

 1.66 

 1.90 

 1.97 

 2.22 

 2.44 

 2.69 

 2.76 

 3.86 

 4.39 

 6.97 

 7.47 

 13.57 

 13.66 



2!09 



* *98 

 1.74 

 2.60 

 2.40 

 2. 



1.33 



.86 



1.58 



7.80 



8.96 



13.60 



10.53 



19.34 



21.50 





Sodium 



Magnesium 



Aluminum 



Silicon 



Sulphur 



Chlorine 



Potassium 



Calcium 



Iron 



Mercury 



Gold 



Platinum 





It will be noticed from this table that the elements were arranged 

 in positions most suitable for their combination and deposition, both 

 in the geological order, and in the probable order of their condensa- 



