EVOLUTION OF THE CHEMICAL ELEMENTS. 535 



under extremely low temperature. And it may be supposed that dur- 

 ing this period other gases may exist associated with these, which, 

 however, unlike them, are unable to sustain the successively higher 

 and higher temperatures which the nebula acquires in its process of 

 condensation and organization into a system, and at certain stages of 

 this process are dissociated and resolved into aggregates of a different 

 constitution, suited to these temperatures. Some of these latter new 

 aggregates would naturally assume the liquid and solid forms at tem- 

 peratures still high as compared with those to which we are accus- 

 tomed, and constitute in the cooled-oflf crust of the planets the various 

 metals and metalloids. In this manner we should have no difficulty 

 in accounting for the existence of all the elements found on the earth, 

 even if it were positively known that only the lighter gases were 

 present in the parent nebulae. 



The recognized elementary substances, presenting so many dijffer- 

 ent qualities, vary greatly in their so-called " atomic weights." This 

 means simply that their molecules vary greatly in mass. The hydro- 

 gen molecule is the least known, and is therefore taken as the stand- 

 ard. Compared with this as unity, we find that the molecule of oxy- 

 gen contains 16 times as much matter, that of carbon contains 12, that 

 of nitrogen 14, and that of chlorine 35| times as much. But these, 

 instead of representing large equivalents, are, when compared with 

 most of the metals, very small. One molecule of mercury contains 

 two hundred times as much matter as one of hydrogen. The atomic 

 weight of gold is 197, of platinum 197*4, of lead 207, and of bismuth 

 208 ; while the thorium equivalent, which was quadrupled in the new 

 system, is now put at 231-4, being the largest of all the elementary 

 units. Whether hydrogen, carbon, nitrogen, oxygen, or any of the 

 other abundant elements having small molecules have entered into the 

 composition of these heavy substances, is a legitimate question. The 

 fact that these molecules are stable, whether combined or uncombined, 

 is favorable to this view, although there may exist, as component units 

 of the molecules of the metals, many equally stable aggregates which 

 no human power can dissociate from their present combinations. But, 

 if known elements were employed as components of other known ele- 

 ments having larger molecules, the very fact that they are elements, 

 i. e., that we are unable to decompose them, would render it impos- 

 sible to know that such was the case. Think how many hydrogen, 

 nitrogen, or oxygen molecules might enter into the system that consti- 

 tutes the unit of bismuth or of gold ! 



Now, it is a remarkable fact that those elements which have very 

 high condensing points, i. e., which assume the liquid (or solid) form 

 at very high temperatures, generally have large combining numbers, 

 that is, large molecules; while those having low condensing points and 

 which are gaseous at ordinary temperatures, as a rule have small com- 

 bining numbers, or small molecules. To this, carbon on the one hand, 



