282 THE CHEMISTRY OF THE SUN. [CHAP. 



atomic weight as referred to hydrogen shall be represented by 

 the same values. 



Unfortunately, however, in the case of most of the elementary 

 bodies which exist generally in the solid state, the determination 

 of vapour densities is either very difficult or impossible, so that 

 in addition to those we have named the facts have only been 

 ascertained in the case of cadmium, mercury, phosphorus, 

 arsenic, and sulphur, and all these are " anomalous/' that is, a 

 "law" founded on six cases fails in the next five tried. 



In the first four of these we have two distinctly opposed 



results 



Vapour density. Atomic weight. 

 Cadmium 56 112 



Mercury 100 200 



Phosphorus 62 31 



Arsenic 150 75 



That is to say, we have cases in which the density is half, others 

 in which it is double, the atomic weight. 



To bring out the facts in the preceding table, a very concrete 

 illustration may be pardoned. Suppose the complexity of the 

 bodies in the solid state to be represented by something higher 

 than a penny, the pennies being changed into halfpennies, or 

 even into farthings, by various dissociating agencies. Next, let 

 us assume that the molecular fineness produced by chemical 

 action and represented by the weighed atom in each case is 

 represented by a halfpenny. In the case of cadmium and 

 mercury the temperature needed to produce the vapour has 

 done more than chemical action, we get farthings. In the case 

 of phosphorus and arsenic temperature does less, and we get 

 pennies. Now as a matter of fact cadmium and mercury 

 are sluggish chemically, while phosphorus and arsenic 

 are active. 



The interesting point about these determinations is that 

 where there is chemical confusion there is also spectroscopic 



