M. C. Lea — Atomic Weights of the Elements. 387 



alongside of the other members of its group. It is, therefore, 

 omitted from the above table. Also in the paper just referred 

 to gold was placed amongst the elements having colored ions 

 only. The auric ion is certainly colored, but about the aurous 

 ion there is some doubt ; the oxids and the haloids are colored 

 but as they are insoluble they give no positive information. It 

 appears, however, that when aurous chloride is dissolved in 

 sodium chloride it yields a colorless solution from which color- 

 less crystals are obtained. Various other double salts form 

 both colorless solutions and colorless crystals. The following 

 are examples : Ammonium aurammonium sulphite, sodium 

 aurothiosulphate, potassium aurocyanide, etc.* 



As it seems characteristic of the soluble salts to be colorless, 

 I conclude that gold must be considered as having both colored 

 and colorless ions. It is, therefore, a transitional element and 

 finds its place in the above table where elements of that class 

 appear in italics. It is, however, interesting to observe that 

 just as these two metals cerium and gold are at the very limit- 

 ing point between two classes, so there are spaces open for 

 them in each of these classes, a circumstance that can hardly be 

 fortuitous. 



Table of Differences. 



If the respective numbers of the first column in the preced- 

 ing table be each subtracted from the corresponding number of 

 the second column, the second column from the third and so 

 on, we obtain a series of differences which are given in the 

 table below. 



18 16-5 44-5 47 



16 



16 



46 



47 



. - - - 







48 



49 









45 



49 









44 



88 













88 



_ _ _ 



_ 



45 



88 



15 



41-3 



46*7 



88 



16 



42 



45 



90 



16 



44 



46 



88 



17 



44 



45 



88 



16 



47 



46 





It has been remarked, I think as far back as the time of 

 Dumas that differences of 16 between the atomic weights fre- 

 quently presented themselves and occasionally differences of 

 forty-five or thereabouts. But these were scattered cases. In 

 the above table of differences all the elements are repre- 

 sented with the exception of the comparatively small group 

 having ions always colored. As has been already said, this 



* Roscoe and Schorlemmer, 1st ed., ii, 2, pp. 380-1. 



