[ 194 ] 



XXV. The Periodic Law, and the Occurrence of the Elements 

 in Nature. By Thomas Carnelley, JD.Sc. {London), Pro- 



fessor of Chemistry in University College, Dundee*. 



§ 1. ~DUT few attempts have been made to account for the 

 -D present occurrence of the elements in nature, and 

 these may be briefly summed up in the statement generally 

 found in text-books, that some elements, such as gold, pla- 

 tinum, iridium, osmium, &c, always occur in the free state ; 

 others, such as mercury, silver, oxygen, nitrogen, &c, are 

 frequently found in this condition ; others, such as lead, tin, 

 &c, rarely so ; whilst elements such as fluorine, chlorine, 

 sodium, potassium, &c._, are never found but in a state of com- 

 bination. And, further, that metals occur, as a rule, most 

 commonly in the form of oxides, sulphides, carbonates, and 

 sulphates. 



§ 2. The most interesting of such attempts is that proposed 

 by Dr. Gladstone (Phil. Mag. [5] iv. p. 379). This, however, 

 deals rather with the degree of distribution of the elements in 

 nature than with the form in which they occur. In the paper 

 referred to, Dr. Gladstone divides the elements into four 

 classes : — (1) Plentiful, (2) Common, (3) Rare, (4) Very 

 Rare ; and he shows that the average vapour-density of the 

 first class is less than that of the second, and the latter less 

 than that of the third, and this last less than that of the fourth 

 class. From which he concludes that those elements having 

 the least vapour-density tended to remain more towards the 

 surface during the period of the earth's formation, whilst 

 elements having a high vapour-density accumulated more 

 towards the centre, and hence occur but rarely on the surface. 



MendeljefF (Zeitschr.f Chem. 1869, v. p. 405) has also 

 pointed out that all those elements which are found in greatest 

 quantity on the earth's surface have small atomic weights. 

 The converse of this, however, does not appear to be true; for 

 lithium, beryllium, and boron are far from occurring in large 

 quantities. 



§ 3. The theory proposed in the present paper, on the other 

 hand, deals rather with the occurrence than with the distribution 

 of the elements in nature. It has for its basis the Periodic Law 

 of the chemical elements, first enunciated by Newlands as the 

 Law of Octaves, and subsequently and independently deve- 

 loped by MendeljefF and Lothar Meyer. 



The following is a Table of the Natural Classification of the 

 Elements in the form adopted by MendeljefF. This table is 



* Communicated by the Author. 



