M. Dumas on the Equivalents. 215 



8 Oxygen. 



8 + 8 = 16 .... Sulphur. 



8 + 32=40 . . . . Selenium. 



8 + 56 = 64 . . . . Tellurium. 



This difference of 8 or a multiple is shown in the group mag- 

 nesium, calcium, strontium, barium, and lead : the general for- 

 mula of the group is — 



Lithium, sodium, and potassium belong to another series, with 

 a difference of 16, a, a + d, a + 2d. 



7 Lithium. 



7 + 16 = 23 . . . Sodium. 

 7 + 32 = 39 . . . Potassium. 



Dumas has redetermined the atomic weight of tin, having 

 employed Berzelius's method. Pure tin, expressly prepared from 

 chloride of tin, was treated in a long-necked glass globe of the 

 hardest glass with nitric acid. The residual oxide was then 

 heated to redness in the flask for an hour. The experiment was 

 made with every precaution, and the number was found to be 

 58"8; but the oxide was still found to contain traces of water, 

 which was driven off by being heated in a platinum crucible. 

 The correction for this raised the equivalent to 59. 



The equivalents of titanium, tin, and tantalum form a series 



25 59 92, 



which has the difference 34. This difference also obtains be- 

 tween chromium and uranium, which have the equivalents 26 

 and 60. Chromium, molybdenum, vanadium, and tungsten 

 form also a series in which the difference is 22, — 



26 48 70 92 



These considerations lead to the confirmation of Prout's view, 

 that the equivalents arc multiples by whole numbers of a certain 

 basis, — with the modification, however, that for certain elements 

 this basis is not the eejuivalent of hydrogen, but probably 0-5. 



