348 Dr. Thomson's Observations on the Weights of [Not. 



Weight of an atom. 



74 Peroxide of platinum 25*625 



75 Palladium 7-000 ' 



76 Oxide of palladium 8-000 



77 Rhodium 15-000 k 



78 Protoxide of rhodium 16-000 



79 Deutoxide of rhodium 17-000 



80 Peroxide of rhodium 18-000 



81 Iridium 6-000 l • 



82 Antimony 5*625 m 



100 grains of this oxide, when heated to redness, give off 12-^ 

 cubic inches of oxygen gas, and are reduced to the metallic 

 state. Hence protoxide of platinum is a compound of 100 metal 

 4- 4*423 oxygen. Hence the number for platinum and pi-otoxide 

 of platinum. The number for the peroxide is rather conjectural. 

 The experiments of Berzelius and Edmond Davy on the oxides 

 and other compounds of platinum do not agree with each other. 



• The weight of palladium and its oxide is founded on the 

 experiments of Berzelius. He found the oxide a compound of 

 100 metal + 14*209. The number 7 supposes the oxide a 

 compound of 100 metal + 14*285 oxygen, which does not mate- 

 rially differ from the result obtained by Berzelius. 



k The weight of rhodium and its three oxides are deduced 

 from the experiments of Berzelius ; but I do not think that much 

 confidence can be put in their accuracy, they were made upon 

 so small a scale. He makes the composition of the three oxides 

 as follows : 



Oxygen. 



Protoxide 100 metal + 6*71 or 1 atom 



Deutoxide 100 metal + 13-42 . . 2 atoms 



Peroxide 100 metal + 20-13 . . 3 atoms 



1 According to Vauquelin, sulphuret of iridium is a compound 

 of 3 metal + 1 sulphur. This gives the weight of an atom of 

 iridium 6, if the sulphuret be composed of 1 atom metal + 

 1 atom sulphur. 



m I have deduced this number from a very careful analysis 

 which I made of sulphuret of antimony ; I found it composed of 

 100 antimony + 35*572 sulphur. Now 35*572 : 100. :: 2 : 5-625. 

 The protoxide of course must be 6-625. This agrees nearly, 

 though not quite, with Berzelius's analysis. According to him, 

 protoxide of antimony is a compound of 100 metal + 18-6 

 oxygen. According to the number which I have adopted, it is 

 composed of 100 metal + 17*775 oxygen. The peroxide has 

 never been analyzed ; but there is reason to believe that it con- 

 tains twice as much oxygen as the protoxide. The deutoxide is 



