346 Dr. Thomsons Observations on the Weights of [Nov. 



Weight of an atom. 



47 Peroxide of uranium 34*250 



48 Cerium 5-750 



49 Protoxide of cerium . 6*750 * 



50 Peroxide of cerium 14*500 



51 Zinc 4*125 



52 Oxide of zinc 5*125 k 



53 Lead 13*000 



54 Protoxide of lead 14*000 c 



protoxide of uranium is a compound of 100 metal + 6*373 

 oxygen. This would make the weight of an atom of uranium 

 15*691. I take 15*625 as the nearest multiple of *125. Schoii- 

 bert has shown that the peroxide contains 14- times as much 

 oxygen as the protoxide. It must, therefore, be a compound of 



2 atoms metal + 3 atoms oxygen, and its weight must be as in 

 the table. 



a The numbers for cerium and its oxides are derived from the 

 experiments of Hisinger. From his analysis of the salts of 

 cerium, it is probable that the protoxide is composed of 



Cerium 100*00 



Oxygen 17*41 



and the peroxide of 



Cerium 100*000 



Oxygen 26*115 



Now if we suppose the protoxide a compound of 1 atom metal 

 + 1 atom oxygen, and the peroxide of 2 atoms metal + 



3 atoms oxygen, we obtain the numbers in the table. 



b Zinc combines with only one dose of oxygen. Berzelius and 

 Gay-Lussac found the oxide composed of 100 metal + 24*4 oxy- 

 gen ; while I obtained 100 metal -f 24*16 oxygen. According 

 to the first of these results, an atom of zinc weighs 4*098 ; 

 according to the second, 4*139. The mean of both gives 4*118. 

 Now 4*125 (which I prefer, because it is a multiple of -125) 

 differs very little indeed from this number. 



. ., Oxide 



Acid, c , . 



of lead. 



c Berzelius found sulphate of lead com-^ oa-rto i 7Q.fi« 

 posed of 5 



Now 26*32 : 73*68 :: 5 : 13*996 ; a number which approaches so 

 near 14 that there can be little hesitation in pitching upon 14 as 

 the true number. Of course the number for lead must be 13. 

 Berzelius has shown that peroxide of lead contains twice as 

 much oxygen as protoxide. Hence it must weigh 15. I consider 

 red had as a compound of protoxide and peroxide. 

 2 



