ZINC, CADMIUM, LEAD, &c. 



a formidable obstacle to the rigid determination 

 of their atomic weights. 



Deter- 1. Fourcroy, long ago, stated, that the pro- 



toxide of mercury is a compound of 100 metal 



and 4 oxygen ; but, from the loose way in which 

 this chemist was accustomed to express himself, 

 we can consider this determination in no other 

 light but that of a fortunate conjecture. Mr. 

 Donovan, Donovan, from a number of experiments on both 

 oxides, has concluded that protoxide of mercury 

 is Composed of 



Mercury . 100 or 2 4-2 71 



Oxygen . 4-12 - I* 



And peroxide of 



Mercury 100 or 25-575 



Oxygen . 7'82 - 2 



The atomic weight of mercury, deduced from 

 these two oxides, not being exactly the same, it 

 is obvious that the experiments from which the 

 constitution of these oxides has been deduced, 

 are not quite exact. The mean of both gives us 

 24 '923 for the atomic weight, which differs less 

 than ^joth from 25, the atomic weight of mer- 

 cury, deduced from the composition of protoxide 

 of mercury, as stated by Fourcroy. 



M. Sefstrom made a set of experiments in Ber- 



and Sef- 

 strom. 



* Annals of Philosophy, XIV. 



