348 IRON, NICKEL, COBALT, &c. 



mencement of decomposition, for the whole of 

 the salt thus treated was not soluble in water. 

 Thus it appears that 17*375 grains of protosul- 



phate of iron contain 







1 atom sulphuric acid = 5 

 # 7 atoms water . =7-375 



12-875 



Atom of The 4%5 grains, wanting to make up the whole 

 oflroni 17*375, are obviously protoxide of iron ; and, as 

 the salt is neutral, 4*5 must denote the atomic 

 weight of protoxide of iron. 



3. The preceding analysis of protosulphate of 

 iron is rigidly exact ; but it proceeds upon as- 

 sumptions which require to be proved. It will 

 now be requisite to state the experiments by 

 which I satisfied myself that 3%5 is the true ato- 

 mic weight of iron. 



Atomic 35 grains of pure iron were put into a small 

 iToJfalter- retort, with dilute sulphuric acid. A complete 

 solution took place ; and the volume of the hy- 

 drogen gas evolved (reduced to the mean tem- 

 perature and pressure) was 59 cubic inches. 

 Consequently, the iron must have combined with 

 a quantity of oxygen, which, had it been in the 

 gaseous state, would have amounted to -^, or 

 29*5 cubic inches, which weigh almost exactly 

 10 grains. From this it is obvious, that when 

 3'5 grains of pure iron are dissolved in dilute sul- 



