IRON. 347 



The 8 grains of sulphurous acid fly off in the 

 state of gas, and the 2 grains of oxygen unite 

 with the 18 grains of protoxide of iron, and con- 

 vert them into 20 grains of peroxide. The re- 

 maining J grains of sulphuric acid, united to the 

 atom of water, are driven off in the state of fum- 

 ing sulphuric acid, and weighing 11 '125 grains. 



From this statement it is obvious, that when 

 17*375 grains of protosulphate of iron are thus 

 treated, 7*59375 grains of water (or 7 atoms 

 th atom) will be driven off; 2| grains of sul- 

 phuric acid will be converted into 2 grains of 

 sulphurous acid (which will fly off) and half a 

 grain of oxygen, which will convert the 44 grains 

 of protoxide into 5 grains of peroxide. The 

 remaining 2 grains of sulphuric acid united 

 with 0*28125 grains of water, (the ith atom still 

 remaining) will be driven off in the state of 

 fuming sulphuric acid. 



From the preceding exposition it is plain, that 

 after all the water has been driven off, which 

 can be made to leave 17*375 grains of protosul- 

 phate of iron by a moderate heat, one fourth of 

 an atom, or 0*28125 grain still remains. Hence, 

 the whole water of crystallization amounts to 

 7*6 + 0*28125 = 7-88125 grains. This comes 

 so near 7*875 grains, which is the equivalent of 

 7 atoms, that there can be no doubt that 7 atoms 

 is the true quantity of water present. The small 

 excess (only 0*00625 grain) was owing to a com- 



16 



