BEHAVIOUR OF IRON IN CONTACT WITH SULPHURIC ACID. 397 
ments with wrought iron and 967% sulphuric acid (pure for 
analysis). 
If the word ‘‘ passive’’ be here used as denoting ‘‘ inac- 
tive,’’ then there is no great objection to it, for the activity 
in the case of action on wrought iron and cast iron is 
excessively slight. But the word “ passive’ could not at 
any rate be applied to iron in pure sulphuric acid as denoting 
a State in any sense similar to that of the state of iron when 
placed in 1°4 sp. gr. nitric acid. The results of the follow- 
ing experiments bring out the difference between the two 
cases. 
J.—I a. When passive iron, lying in 1°2 nitric acid was 
touched with platinum, neither iron, nor the platinum 
experienced any change noticeable to the eye. 
Is. When iron lying in concentrated sulphuric acid (967) 
was touched with platinum, then although there might. 
have previously been no bubbles of gas coming from 
the iron, bubbles of gas appeared after contact almost. 
immediately on the platinum. 
II.—II a. The cell. Passive iron [1°2 nitric acid] Platinum 
was found to have a potential of 0°13 to 0°3 volt, while 
the cell Active Iron [1°2 nitric acid] Platinum had a. 
potential of 0°95 to 1°1 volts. In both cases the iron 
was positive to the platinum. 
When passive iron immersed in 1°2 nitric acid was touched 
with tin or copper, the iron became suddenly active, and 
the. potential immediately rose to that of the second cell, 
viz., 1°1 volts. When the passive iron was lifted into the 
air fora few moments and replaced in the solution, there 
was no considerable influence on the potential of the cell. 
Ifs. The E.M.F. of the cell. Iron [concentrated sul- 
phuric acid] Platinum was found to be much more 
variable than the H.M.F. of the cell where iron, passive 
