BEHAVIOUR OF IRON IN CONTACT WITH SULPHURIC ACID. 40] 
thermostat at 30° O., and the gas was collected in a 
measuring tube over mercury. 
Owing to it being necessary to displace a small and 
variable amount of mercury in the delivery tube before any 
readings of the volume could be made, it was necessary to 
wait for 1—8 days, before the first reading could be taken. 
When therefore no reading for the volume of gas is given 
in the first few days (Table II), this does not mean that no 
gas was evolved, but that it was not possible to register 
the volume with the method of collection which was 
adopted. Using 120 cc. of acid, there is not a very marked 
change in the concentration of the acid even in several 
weeks, for although acid is being used up by water it is also 
used up in order to form the compound FeSO,, H.O, which 
has been shown’ to be the compound formed in the action 
of concentrated sulphuric acid oniron. Fe+H,S0O,+H,O 
= FeSO,, H.O+ Ho. 
An extreme case is next given where the action is taken 
as much greater than anything actually experienced in 
these experiments. Taking 94/ acid as an example, and 
allowing this to act on steel for 45 days at 30°C., the 
Maximum amount of gas which could be produced in this 
time (30° O.) from 140 sq. cm. of the steel used, is say, 45 
x 24 x 3°D cc. = 3780 cc. This (maximum) amount of 
gas is calculated on the assumption that the velocity 
throughout was the maximum velocity ever obtained in an 
experiment with 94% acid at 30° CO. 
These 3°780 litres would use up 16°8 grams of sulphuric 
acid (H.SO.). 16°8 grams of acid and 3°93 grams of water 
are thus removed. Now the original acid had a volume of 
120 cc. and weighed 217°4 grams; this contains 205°8 grams 
H.SO, and 11°6 grams water. After 45 days action 189 
grams acid and 7°7 grams water are left, so that the per- 
+ Powell, Proc. Roy. Soc. N.S.W., xuvii, 59, 1913. 
Z—September 4, 1918. 
