BEHAVIOUR OF IRON IN CONTACT WITH SULPHURIC ACID. 405 
Comparing the 94% acid when shaken with the results 
obtained in Table II, we notice that °8605 gram of iron is 
lost in 28 days from 35 square centimetres of surface. This 
means that 340 cc. of hydrogen were produced by the 
solution of this °8605 gram of iron, or 1°4 cc. per hour per 
sq. decimetre. This is the average rate for the 28 days, 
and is just about equal to the rate (1°36) obtained from the 
undisturbed acid after 43 days. As the average rate for 
94% acid for 28 days in Series ‘‘A”’ (Table IT) is only 0°35 
cc. per sq. decimetre per hour, the accelerating effect of 
shaking is thus very noticeable. It is noticeable also in the 
other concentrations of sulphuric acid used. 
Conclusions.—(1) The solvent effect of sulphuric acid, of 
concentration (80% —94%) H.SO:, on steel is noticeably 
increased by shaking the vessel containing the acid and 
steel. 
(2) 97°4% H,SO, and 89°3 H.SO, have less action on the 
steel used than 947%, 90°9% , 87°9 % or 85% acid. 
(3) As the action of the acid on iron or steel produces a 
form of ferrous sulphate monohydrate (FeSO,, H,O) on the 
surface of the iron, this causes a slowing down of the action 
and prevents action almost entirely in some cases. 
(4) No real similarity exists between iron which is slowly 
dissolving in concentrated sulphuric acid and “‘ passive’’ 
iron as produced by dipping iron into 1°4 sp. gravity nitric 
acid. 
