400 C. E. FAWSITT AND A. A. PAIN. 
The rather sudden increase in velocity of action which 
we have observed in proceedings from 85% to 80% and from 
70% to 64°5/ acid, may not be unconnected with the fact 
that the monohydrate, H.SO., H.O contains 845% of 
H.SO, while the trihydrate H.SO,, 3 H,O contains 64°77 
H,SO,. * 
The amount of action depends to some extent on whether 
the acid is kept in movement or is left undisturbed in con- 
tact with the iron. One set of experiments, Series A, was 
conducted without shaking, and the rate measured by 
reading the volume of gas (reduced to N.T.P.) evolved from 
the iron and acid contained ina flask. In Series B, the 
flasks containing the iron and acid were shaken, and the 
rate measured by noting the diminution in weight of the 
iron used. 
SERIES ‘°A.”’’ 
The iron used was a steel wire of the following com- 
position:—carbon 0°51%, phosphorus 0°046%, silicon 0°0837/, 
sulphur 0°058%, manganese 0°487%. The steel wire hada — 
diameter of 0°0706 centimetres. 
A length of 634 cm. of wire, weighing 20 grams, was 
polished with emery paper and was cut up into lengths of 
ocm. This lot of 20 grams weight was the amount used 
in each experiment, and the surface exposed to the acid 
was approximately 143 sq. cms. in each case, The volume 
of the acid used was 120 cc. This was put into a Jena 
distilling flask (130 cc.) with the portion of the neck above 
the side tube shortened so as to reduce the gas space in 
the flask toa minimum. The side tube was shaped to a 
delivery tube permitting the collection of evolved gas over 
mercury. After introducing the iron and acid, the neck of 
the flask was closed witha paraffined rubber stopper. This 
arrangement was proved to be gas-tight under a pressure 
of 24 cm. of mercury. The flasks were placed in a water 
