80 



The experiments of Professor Graham in 1867, and more 

 recently those of Mr. Parry, show that hydrogen, carbonic 

 oxide and carbonic acid, and nitrogen are evolved from 

 wrought iron, cast iron, and steel, when heated in vacuo. 

 Therefore it seems probable that a part of the hydrogen 

 produced by the action of the acid on the iron may be 

 absorbed by th^ iron, its nascent state facilitating this. 

 And when the iron is heated by the effort of breaking it, 

 the gas may bubble up through the moisture on the frac- 

 ture. 



In Mr. Parry's experiments while one vol. of iron evolved 

 two vols, of gas when heated strongly in vacuo ; one vol. of 

 mild steel evolved only '13 of a vol. of gas. If from a small 

 evolution of gas during heating of steel in vacuo we may 

 argue a very small evolution of gas in steel soaked in acid, 

 then we are led to suppose that the bubbles evolved from 

 the hot moist fracture of a piece of steel will be very small 

 or imperceptible, which experiments amply confirm. 



