110 
3rd. The surface action of hydrochloric acid was rather 
more marked than with nitric acid, and seemed to develope 
fibrous markings, while the nitric acid only fretted the surface. 
The hardened steel was very little eaten away indeed, 
while the mild steel was half eaten away, the action being 
irregular and much more marked in some places than in 
others. The action on the charcoal was intermediate 
between the mild and hardened steel. 
On moistening the fracture of the charcoal iron bubbles 
were given off in great abundance from the whole surface 
of the fracture. On trying the same experiment with the 
part adjacent, but not actually immersed in the acid, a few 
small bubbles were seen to rise from the surface of the 
fracture, even at a distance of I7c.m. from the surface of the 
liquid. These bubbles were found to increase in number 
and the toughness to decrease as you approached the surface 
of the acid. Moreover, when that part of the wire not 
immersed in the acid was broken, the bubbles arose almost 
exclusively from the centre of the fracture ; while from the 
part immersed in the acid they arose from the whole surface, 
and took less time to attain their maximum. 
No bubbles were visible to the unaided eye on the 
moistened fracture of the mild steel or on the hardened 
steel. That part of the mild steel immersed in the acid 
broke when bent like a pipe stem, 1 centimetre above the 
surface of the acid it was a little tougher, and at 2 centimetres 
distance it was as tough as before immersion, and would 
stand bending to and fro many times before breaking. 
The hardened steel, immersed in acid broke very short, 
but a little tougher than the mild steel ; perhaps because it 
was not so much eaten away. At 1 centimetre above the 
surface of the acid it broke less short than in the acid, and the 
toughness seemed to increase with the distance from the 
acid until at 4 centimetres it broke as tough as before 
immersion. 
