264, Mr. Stodart and Mr. Faraday 
placed in saline solutions, as muriate of soda, &c., there is no 
action takes place between them. In such cases it acts just 
like steel ; and no agent that we have as yet tried, has pro- 
duced voltaic action that was not first able to set a portion of 
the platina free by dissolving out the iron. 
Other interesting phenomena exhibited by the action of 
acid on these steels, are the differences produced when they 
are hard and when soft. Mr. Daniel, in his interesting paper 
on the mechanical structure of iron, published in the Journal 
of Science, has remarked, that pieces of hard and soft steel 
being placed in muriatic acid, the first required five fold the 
time of the latter to saturate the acid ; and that when its sur- 
face was examined, it was covered with small cavities like 
worm-eaten wood, and was compact and not at all striated, 
and that the latter presented a fibrous and wavy texture. 
The properties of the platina alloy have enabled us to ob- 
serve other differences between hard and soft steel equally 
striking. When two portions of the platina alloy, one hard 
and one soft, are put into the same diluted sulphuric acid and 
suffered to remain for a few hours, then taken out and ex- 
amined, the hard piece presents a covering of a metallic 
black carbonaceous powder, and the surface is generally 
slightly fibrous, but the soft piece, on examination, is found to 
be covered with a thick coat of grey metallic plumbaginous 
matter, soft to the touch, and which may be cut with a knife, 
and its quantity seven or eight times that of the powder on 
the hard piece : it does not appear as if it contained any free 
charcoal, but considerably resembles the plumbaginous pow- 
der Mr. Daniel describes as obtained by the action of acid 
on cast iron. 
