370 On the Alloi^s o/S/eel. 



ofsixla, &c., there is no action takes place between them. In 

 such cases it acts just like steel; and no agent that we have as 

 vet tried, has produced voltaic action that was not first able to 

 set a portion of the platina free by dissolving out tlie iron. 



Other interesting phenomena exhibiteil by the action of acid 

 on these steels, arc the differences produced vvhen they are 

 hard and when soft. Mr. Daniel, in his interesting papei' 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 surface was 

 examined, it was covered with small cavities like v,orm-eaten 

 wood, and was comj)act 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 liard 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 fi- 

 brous; but the soft piece, on examination, is found to be coveretl 

 with a thick coat of grey metallic plumbaginous matter, soft 

 to the touch, and which may be cut with a knife, and its quan- 

 tity seven or eight times that of the powder on the hard piece : 

 it does not appear as if it contained any free charcoal, but con- 

 siderably resembles the plumbaginous powder Mr, Daniel de- 

 scribes as obtained by the action of acid on cast iron. 



The same difference is observed if pure steel be used, but it 

 is not so striking ; because, being much less rapidly attacked 

 by the acid, it has to remain longer in it, and the powder pro- 

 duced is still further acted on. 



The powder procured Irom the soft steel or alloy in these 

 experiments, when it has not remained long in the acid, ex- 

 actly resembles finely divided plumbago, and aj^pears to be a 

 carburet of iron, and probably of the alloying metal also. It 

 is not acted on by water, but in the air the iron oxidates and 

 discolours the substance. When it remains long in the acid, 

 or is boiled in it, it is reduced to the same state as the jiowder 

 from the hard steel or alloy. 



When any of these residua are boiled in diluted sulphuric 

 or muriatic acid, pi'otoxide of iron is dissolved, and a black 

 powder remains unalterable by the further action ol' the acid ; 

 it is apparently in greater (juantity from the alloys than from 

 pure steel, and when washed, dried, and heated lo 300° or 400^ 

 iu the air, burns like pvrophorus, with luucli iiimc : or if light- 

 ed. 



