316 THE SCIENTIFIC PAPERS OF 



hard steel, spring steel, and so forth, and to call "steel" all 

 malleable iron which had passed through the fluid condition. 

 This definition would exclude, however, natural, blister, and 

 puddled steel, and was therefore in his opinion inadmissible. On 

 the other hand, Dr. Siemens considered it would be difficult, if 

 not impossible, to define steel by its mechanical qualities. Steel 

 was almost the hardest substance in nature, if treated in a certain 

 way ; treated in another way it was the most elastic of metals, if 

 not the most elastic substance in nature ; and treated in another 

 way it was nearly the most ductile of metals. It was decidedly 

 the strongest substance in nature. Dr. Percy had said he con- 

 sidered steel a metal in which iron was the chief constituent, and 

 which would harden. If that definition were adopted, a limit 

 would be arrived at where it would be uncertain whether a sub- 

 stance was steel or iron. One rail delivered by a manufacturer 

 would come under the definition of steel, and another rail delivered 

 in the same contract would come under the definition of iron, 

 simply because one had rather less carbon than the other ; and 

 after all, the mildest steel, and iron itself, would admit of 

 tempering. Dr. Percy had said that molten iron, according to 

 Mr. Hackney's definition, ought to be called steel ; but it had 

 been already remarked that such iron could not be treated 

 mechanically ; it would not stand rolling and hammering, and 

 therefore it was not steel. He thought, however, a definition 

 might be found which would answer all requirements, namely, 

 that steel was a compound of iron with any other substance which 

 tended to give it superior strength. This definition would embrace 

 the different kinds of steel, from the hardest tool steel down to the 

 mildest, and would embrace those compounds in which manganese, 

 tungsten, chromium, phosphorus, or sulphur, replaced the carbon 

 of ordinary steel. It had been objected that steel was uncertain 

 in its nature ; that it sometimes was very ductile and very strong, 

 and at other times would break short and was not be trusted. 

 Mr. Walker had said that, on that account, he preferred iron to 

 steel for structural purposes. Steel was a material of a much 

 higher nature than iron. It was much stronger, and could be 

 made to possess nearly any degree of strength, hardness, and 

 ductility, between wide limits, that it was desired to give it ; but 

 it was only natural that such a material should require greater 



