SCIENTIFIC NEWS. (J3 



Properties of blued Steel not generally known. 

 ' IN making fprin£s of fteel the metal is drawn or hammered Mcth ° d °f »**« 

 out and fafhioned to the defired figure. It is then hardened by 

 ignition to a low red heat and plunging it in water, which 

 renders it quite brittle. And laftly, it is tempered either by Hardening, 

 blazing or blueing. The operation of blazing confifts in ^^ gm m 

 freearing the article with oil or fat, and then heating it till 

 thick vapours are emitted and burn off with a blaze. I fup- 

 pofe this temperature to be nearly the fame as that of boiling 

 mercury, which is generally reckoned to be at the 600° of 

 Fahrenheit, though, for reafons I (hall in future mention, I 

 think this point requires to be examined. The operation of 

 blueing confifts in firft brightening the furface of the fteel, and 

 then expofing it to the regulated heat of a plate of metal or a 

 charcoal fire, or the flame of a lamp until the furface acquires 

 a blue colour by oxidation. The remarkable facls which I A blue fpring; 

 have here to prefent to the notice of philofophers are that Mr. brightening an<t 

 Stodart afTures me that he has found the fpring or elafticity of rcftored by blue- 

 the fteel to be greatly impaired by taking off the blue with 1 "* a§ain ' 

 fand paper or otherwife; and, what is (till more ftriking, that 

 it may be reftored again by the blueing procefs without any 

 previous hardening or other additional treatment. 



Mr. Hardy, who is meritoriouily known as a fkilful artift,* Saw makers 

 allured me fome time ago that the faw-makers firft harden their fteel . th( T n r 

 plates in the ufual manner, in which ftate they are more or lefsfoften it by 

 contorted or warped, and are brittle; — that they then blaze J j" g ?*J i i. 

 them; which procefs deprives them of ail fpringinefs, fo by blueing. 

 that they may be bended and hammered quite flat, which is a 

 delicate part of the art of faw making; — and that they blue them 

 on an hot iron which renders them ftiff and fpringy without 

 altering the flatnefs of their furface. Mr. H. finds that foft Soft fteel Mu«d. 

 unhardened fteel may be rendered moreelaftic by blueing, and Har , d fteeI e *~ 



J J t>' pands more by 



that hard fteel is more expanfible by heat than foft. heau 



It is very difficult to reafon or even to conjecture upon thefe 



fa&s. They certainly deferve to be verified by a direct procefs 



of examination, which I intend to make, and (hali ftate the 



refults in our next number. N. 



* See his banking far time p : eces in our XI. Vol* page 114. 



Cor- 



