M \ . 



iii|Miuiul of iron, carbon, and 



redness and cooled suddenly, as by immersion in water 



tmeil. Tin- degree of hardness produced varies with the 

 ; L<, ,,i poosfag . th.- MM! . ipid | .'. baiisd itsej I ml 

 the hanier does it become. M nl steel U softened by the 

 proiiMi of annmKnff, which consists in heating th hardened 

 steel to redness, and then allowing it to ox- Kurd 



ened steel w tomptrwi, or baa its degree of hardness lowered 

 :> heated to a temperature considerably below that of a red 



The higher the temper* 

 the hardened steel is raised to, the lower does its temper ' 



Cotf-AordttK is in the name given to the process 



:> the surfaces of articles made of wrought iron are 



t-t-l into steel, and consists in heating the articles in 



!i substances i .u bone-dust, 



horn shavings, or yellow prnssiate of potash. This process 



is gener >.*! to the articles after they are completely 



finished by the machine took ..uul. The coating of 



steel produced on the article l.y this process U hardened by 



< the article suddenly in * 



Copper. This iuUl has a reddish brown colour, and when 



pun- IN ' <-t Y malleable and ductile, either when cold or hot, so 



my be rolled or hammered into thin pistes, or drawn 



if ^ 'races of impurities cause britUeness, 



although from 2 to 4 pt-i f phosphorus increases its 



tenacity and ilu i pper is a good coni heat and 



of elect r -pper ia largely used for making alloys. 



' contains two parts by weight of copper to 

 one of sine. Munis mttal consists of three parts of copper to 

 two of . Mloys consisting of copper and tin are call.. I 



bronze or yun-matal. Bronze is harder the greater the pro- 

 port i A ; five parts of copper to one 



of tin I'pNluce a very hard bronse, and ten of copper to one 

 of tin is the composition of a soft bronse. /'AoqpAor 6rons0 

 l*r and tin uh a little phosphorus; it has thi 



