30 Laboratory Arts 



and the resistance to wear offered by the other material. It 

 is used in constructional work, e.g. rods supporting weights, tie 

 rods on apparatus, screw shafts. Callipers l and similar tools 

 and appliances are often made of this material. 



Both cast and mild steel may be obtained in almost any 

 desired size, sheets ^" thick, of any area, or rods of any shape 

 or size in section being listed by tool makers. An old saw 

 blade answers many purposes admirably, and will serve as 

 a stock from which this material may be drawn as occasion 

 demands. Steel is cut with a hack saw, or a "cold steel 

 chisel." 



Many steels containing small quantities of nickel, tungsten, 

 vanadium, chromium, etc., are now available for special pur- 

 poses. These, however, are not of great service to the makers 

 of laboratory apparatus of the type contemplated in this 

 volume, though unquestionably of immense value in the 

 manufacture of tools, of parts of machinery subject to excessive 

 vibration and in similar special cases. 



Brass, Gunmetal, Bronze, Phosphor Bronze. 

 These alloys all contain copper as the principal constituent, 

 the secondary constituents endowing the alloy with various 

 valuable properties. 



Brass is a very variable material ; it differs in composition, 

 density, and colour, the quality being difficult to judge until 

 working commences. As a rule it may be taken that " white " 

 (light-coloured) brass is of inferior quality, though some grades 

 of bright yellow metal, such as that of which paper fasteners 

 are made, are extremely valuable because of their pliability. 

 These, however, are special preparations. " White " brass is 

 usually cast ; it contains much zinc, and is more brittle, and 

 more liable to contain " blow-holes " than the darker grades, 

 which, containing more copper, are more expensive. 



The price of brass is not altogether dependent upon the 

 amount of copper present, though this is an important factor ; 

 but also upon the fact that extra copper means a higher melting 

 point, and consequently more coal for the preparation of the alloy. 



1 Callipers should be made of " shear " steel, which is much harder than 

 mild steel, though bought tools are frequently made as described. 



