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ON THE HARDNESS OF METALS AND ALLOYS. 115 
bears on the piece of metal Z to be experimented on, and 
this is supported on a solid piece of iron G. The support 
or point of resistance W is lowered or raised by the screw 
M, and when, therefore, this screw is turned the whole of 
the weight on the lever is borne by the support I and the 
screw M. When it is necessary, by turning the screw M, 
the weight on the lever is re-established on the bar, and 
experimented upon. 
When we wished to determine the degree of hardness of 
a substance we placed it on the plate G, and rested the 
point F upon it, noticing the exact mark on a on the bar 
A, and then gradually added weights on the end of the 
lever C until the steel point F entered 3-5mm. or 0°128 of 
an inch during half an hour, and then read off the weight. 
A result was never accepted without at least two experi- 
ments were made, which corresponded so far as to present 
a difference of only a few pounds. The following table 
gives the relative degree of hardness of some of the more 
common metals. We specially confined our researches to 
this class, wishing the results to be practically useful to 
engineers and others who have to employ metals, and 
often require to know the comparative hardness of metals 
and alloys. 
Weight Calculated Cast 
Names of Metals. employed. Tron = 1000 
Staffordshire Cold Blast Cast 
Tron — Grey, No. 3 
Steel 
Wrought Iron* 
Platinum 
Copper — pure 
Aluminium 
Silver — pure 
Zine GOs weaves teetett capes. 
Gold GOs ichecapaasovcestes 
Cadmium do 
Bismuth do. ...ccccccceccecsveeee 
Tin Or % i Ser deiieteduars's 
Lead OG. vx4 cas aathe cosaeaene 
* This wrought iron was made from the above-mentioned cast iron. 
