ON THE HARDNESS OF METALS AND ALLOYS. Its 
quantity of so malleable a metal as copper should so 
suddenly render the alloy brittle, for the 
Alloy Cu Sn2 
or 
Copper ee 21 hes is not SHEER, 
Tae eaens Yaro 
whilst the alloy Cu Sn 
or 
Copper wean 34°98 in brite, 
fT ae ae 65:02 
Therefore the addition of 14 per cent of copper renders a 
bronze alloy brittle. This curious fact is observed in all 
the alloys with excess of copper, Sn Cuz, Sn Cuz, Sn 
Cus, Sn Cu;, until we arrive at one containing a great 
excess of copper, viz., the alloy Sn Cujo, consisting of 
copper 84°68 and tin 15°32, when the brittleness ceases ; 
but strange to say this alloy, which contains four-fifths of 
its weight of copper, is notwithstanding nearly as hard 
asiron. This remarkable influence of copper in the bronze 
alloys is also visible in those composed of 
Sn Cu,;, containing 88°97 of copper. 
Sn Cugo, - 91°49 a 
Sn Cuz;, P| 93°17 3 
Copper acquires such an increased degree of hardness by 
being alloyed with tin or zinc that we thought it inter- 
esting to‘ascertain if alloys composed of these two metals 
would also have a greater degree of hardness than that 
indicated by theory; we accordingly had a series of alloys 
prepared in equivalent quantities, and these are the results 
arrived at: 
