212 



ANNUAL OF SCIENTIFIC DISCOVERY. 



When we wished to determine the decree of hardness of a substance, we 

 placed it on the plate, and rested the point upon it, noticing the exact mark 

 on the bar, and then gradually added weights on the end of the lever until 

 the steel point entered 3'5 mm. or OT.J8 of an inch during half an hour, and 

 then read off the weight. A result was never accepted without at least two 

 experiments being made, which corresponded so far as to present a difference 

 of only a few pounds. The following table gives the relative degree of hard- 

 ness of some of the more common metals. "We specially confine 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. 



This table exhibits a curious fact, viz., the high degree of hardness of cast 

 iron as compared with that of all other metals ; and although we found alloys 

 which possessed an extraordinary degree of hardness, still none were equal 

 to cast iron. 



The first series of alloys we shall give, is that of copper and zinc. 



* This wrought iron was m.-ide from the above mentioned ca*t iron. 



t To calculate the hardness of an alloy, we multiplied the per centape quantity of 

 each metal by the respective hardness of that metal, added the two results together, 

 and divided by 100. The quotient is the theoretical hardness. 



