CHEMICAL SCIENCE. 



213 



These results show that all the alloys containing an excess of copper are 

 much harder than the metals composing them, and, what is not less interest- 

 ing, that the increased degree of hardness is cine to the zinc, the softer metal 

 of the two which compose these alloys. The quantity of this metal must, 

 however, not exceed 50 per cent, of the alloy, or the alloy becomes so brittle 

 that it breaks as the steel point penetrates. We believe that some of these 

 alloys, with an excess of zinc, and which are not found in commerce, owing 

 to their white appearance, deserve the attention of engineers. There is in 

 this series an alloy to which we wish to draw special attention, viz., the alloy 

 Cu Zn composed in 100 parts of 



Copper, 49-32 



Ziuc, 50-68 



100-00 



Although this alloy contains about 20 per cent, more zinc than any of the 

 brasses of commerce, still it is, when carefully prepared, far richer in color 

 than the ordinary alloys of commerce. The only reason that we can give 

 why it has not been introduced into the market is, that when the amount of 

 zinc employed exceeds 33 per cent., the brass produced becomes so white 

 that the manufacturers have deemed it advisable not to exceed that propor- 

 tion. If, however, they had increased the quantity to exactly 50'08 per cent, 

 and mixed the metals well, they would have obtained an alloy as rich in 

 color as if it had contained 90 per cent, of copper, and of a hardness three 

 times as great as that given by calculation. In order to enable engineers to 

 form an opinion as to the value of this cheap alloy, we give them the degrees 

 of hardness of several commercial brasses : 



The alloy Cu Zn possesses another remarkable property, viz., the facility 

 with which it is capable of crystallizing in prisms half an inch in length, of 

 extreme flexibility. There is no doubt that this alloy is a definite chemical 

 compound, and not a mixtui'e of metals, as alloys are generally considered 

 to be. Our researches on the conductibllity of heat by alloys, recently pre- 

 sented to the Royal Society, leave no doubt that many alloys are definite 

 chemical compounds. 



* These alloys all contain tin. 



