118 



Messrs. F. C. Calvert and R. Johnson on the 



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 colour than the ordinary alloys of com- 

 merce. The only reason that we can give why it has not been 

 introduced into the market is, that when the amount of zinc em- 

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

 that the manufacturers have deemed it advisible not to exceed 

 that proportion. If, however, they had increased the quantity 

 to exactly o0'68 per cent, and mixed the metals well, they would 

 have obtained an alloy as rich in colour as if it had contained 

 90 per cent, of copper, and of a hardness three times as great as 

 that given by calcvdation. 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 facihty 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 mix- 

 ture of metals, as alloys are generally considered to be. Our re- 

 searches on the conductibility of heat by alloys, which we have 

 recently presented to the Royal Society, leave no doubt that 

 many alloys are definite chemical compounds. 



* These alloys all contain tin. 



J 



