70 MODERN SCIENCE OF METALS 



Metallurgy has set itself ; since alloys may be made 

 of the majority of metals taken two, three, four 

 or more at a time, and since the presence of even 

 small proportions of another metal often serves 

 to modify these phenomena to a profound degree, 

 this task is a truly colossal one and is only being 

 slowly accomplished. At the present time some 

 five or six systems of alloys of two metals have 

 been really thoroughly studied ; for the remainder 

 of these relatively simple "binary" alloys we still 

 have to rely upon data which are only rough 

 approximations. Of systems of alloys of three 

 metals, only two or three have been closely studied, 

 while systems of four metals are only approached 

 with much difficulty. As it happens, however, the 

 study of the alloys of two metals only has already 

 served to outline most of the fundamental principles 

 which underlie the constitution and structure of 

 all alloys and the changes which they undergo, 

 and these results have proved unexpectedly fruitful 

 in technical practice. 



To one class of practical results we have already 

 referred, viz. the power over the properties of the 

 alloys of iron with carbon and with nickel and 

 chromium, which flows from our knowledge of the 

 changes which they undergo when heated to various 

 temperatures and cooled at various rates. Indeed, 

 it is not too much to say that the entire develop- 

 ment of modern special "alloy" steels could not 

 have taken place had not the New Metallurgy 



