186 SCIENCE PROGRESS. 



structure of plates of pure iron alternating with thinner 

 plates of a carbide of iron. Osmond 1 considers, however, 

 that as many as five crystalline ingredients can be detected 

 in steel, and that iron itself can, by processes of hardening 

 and tempering, be brought into at least three allotropic 

 states. Let us hope that increasing knowledge will simplify 

 and not further complicate the views held on this subject. 



It is certain that although the scientific explanation of 

 all the phenomena revealed by the microscopic examina- 

 tion of alloys may not come to us for some time, yet 

 technical workers who use the microscope will find, 

 and are finding, a correlation between microscopic structure 

 and mechanical properties that cannot fail to be of enor- 

 mous value to the engineer. 2 For example, the microscope 

 throws light on that important section of metallurgy, the 

 use of small admixtures of reducing agents, such as zinc or 

 sodium with copper. It also promises to explain the curious 

 change by which some bronzes are hardened by reheat- 

 ing. 



Behrens, in common with many other students of the 

 subject, is disposed to attribute definite chemical formulae 

 to some of the constituents found in an alloy, especially to 

 those alloys which solidify homogeneously ; but the writer 

 inclines to the view that these eutectic alloys, such as Levol's 

 Cu 2 Ag 3 , and others of the same kind, may be solid solutions 

 and may have no claim to be regarded as chemical com- 

 pounds. Whether this be so or not, it is certain that the 

 arguments as to definite chemical composition brought for- 

 ward bv each worker from the use of his own methods, must 

 be tested and supported by other methods before they can 

 be generally accepted. 



Dr. Foerster, in a valuable series of articles on the 

 " Chemical Nature of Alloys," * to which the present writer 

 is indebted for several references, suggests that alloys of 



1 M^thode G£n£rale pour l'Analyse Micrographique des Aciers au 

 Carbone. Bull, de la Societe d' Encouragement, x., p. 480, 1895. 

 2 Roberts Austen, Nature, Aug. 15, 1895. 

 8 Naturwissenschaji 'lithe Rundschau, 1894. 



