788 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Binary Systems. — J. J. van Laar* develops mathematically the 

 theory of the form of the melting-point or solidification-point curves of 

 binary systems when the solid phase is an amorphous solid solution, or 

 mixed crystals, of the two components. In a later paperf the author 

 deals with the cases in which a compound occurs. 



Hardness of Metallic Solid Solutions and Chemical Compounds. 

 N. S. Kurnakow and S. F. Zemczuzny| collate the results obtained by 

 themselves and others relating to the hardness of binary alloys. When 

 the metals form a continuous series of solid solutions, "the curve 

 showing relation of hardness to composition is continuous and passes 

 through a maximum, this maximum corresponding to the minimum of 

 electrical conductivity. The occurrence of a chemical compound, which 

 may be harder or softer than the two metals, causes a break in the 

 curve. If the alloys are mechanical mixtures of the two metals, the 

 curve is a straight line. The hardness curve of more complex binary 

 systems is a combination of the above types. 



C. Benedicks§ discusses the above paper, and points out that the 

 character of the curves connecting electrical properties with composition 

 indicates that, while in the case of metallic aggregates conductivity is a 

 suitable criterion of composition, resistance is more suitable for solid 

 solutions. 



Formation of Alloys by Pressure. ||—G. Masing has submitted 

 mixtures of finely divided metals to pressures of 1000-5000 atmospheres, 

 to ascertain if alloys similar to those obtained by melting could thus be 

 produced. The numerous binary mixtures pressed are classified accord- 

 ing to their behaviour upon solidification from the corresponding binary 

 melts : — (1) the two metals solidify as pure components ; (2) com- 

 pounds are formed, but no solid solutions ; (3) a continuous series of 

 solid solutions is formed ; (4) interrupted series of solid solutions are 

 formed. The block obtained by pressing was examined microscopically, 

 and heating curves were taken. The author concludes that the mass 

 obtained by compressing file-dust of two metals together consists 

 exclusively of grains of the two metals ; in no case could the presence 

 of solid solutions or compounds be established. Thus pressure does not 

 induce the formation of compounds or solid solutions. The only 

 possible influence of pressure is to bring about more intimate contact 

 between the metals. Pressed mixtures differ essentially in structure 

 and properties from alloys obtained by melting whenever those alloys 

 contain solid solutions or compounds. If, however, two metals can 

 form a compound, noticeable amounts of the compound may be formed 

 in the solid state. If solid solutions occur in the system, diffusion may 

 take place in the solid state at ordinary temperatures, and more rapidly 

 at higher temperatures. The heating curve of a pressed block differs 

 from that of the alloy obtained by melting, and accordingly cannot be 

 reproduced by a second heating of the same mass. 



* Zeitschr. Phys. Chem., lxiii. (1908) pp. 216-53 ; lxiv. (1908) pp. 257-97 (53 figs.), 

 t Op. cit., lxvi. (1909) pp. 197-237 (14 figs.). 

 % Zeitschr. Anorg. Chem., lx. (1908) pp. 1-37 (12 figs.). 

 § Op. cit., lxi. (1909) pp. 181-6 (1 fig.). 

 || Zeitschr. Anorg. Chem., lxii. (1909) pp. 265-309 (43 figs.). 



