678 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



solutions, the curve is U-shaped ; (3) solid solutions of limited con- 

 centration are formed, the curve is modified accordingly, showing an 

 inflection at the limit of saturation of the mixed crystals ; (4) a com- 

 pound is formed, the curve having a maximum at the concentration 

 corresponding to the compound. These rules are compared with those 

 expressing the relation of hardness and electrical conductivity to con- 

 centration. 



Nitrogen and Metals at High Temperatures.* — I. Shukow has 

 made determinations of the dissociation pressures of metal-nitrogen 

 alloys. The continuous increase of the dissociation pressure with 

 nitrogen content in the case of chromium and manganese proves the 

 alloys to be solid solutions, not compounds. With aluminium the 

 dissociation pressure is constant for a given temperature, and inde- 

 pendent of nitrogen content, indicating the presence of an aluminium- 

 nitrogen compound. From these results, and from those obtained in 

 determinations of electrical resistance of metal-nitrogen alloys, the 

 author concludes that nitrogen forms solid solutions but no compounds 

 with manganese, chromium, and titanium. 



Effect of Silicon and Sulphur on Cast-iron.f — It is well known 

 that sulphur tends to make cast-iron white by retaining the carbon in 

 the combined state, and that silicon tends in the opposite direction. 

 J. E. Stead reviews the work of previous investigators, and gives the 

 results of a micro-chemical study of the causes of these phenomena. 

 The three pig-irons examined, which illustrate well the effects con- 

 sidered, contained : — 



The white iron contained no iron-iron-carbide eutectic, its place being 

 taken by the ternary eutectic of the iron-phosphorus-carbon system. 

 These and other alloys were submitted to various chemical treatments, 

 to separate the carbides, and metallurgical treatments, such as re- 

 melting with additions of sulphur or of manganese, and were micro- 

 scopically examined in their different states. The author concludes 

 that carbide of iron in presence of iron-sulphide crystallizes with an 

 amount of sulphur not exceeding about ■ 1 p.c. of the weight of the 



* Journ. Russ. Phys. Chem. Ges., xlii. (1910) pp. 40-55, through Journ. Soc. 

 Chem. Ind., xxix. (1910) p. 572. 



t British Assoc, 80tn Rep., Sheffield, 1910. Chemical Section, President's 

 Address, 13 pp. (9 figs.). 



