392 SUMMARY OF CURRENT RESEARCHES RELATING TO 



strained specimens is hastened by raising the temperature, and retarded 

 or arrested by lowering the temperature. The formation of slip-hands 

 on a polished surface, subjected to tensile stress, is described. 



Metallography of Quenched Steels.*— M. Kourbatoff has experi- 

 mented with a large number of etching reagents, to determine which are 

 the most useful for the differentiation of the constituents of quenched 

 steels. Three samples of steel, selected to give a great variety of con- 

 stituents, were etched with the different solutions ; they were (1) steel 

 containing 1 ■ 8 p.c. carbon, quenched during the recalescence ; (2) the 

 same, quenched when one end of the specimen was at its melting point, 

 the other end being cold; (3) steel containing 15 p.c. nickel, 0*8 p.c. 

 carbon. The possible causes of the varying colorations of different 

 constituents upon etching are discussed, the author concluding that the 

 colorations are probably due to the formation of complex organic com- 

 pounds, in which the nitro groups present in many reagents are con- 

 cerned. The rapidity of action of solutions of nitric or picric acids 

 appears to depend on the electric conductivity of the liquid. The most 

 suitably reagents for distinguishing the constituents are : (a) solution of 

 4 p.c. nitric acid in iso-amyl alcohol ; (J) solution of 20 p.c. hydrochloric 

 acid in iso-amyl alcohol, to which is added I of its volume of a satu- 

 rated solution of nitraniline or nitro-phenol in ethyl alcohol. The best 

 reagents for colouring sorbite and troostite without acting upon other 

 constituents are : (c) equal parts of a solution of 4 p.c. nitric acid in acetic 

 anhydride, methyl alcohol, ethyl alcohol, and iso-amyl alcohol ; (d) 3 parts 

 of a saturated solution of nitro-phenol, 1 part of a 4 p.c. solution of 

 nitric acid in ordinary alcohol. 



From experiments on re-heating quenched samples, the author con- 

 cludes that : (1) during re-heating austenite changes to sorbite ; (2) 

 martensite decomposes into layers of cementite and crystals of sorbite ; 

 (3) at 800° the whole of the martensite and austenite are changed 

 to sorbite and cementite ; (4) troostite remains unchanged up to 400°. 

 The hardness of austenite appears to be variable in different samples 

 and in different parts of the same sample. 



The Cooling of Steel in Quenching.!— P. Lejeune gives a number 

 -of cooling curves, obtained by the Saladin photographic method— in 

 which two galvanometers are employed— of samples of steel quenched in 

 different liquids. The author concludes that quenching in small volumes 

 of mercury is less rapid than quenching in water. The influence of the 

 viscosity, boiling-point, and specific heat of the quenching liquid were 

 also investigated. 



Aluminium Steels. J — L. Guillet has continued his researches on 

 alloy steels. Two series were employed, one containing 0*15 p.c, the 

 other 0*75 p.c. carbon, the aluminium varying in each series from 

 to 15 p.c. Physical properties and microstructure were studied in the 

 steel (1) as forged, (2) quenched, (3) annealed. Up to 2 p.c. the 

 influence of aluminium is slight. The pearlite appears to be more 



* Rev. Metallurgie, ii. (1905) pp. 169-86 (23 figs.). 



t Tom. cit., pp. 299-311 (10 figs.). 



J Tom. cit., pp. 312-27 (24 photomicrographs). 



