636 SUMMARY OF CURRENT RESEARCHES. 



of organic nitro compounds, were found to act slowly and to give fine 

 preparations. A relationship was observed between the speed of etching 

 and the degree of molecular dissociation of the liquid. P. Lejeune, 

 following up this point, indicates the effect of viscosity and dielectric 

 constant. By etching exactly similar pieces of steel under identical 

 conditions, using different reagents, the etching velocity of the solutions 

 may be compared ; 4 p.c. solutions of picric acid in acetonitrile, pro- 

 pionitrile, methyl-alcohol, and ethyl-alcohol were compared ; the order 

 given is that of their activity, the last being the slowest in etching. 

 This is the order given for the electric conductivity of solutions of 

 sodium chloride in these liquids. It is necessary when comparing the 

 etching velocity of such solutions that the solvents should be anhydrous, 

 traces of moisture increasing the ionisation. A method of photo- 

 graphically recording the progress of etching is suggested. 



Iron-Nickel-Manganese-Carbon Alloys.* — H. C. H. Carpenter, 

 K. A. Hadfield, and P. Longmuir give as the seventh report to the 

 Alloys Research Committee, the results of an exhaustive investigation of 

 the properties of ten alloys containing 0'79 to 1*03 p.c. manganese, 

 0'4 to - 52 p.c. carbon, nickel varying from to 19 '9 p.c. The 

 results of numerous mechanical tests and physical measurements are 

 fully set out in tables and as curves. The range of solidification and the 

 critical ranges on heating and cooling were determined. The lowering 

 of the critical range on cooling is fairly uniform up to 4 p.c. nickel. 

 Further increase of nickel causes a change of character in the cooling 

 curves, the critical ranges being spread over a wide interval of tempera- 

 ture. The authors' metallographic results agree on the whole with 

 Guillet's.f A 5 p.c. solution of picric acid in alcohol, used at the outset 

 as an etching reagent, was replaced by 1 p.c. nitric acid in alcohol, giving 

 the same results more quickly. The alloys were examined as forged, and 

 after being thermally and mechanically treated in various ways ; they are 

 classified as follows : — 



Cast alloys . . to 5 or 6 p.c. nickel . . Pearlitic 



5 or 6 to about 16 p.c. nickel . . Martensitic 

 Over 16 p.c. nickel .. .. Polyhedral 



Forged alloys . . to 4 p.c. nickel . . . . Pearlitic 



5 to 20 p.c. nickel . . . . Martensitic 



No evidence for the existence of a carbide of nickel was found. The 

 effect of mechanical work on the alloy with 19*9 p.c. nickel was to 

 change its microstructure and cause it to become magnetic. A dark 

 etching constituent was produced. The alloy previous to deformation 

 gave a white polyhedral structure on etching. The polyhedral structure 

 is restored wholly or in part by heating at 900° C. J. 0. Arnold 

 criticised the authors' method of taking critical range curves. 



Peiece, B. O. — On the Permeability and the Retentiveness of a Mass of Fine 

 Iron Particles. Proc. Am. Acad. Arts and Sci., xlii. (1906) 



pp. 87-91 (2 figs.). 

 Osmond, P.— French Contributions to the Progress of Scientific Metallurgy. 



[Recent metallographical research in France is briefly reviewed in this 

 paper.] Rev. Metallurgie, iii. (1906) pp. 365-81. 



* Proc. Inst. Mech. Eng., 1905, pp. 857-959 (87 figs.) ; discussion, pp. 959-1041. 

 f Bull. Soc. de l'Enc, 1903. 



