ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 635 



as a statement of the general principles which govern the relationship of 

 constitution to physical properties of alloys. 



The Iron and Steel Magazine.* — This Journal (formerly the 

 " Metallographist ") has ceased to be issued as a separate publication, 

 having been taken over by " Electrochemical and Metallurgical In- 

 dustry," with which it is now incorporated. It is a matter for regret 

 that a journal which has rendered such excellent service in the advance- 

 ment of metallography should no longer be published separately. The 

 back volumes, all of which we believe may still be obtained, contain 

 much of the valuable literature dealing with the application of micro- 

 scopy to metals. 



Measurement of the Elastic Limit of Metals.j — Guillery describes 

 a method by which the variations in electric resistance of a test-piece 

 are recorded during a tensile test. A current of 25-30 amperes per 

 square centimetre of section is passed through the test-piece and a 

 compensating resistance. A galvanometer is so connected with the test- 

 piece and resistance that its deflections indicate variations of resistance 

 in the test-piece. The galvanometer deflections are plotted against the 

 loads, the elastic limit being indicated by a break in the curve. Consider- 

 able differences were found to exist between the results obtained in this 

 manner and the figures given by the direct measurement of strain in the 

 usual way. H. le Chatelier comments on the results. 



Nickel-Chromium Steels.f — The twenty-nine alloys examined by 

 L. Guillet had the following analyses (approximately). 



First series (9 steels) : 

 Carbon ■ 2 p.c. 



Nickel 5 p.c, chromium 3, 10, 20 p.c. 

 „ 12 „ „ 3,10,20 „ 



„ 30 „ „ 3, 10, 20 ,, 



Second series (9 steels) : carbon 0*8 p.c, nickel and chromium as in 

 first series. 



Third series (5 steels) : carbon " 3 p.c, nickel 2 ■ 5 p.c, chromium 

 * 5-5 p.c. 



Fourth series (6 steels) : carbon ■ 2 p.c, nickel 5-6 p.c, chromium 

 • 5-6 p.c. 



The microstructure and mechanical properties of these steels are 

 generally such as might be inferred from the properties of nickel steels 

 and chromium steels, both of which have been investigated by the 

 author. The effect of the chromium is added to that of the nickel. 

 The following percentages are equivalent: 1*65 carbon, 29 nickel, 

 1 8 chromium. Fearlitic nickel chromium steels are harder when quenched 

 than pearlitic nickel steels in the same state, y-iron nickel chromium 

 steels have a higher elastic limit than y-iron nickel steels. 



Etching Velocity of Metallographic Reagents.§ — A number of 

 etching reagents investigated by Kourbatoff,|| chiefly alcoholic solutions 



* Electrochem. and Met. Ind., iv. (1906) p. 253. 



t Rev. Metallurgie, iii. (1906) pp. 331-42. 



X Tom. cit., pp. 462-84 (17 photomicrographs). § Tom. cit., pp. 426-7. 



)| See this Journal, 1905, p. 392. 



