ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 661 



powdered copper-tin alloys, with the object of measuring the chemical 



affinities; existing between the two metals. The alloys containing 

 0-56 p.c. copper precipitate lead from lead chloride solution in the same 

 way as pure tin does : they therefore contain free tin. By similar 

 reasoning from their other experimental results, the authors deduce the 

 existence of two compounds, Cu 3 ftn and Cu 5 Sn 2 , or Cu 2 Sn. 



Tellurides of Arsenic and Bismuth.* — In the tellurium-arsenic 

 system H. Pelabon finds minima at 329° C. and 355° C, maxima at 

 362° C. (As 2 Te 3 ) and 358° C. In the tellurium-bismuth system there 

 are two eutectic points, 410° C. (15 p.c. bismuth) and 263° C. (1 p.c. 

 tellurium). A maximum at 583° C. indicates the compound Bi 2 Te 3 . The 

 author calculates the cryoscopic constant of tellurium from the lower- 

 ing of its melting point by solution in it of As 2 Te 3 , Bi 2 Te 3 , and other 

 tellurides, arriving at the mean value 520. 



Occluded Gases in Special Nickel Steel. f — Gr. Belloc has de- 

 termined the composition of the gases evolved from a steel containing 

 45 p.c. nickel, ■ 15 p.c. carbon, at different temperatures 4 The occluded 

 gases were C0 2 (all given off below 520° C), CO (increasing to 75 p.c), 

 N (all evolved above 520° C, and only found in small amount), and H. 

 When the steel was in the form of wire, the total volume of gases was 

 10 times that of the steel, while with drillings from the ingot the 

 volume was 3| times the volume of the steel. The greater part of the 

 gas was evolved while the iron was in the y state and the nickel in 

 the ft state. 



Factors of Safety in Marine Engineering^ — J. O. Arnold points 

 out that, although in structural steel the ratio of maximum stress to elastic 

 limit is approximately 2 to 1 in the majority of cases, yet in an im- 

 portant number of instances the ratio differs very widely from this. 

 Over-annealed steel has a very low elastic limit, and the factor of 

 safety calculated from the maximum stress of such steel would 1 >e 

 dangerously low. Over-annealing (excessively slow cooling from a high 

 temperature) causes the formation of pearlite in which the lamellar 

 structure is highly developed, and the partial separation of pearlite into 

 massive cementite and ferrite. The author explains the formation of 

 decarbonised " ghosts," on the theory that dissolved phosphide of iron 

 expels carbon from a segregated spot. The author's alternating stress 

 test is described, and though its theoretical defects are admitted, it is 

 recommended in preference to Wohler or similar tests in which the 

 elastic limit is not exceeded, for the detection of brittle material. The 

 possible danger in using steels of high elastic limit is indicated. 



Planimetric Analysis of Alloys. || — A. K. Huntington and C. H. 

 Desch describe the method of determining the proportions of the 

 component metals by microscopic examination of alloys. A constituent 



* Comptes Rendus, cxlvi. (1908) pp. 1397-1400. 



t Op. cit., cxlvii. (1908) pp. 244-5. 



{ See this Journal, 1908, p. 124 



§ Engineering, lxxxv. (1908) pp. 565-6, 59S-601 (16 figs.). 



|| Tom. cit., p. 589. 



