262 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Heat Treatment of Copper-zinc Alloys.* — G. 1). Bengough and 

 0. F. Hudson have investigated the effect upon niicrostructure and 

 mechanical properties of Muntz metal of annealing at different tem- 

 peratures. The brass contained 60'43 p.c. copper, 39*21 p.c zinc, 

 0*33 p.c. lead, and was rolled hot to round bars, which were finally 

 reduced slightly by cold rolling. In this state the metal had a 

 considerably higher tensile strength and elongation than in the cast 

 condition. Brass of this composition is normally constituted of a and 

 /3 solid solutions. On heating, a dissolves progressively in (3 with rise 

 of temperature ; at 720° C. /? is the sole constituent. By quenching at 

 different temperatures, alloys containing the two phases in different 

 proportions may be obtained. Test bars quenched after heating to a 

 temperature high enough to produce a notable increase in the proportion 

 of /3 give a slightly increased maximum tensile stress and a greatly 

 diminished elongation. /3 appears to be brittle. Dilute ammonia 

 solution was used for etching ; a etched light, ft dark. By varying the 

 strength of the solution a completely reversed effect may be produced. 



Piping and Segregation.! — H. M. Howe and B. Stoughton have 

 studied these phenomena in ingots cast from wax containing green 

 copper oleate (1'5 p.c). The wax was coloured by the addition of a 

 little red cerasine, which does not segregate. The predictions made by 

 Howe concerning the influence of casting conditions upon piping and 

 segregation were verified. £ 



Measurement of Extension of Tensile Test-pieces. § — W. J. Lambert 

 claims great accuracy, combined with simplicity, for a method of measuring 

 small extensions, which consists in projecting a magnified image of the 

 gap between knife edges attached to the ends of the test-piece, on the 

 focusing screen of a photomicrographic apparatus. The extension is 

 readily calculated from the increase in width of the image of the gap, 

 given the magnification. 



Recovery of Steel from Overstrain. || — E. C. Hancock has show n 

 that a carbon steel and a steel containing 3 " 5 p.c. nickel, when over- 

 strained in either tension or compression, lose their elasticity for stresses, 

 both of the same and of the opposite kind. Recovery takes place 

 through rest and more rapidly on warming. 



Influence of Stress on the Electrical Conductivity of Metals.1T 

 W. E. Williams has determined the effect of hydrostatic pressure upon 

 the resistance of wires of lead, aluminium, bismuth, and manganin. 

 The resistance of lead and aluminium is diminished by pressure, that of 

 bismuth and manganese increased, the change in each case being 

 proportional to the pressure. 



* Journ. Soc. Chem. Ind., xxvii. (1908) pp. 43-52 (30 figs.). 



t Bull. Amer Inst. Mining Engineers, xvi. (1907) pp. 561-73 (17 figs.). 



X See this Journal, 1907, p. 382. 



§ Proc. Inst. Civil Eng., clxix. (1907) pp. 349-51 (2 figs.). 



|| Phil. Mag., xiii. (1907) pp. 688-93 (8 figs.). 



1 Tom. cit., pp. 635-43 (3 figs.). 



