ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 391 



however, do not give good results : 2 p.c. ammonium nitrate has been 

 found most satisfactory, especially at 40° C. Persulphates have also 

 been employed. Reaction velocity is of importance, and is in most 

 cases increased by rise of temperature. 



The Effects of Momentary Stresses in Metals.* — B. Hopkinson gives 

 the results of his experiments in which the extension of copper and iron 

 wires, subjected to momentary stresses, was measured. A piece of wire, 

 of No. 10 gauge, and about 30 ft. long, was hung vertically, being 

 fixed at its upper end. It was kept taut by a tension (20 to 200 lbs.) 

 applied at the lower end, and a cylindrical 1 lb. weight allowed to fall 

 down the wire, being arrested by a stop fixed to the end of the wire. 

 The extension on 20 in. was determined by an arrangement devised for 

 the purpose, and was found to be in close agreement with the extension 

 calculated from J. Hopkinson's formula. The author concludes that 

 iron and copper wires may be stressed much beyond the static elastic 

 limit, and even beyond their static breaking loads without the pro- 

 portionality of stresses and strains being substantially departed from, 

 provided that the time during which the stress exceeds the elastic limit 

 is of the order of T ^g-o second or less. 



Further Observations on Slip-Bands in Metallic Fractures. Pre- 

 liminary Note.t — W. Rosenhain has employed a new method of investi- 

 gating the micro-structure of metals, to meet the criticisms of F. Osmond 

 and others on the conclusions reached by J. A. Ewing and the author, 

 as to the nature of slip-bands. The difficulties met with in the exarni- 

 ation of a transverse section of a metallic surface, upon which slip- 

 bands had been produced, were overcome by electro-deposition of another 

 metal on the surface. The piece of metal was then cut through and 

 polished, a sectional elevation of the surface being thus obtained. 

 Strips of the mildest steel were polished along a short portion of their 

 length, and were then strained in tension to produce slip-bands on the 

 polished surface. A thin film of copper was deposited from a bath of 

 copper cyanide. The pieces were then removed to the usual copper 

 sulphate bath, and a thicker layer (4-5 mm.) deposited. Sections were 

 made, roughly parallel to the direction of the original tensile strain, 

 at right angles to the surface showing slip-bands. Calcined magnesia 

 was used as the final polishing medium, as rouge eroded the surface. 

 The film of metal smeared over the boundary was removed by slight 

 etching with picric acid. A clearly defined boundary line between iron 

 and copper was then visible, showing well marked steps or serrations. 

 The author concludes that the sectional views of slip-bands thus obtained, 

 strongly confirm the theory of deformation by slip. He suggests that 

 the method of investigation described might be applied to the study of 

 a number of questions, and has employed it in obtaining sections of 

 fractures, with satisfactory results. 



Effects of Stress upon Metals. % — E. G. Crocker describes the 

 behaviour of metals when subjected to stress. The recovery of over- 



• Proc. Roy. Soc, lxxiv. (1905) pp. 49S-50G (2 figs.). 



t Tom. cit.. pp. 557-62 (4 tigs.). 



I English Mechanic, lxxxi. (1905) pp. 146-7. 



