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XCV. Regular Surface Markings in Stretched Wires of Soft 

 Metals. By E. N. da 0. Andrade, B.Sc, Ph.D., late 

 1851 Exhibition Scholar of University College, London *• 



[Plate XIII.] 



IN a study of the flow in metals, an account of which is 

 now in course of publication, experiments were made 

 with wires of solid mercury. These were prepared by 

 rilling with mercury a mould composed of two hollow glass 

 hooks connected to each end of a thin glass tube by rubber 

 junctions, and then immersing the whole in a bath of solid 

 carbon dioxide and alcohol ; when the mercury was frozen 

 solid the glass tube, previously scored with a diamond, was 

 quickly broken off, leaving a wire of solid mercury fastened 

 into a glass hook at each end. For the experiments in ques- 

 tion such wires, maintained at a temperature of —78° C, were 

 extended until they broke ; it was then observed that the 

 fracture, instead of showing a contraction to a symmetrical 

 point, as is usual with other metals, had a flattened form,, 

 contraction having taken place in one azimuth only. This 

 may be referred to as a chisel-edge fracture. Soon after I 

 had made this observation Mr. B. B. Baker, working in the 

 same laboratory,, informed me that he had noticed a similar 

 phenomenon in some sodium wires on which he was experi- 

 menting, accompanied by semicircular markings of great 

 regularity t- I therefore examined the mercury wires for 

 these markings, and was able to observe them easily with a 

 lens magnifying a few times. A photograph of a portion of 

 a mercury wire showing the markings, magnified about five 

 times, is given in PI. XIII. fig. 1. T had previously observed 

 that both tin and lead wires (a very pure specimen) showed 

 marked roughenings of the previously smooth surface of the 

 wire on extension ; the markings seemed to have some regu- 

 larity. After carefully annealing the lead and tin wires at 

 temperatures near their respective melting-points for some 

 hours I obtained, on stretching the wires, the semicircular 

 markings with great distinctness for tin (fig. 2), and fairlv 

 well marked for lead (fig. 3). The photographs for ihe 

 lead and tin were taken with a magnification of ten times: 

 that of the lead shows the broken end of the wire. Fig, 4 

 shows the markings for tin magnified about 130 times. 



The wires exhibiting the markings show the one-siuYvi 

 contraction not only at the fracture, but throughout the 



* Communicated by Prof. A. W. Poiter, F.K.S. 



f See B. B. Baker, Pro cee dings of the London Physical Society, 1913. 



Phil. Mag. S. 6. Vol. 27. No. 161. May 1914. 3 M 



