On the Stretching and Breaking of Sodium and Potassium

Abstract

The author described how wires made of metallic sodium and potassium collapse when stretched, not to a point, as is the case with most plastic substances, but from two opposite sides only, into a chisel end. The wires upon which experiments were conducted were made in two ways - firstly, by pressing the metal through a small hole into a bath of paraffin oil to hinder oxidation; and, secondly, by running the metal, molten under oil, into a glass tube and allowing it to solidify. Wires made by both the above methods showed the same behaviour on stretching. Wires made by the second process also showed, on extension, two sets of equidistant rings on their surface, each inclined at an angle of 45 deg. to the axis, the rings of opposite sets touching along the line of greatest thinning and bisecting one another along the line at which no thinning takes place. Dr. Andrade has also noticed the same effects of breaking and forming rings with wires made of solid mercury. The author suggested an explanation of the phenomenon, based on the assumption that the portions of the metal brought into play are in the form of cubes. Such cubes when placed so that a plane through two opposite edges was parallel to the axis of the wire would allow of lateral contraction by faces sliding over one another in one direction only and not in the direction at right angles.