IOWA ACADEMY OF SCIENCE 
179 
THE EFFECT OF RUPTURE BY ABRASION ON THE ELECTRICAL 
CONDUCTIVITY OF SELENIUM.* 
BY F. C. BROWN. 
Sometime ago while filing away the surface of the selenium in a Giltay cell 
in order to find out directly certain limits on the depth of penetration of 
selenium by light**, I discovered a new effect. 
This effect of mechanical rupture on light-positive selenium resembles in a 
general way the many other well known effects in these varieties of selenium. 
Rupture produces an increase in the conductivity, but this increase is not 
permanent. The recovery is extremely slow, often requiring more than a 
month for the selenium to attain the electrical condition existing before rupture. 
The experiments are especially interesting because of their bearing on the 
dynamic equilibrium theory of light sensitive selenium.*** 
The three components of selenium exist in dynamic equilibrium in a sort of 
solid solution. But the equilibrium is constrained to act in certain regions 
or configurations. The rupture of the surface of the selenium necessarily 
destroys this configuration, and consequently the equilibrium condition. The 
restoration of the equilibrium condition reminds one of the restorative growth 
of crystals, such as is well known to occur when certain large crystals have been 
fractured or broken. 
The rupture mentioned has been produced by the author by filing and by 
Giltay by a sand blast. The method of procedure was to file away uniformly 
the surface of the selenium from between the wires of a Giltay cell. The 
selenium that was filed away was generally weighed in order to estimate the 
relation between the conductivity and the amount of selenium and also to 
ascertain the effect of continued filing. 
THE PRODUCTION OF THE RUPTURE. 
I shall first describe the method of production of the rupture which Mr. J. W. 
Giltay had the kindness to describe to me in a letter. His account reached me 
only a few days after I had completed my preliminary experiments on this 
subject, and while he does not give the dates of his experiments it is entirely 
possible that he discovered the phenomenon first. 
The rupture was produced by Giltay by a mild sand-blasting. The apparatus 
used by him is shown in Fig. 1, and is described in his own words as follows: 
“The sand falling apparatus consists of a square wooden tube, ending at the 
upper end with a conical piece and at the lower end in a box. In this box is 
placed a wooden frame in a slanting position as shown. This frame carries a 
net of wire on which the article to be sand blasted is placed. In the box is 
also placed a wooden drawer, of which two are required. One of these drawers 
*The results published in this paper were also published in the Physikalische 
Zutschupt under date of Nov. 15, 1912. 
**See paper in Phys. Rev. 34, p. 201, 1912. 
***See Phys. Rev. xxxiii p. 403. 
