Chemistry and Physios. 313 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Sensitiveness of Selenium and Sxdphur to Light. — The 

 remarkable property possessed by selenium of having its electri- 

 cal resistance varied by the action of light has been the subject 

 of many investigations, since its first announcement in 1873. The 

 cause of this phenomenon is discussed by Shelfobd Bidwell in 

 a recent number of the Philosphical Magazine (August, 1885, pp. 

 178-191). Remarking upon the ingenious method of forming 

 selenium cells described by C. E. Fritts, who melted the selenium 

 as a thin film on a plate of metal with which it forms a sort of 

 chemical combination, he suggests the similarity of some of the 

 phenomena described by Fritts to those of electrolysis. The 

 arrangement of the two metallic plates with the third substance 

 between them, that is, of the selenium between the metal plate 

 upon which it is melted and the gold leaf film by which it is 

 covered, is suggestive of this; while the unequal resistance of the 

 two surfaces and the generation of an independent electromotive 

 force, in conjunction with the polarization effects observed, make 

 the conduction of selenium seem truly electrolytic. The objec- 

 tion that the selenium itself is not a electrolyte is met by the 

 suggestion that in the process of making the cell a metallic selenide 

 may have been formed, and the apparently improved conductivity 

 of the selenium, and the accompanying phenomena, may be ac- 

 counted for by the existence of this selenide, rather than by any 

 change in the crystalline condition of the selenium. 



As bearing upon ■ this question the author made a series of 

 experiments with sulphur. Five parts of sublimed sulphur and 

 one of precipitated silver were heated together, and a cell con- 

 structed by spreading some of the melted sulphur, containing 

 particles of silver sulphide, evenly over a surface of mica, and 

 then laying a piece of thin silver-foil on its surface. The cell 

 was found to vary in resistance to a marked degree when exposed 

 to the light of a burning magnesium wire. Other experiments 

 went to show the same result and to prove that the effect of the 

 light was due to the action of radiation proper and not to any 

 incidental rise in* temperature. Other cells, constructed in a 

 somewhat different manner, behaved in the same manner though 

 in different degrees; with all the resistance diminished to a 

 marked extent under the action of radiation. One of them, the 

 resistance of which was small, was connected with ten Leclanche 

 cells and a telephone, and exposed to a rapidly interrupted beam 

 of light; it gave a musical note nearly as loud as would be 

 obtained from a good selenium cell. All of the sulphur cells 

 resembled selenium in giving polarization-currents after being 

 detached from the battery. The author urges that the effects of 

 radiation, in the case of the sulphur-silver cell, are to be looked 



Am. Jour. Scl— Third Series, Yol. XXX, No. 178.— Oct., 1885. 

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