PAPERS OX CHEMISTRY AND PHYSICS 281 



THE ACTIOX OF LIGHT UPON AESEXIC TRI- 

 SrLFIDE HYDEOSOL 



Eay V. MuEPHY. Illinois Wesleyax Uxh-frsity 



In the course of some experimeiits upon the coudiictiv- 

 ity of mixtures of electrolytes and colloids it ^vas ob- 

 served that the conductivity of a carefully prepared 

 arsenic trisulfide hydrosol was gradually increasing, 

 the increase being most pronounced during those periods 

 when the lamp of the thennostat remained lighted. It 

 was finally decided that the heating lamp was the source 

 of the disturbance, the reaction in the sol being a photo- 

 chemical one. Tests were made by exposing some of 

 the sol in the conductivity cell to the light of a 500 watt, 

 nitrogen-filled lamp placed about 60 cm. from the cell. 

 A marked increase in the conductivity resulted. The 

 investigation was then extended to a study of the change 

 in the conductivity of the sol of various dilutions when 

 exposed to the light of the lamp under uniform conditions 

 of temperature and intensity of illumination. 



Pkepaeatiox of the Sol 



One liter of a solution of H^S, prepared by saturation 

 of ice-cold freshly boiled distUled water, was added 

 slowly, with constant stirring, to one liter of AS2O3 solu- 

 tion containing two gi*ams AS2O3. The resulting clear 

 sol was then boiled for about six hours to remove excess 

 HoS, the boiling being done in a darkened room. A por- 

 tion of the water was allowed to evaporate until a sol 

 containing about 4.5 grams AS2S3 per liter was obtained. 

 The resulting sol was faintly milky by reflected light, but 

 clear by transmitted light. It was allowed to stand 48 

 hours. This is taken as the ''100% sol". Samples con- 

 taining 75fc, 50%, 25%, 12.5% and 5% of the original 

 sol were also prepared by dilution of the 100% sol with 

 "conductivity" water of specific conductivity 1.1 x 10^. 

 All samples were allowed to stand two weeks to age be- 

 fore the studies were made. 



