512 Mr Varley, On the Absorption of 



Air. 



To test if any absorption of the light in air could be detected 

 the photo-electric currents were measured (1) when the interposed 

 vessel was filled with air at atmospheric pressure, and (2) when it 

 was exhausted to a pressure of 15 mms. of mercury by means 

 of a water pump, the actual pressure being read on a suitable 

 manometer. 



No appreciable difference in the intensity of the light could be 

 detected, the mean value obtained for the current (in arbitrary 

 units, viz. in electrometer scale divisions per 10 sees, illumination) 

 being in the first case 152'0, and in the second case 152"7 (means 

 of 10 readings). 



Air having shown no absorption the intensity of the light 

 in dealing with other gases was measured (1) when the interposed 

 vessel was filled with air, and (2) when it was filled with the gas 

 under examination. 



Carbon Dioxide. 



Carbon dioxide, prepared from marble and hydrochloric acid, 

 washed by bubbling through water, and dried over calcium 

 chloride, also showed no absorption of the ultra-violet light, 

 the mean values of the photo-electric currents obtained, when 

 the vessel was filled with air and carbon dioxide being 88'0 and 

 87*9 respectively. 



Carbon Monoxide. 



The carbon monoxide was prepared from sodium formate and 

 strong sulphuric acid, washed by caustic soda solution and dried 

 over calcium chloride. 



Mean value of current when vessel filled with air = 191 3 

 „ „ „ „ „ CO = 178*7 



giving an absorption of the light in passing through a length 

 of 10 cms. of carbon monoxide at atmospheric pressure of 6*5 °/ . 



In another experiment the carbon monoxide was prepared 

 from potassium oxalate and strong sulphuric acid, the carbon 

 dioxide being removed by passing the gas through a strong 

 solution of potash. A slightly lower value for the percentage 

 absorption was obtained, doubtless owing to the imperfect removal 

 of the dioxide. 



Marsh Gas. 



The marsh gas was prepared in the usual manner by heating 

 strongly a mixture of one part of sodium acetate with four parts 



