142 THE ROYAL SOCIETY OF CANADA 



theory that neutral atomic chlorine should have a similarly transparent 

 region, shifted slightly towards the infra-red on account of the smaller 

 mass of the chlorine nucleus. Molecular chlorine has some well- 

 known absorption bands in the visible region and it would be very 

 interesting to see if these bands could be made to disappear by the 

 disruption of the chlorine molecules into atoms. Further research 

 is needed to determine this point. 



1 1 . Experiments with Ionized A rgon 



(a) The absorption tube consisted of a quartz tube 40.3 cm. 

 long and 1.5 cm. in diameter, having clear quartz windows fused in 

 at each end and two side tubes in which discharge terminals were 

 sealed. The argon used was obtained as before by repeatedly passing 

 a mixture of 80 per cent, argon and 20 per cent, nitrogen over turnings 

 of calcium metal maintained at a temperature of 600°C. The ab- 

 sorption tube was thoroughly exhausted and then filled with purified 

 argon gas at a pressure of 2 mm. of mercury. The light from the 

 electric spark between aluminium terminals under distilled water^ 

 was focussed on the slit of the large quartz spectrograph used in the 

 previous experiment and the absorption tube was placed in the path 

 of the light between the focussing lens and the spectrograph slit. 

 The gas in the absorption tube was feebly ionized by passing a weak 

 discharge from a four volt induction coil between the discharge 

 terminals in the side tubes. With the absorbing column of gas in 

 this ionized condition the light from the discharge between the 

 aluminium terminals under water was passed through the tube into 

 the spectrograph and allowed to fall upon a Wratten panchromatic 

 plate for one a:nd three-quarters hours. The aluminium spark under 

 water gave a beautifully continuous spectrum between the wave- 

 lengths X = 7000 A.U. and X = 2150 A.U., but there was no evidence 

 of any absorption whatever due to the ionized argon. 



The experiment w'as repeated using as a source of radiation the 

 blue argon discharge produced by passing the discharge from a 

 condenser through an argon Geissler tube made of quartz. If the 

 blue spectrum is due to a disturbance of electrons in the singly ionized 

 atom, then argon gas, when feebly ionized, should be in a condition 

 to absorb this blue radiation. The gas in the absorption tube was 

 excited as before by a very weak discharge, so that it was in a feebly 

 ionized condition. The time of exposure was one hour and forty 

 minutes, but there was no indication of any absorption of the blue 

 radiation. 



'Henri, Phys. Zeit., No. 12, p. 516, June 15, 1913. 



