8 DR. EDWARD C. EDGAR ON THE ATOMIC WEIGHT OF CHLORINE. 



to 250 C. Then hydrogen was cautiously admitted through the tap / until the 

 pressure shown by the manometer P was nearly atmospheric, at which point I was 



temporarily closed. 



The glass cul-de-sac H was broken by lifting the small piece of steel rod G, 

 imbedded in glass, by means of an electromagnet, and allowing it to drop. Since the 

 temperature of the liquid chlorine was about -25 C., the pressure on the reversed 

 tap e was rather more than atmospheric. The ignition of chlorine at the tip of the 

 quartz jet F was brought about by cautiously turning the tap e so as to admit chlorine 

 to F, at the same time rapidly passing sparks between the platinum tips until the 

 gas had lit. Chlorine burns in dry hydrogen with a fine needle-shaped flame. In 

 daylight this cannot easily be seen ; the combustion therefore was carried out in a 

 dark room. The only part of the combustion vessel A heated by the burnt gases 

 was the end immediately opposite the flame ; during the combustion this was 

 continuously cooled by a. rapid stream of water. The atmosphere of hydrogen was 

 continually renewed from L, while the tap c controlled the admission of chlorine to 

 the jet. The elongation of the chlorine flame showed when the atmosphere was 

 failing, but the readings of the manometer P were chiefly relied on in following the 

 changes of pressure of the hydrogen. 



During the combustion the endeavour was made so to regulate the admission of 

 hydrogen as to keep it at a pressure just below atmospheric, but more often than not 

 the attempt failed, owing to the rapid rate at which the gases burnt and the small 

 size of the combustion vessel. If the flame went out, the hydrogen atmosphere had 

 to be restored and the chlorine re-lit by a spark, but this seldom occurred during the 

 experiments. 



The hydrogen chloride, immediately after its formation in the flame, was condensed 

 as a pure white solid by the liquid air surrounding the lower end of the vertical limb 

 B ; some chlorine, too, which had escaped burning in the flame, was condensed along 

 with the hydrogen chloride. As the solid accumulated, the liquid-air vessel was 

 gradually raised so that, at the end of the combustion, nearly the whole of B was 

 immersed in liquid air. 



The combustion was continued until only a few grammes of liquid chlorine were 

 left in E, when the tap / of the palladium bulb was finally closed and L allowed to 

 cool. The flame was now made very small. As the atmosphere became rarefied, the 

 flame became more and more attenuated until, just before it went out,*e was finally 

 closed. The combustion, the average duration of which was over four hours, was then 

 at an end. 



Then the residual gases in the vessel were sucked out by the pump through m, 

 collected and subsequently analysed. The vapour pressures of solid hydrogen chloride 

 and solid chlorine at the temperature of liquid air were so exceedingly small that 

 none could be detected in the gases pumped out. In the gas analysis it was assumed 

 that both these gases were absent. Even in the highest vacuum obtainable under 



