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



pump and weighed. It was then attached to the rest of the apparatus by a ground- 

 glass joint. 



The evaporation of the solid hydrogen chloride in B and its passage through Q was 



conducted as before, though at a lower pressure. 



The purified hydrogen chloride passed through the taps z and y into the bulb Y, 

 surrounded at first by cold water, later by a calcium-chloride-and-ice freezing 

 mixture. Here the gas was absorbed; occasional shaking of Y kept down the 

 pressure. Towards the end of the absorption, when only a very little solid hydrogen 

 chloride was left in B (fig. 3), the tap y was closed and the end of the thick-walled 

 capillary tube Z was immersed in liquid air. The last traces of hydrogen chloride 

 condensed here. Preliminary experiments showed that in a high vacuum no 

 measurable amount of hydrogen chloride could cling to the walls of the quartz 

 combustion vessel. As an extra precaution, however, the walls of A were always 

 warmed by hot water during the last stages of the condensation of hydrogen chloride. 



Z was separated by fusion from Y, but was afterwards weighed along with it. 

 Finally, the different parts of the whole apparatus were disconnected as before. 



9. Analysis of Residual Gases. The analysis of the residual gases was carried out 



as follows : 



Fi" 1 . 8 is a sketch of the apparatus in which the gases were collected. It consisted 



of a graduated glass reservoir A furnished with two taps, B and C, and connected with 



a graduated tube I). The weight of the apparatus, filled with 

 mercury between the taps B and C, having been determined, 

 D was filled with mercury and the whole placed in a mercury 

 trough. The gases were collected in D and passed into A ; 

 it was assumed they were hydrogen and nitrogen. 



The gas apparatus, standing in the trough, was then taken 

 to the balance room. The tap C was opened and the whole 

 allowed to reach the temperature of the room. By noting 

 the difference in level of the mercury in A and of the 

 mercury in the trough, with the aid of the etched scales on 

 A and D, the divisions of which were 1 mm. apart, and by 

 subtracting this difference from the barometric height the 

 pressure of the gases was found. The tap C was closed, the 

 tube D emptied, and the gas apparatus was again weighed. 



The difference in the weights of the apparatus before and after the collection of the 



residual gases (corrected for the weight of these residual gases) gave their volume 



under the ascertained conditions of temperature and pressure. 



D having been refilled with mercury, the gas apparatus was replaced in the trough, 



C was opened, and successive small volumes of pure, dry oxygen added to the gases. 



Between each addition C was closed and the platinum spiral in A was cautiously heated 



by an electric current so as to bring about the combination without explosion of all 



Fig. 8. 



