On the analysis by positive rays of the heavier constituents of the atmosphere; of the gases in a vessel in which radium chloride had been stored for 13 Years, and of the gases given off by deflagrated metals

Abstract

Sir James Dewar was kind enough to supply me with large quantities of the residues obtained from the evaporation of many thousand tons of liquid air. These residues had been absorbed by charcoal which had been kept in a sealed vessel. I have analysed these residues by the Positive Ray Method. The general arrangements were the same as those described in my book on Positive Rays. Some alterations, however, were necessary, as I used for these investigations a much more powerful induction coil than the one I had hitherto employed. With this coil so much heat was developed in the part of the tube near the cathode that any wax joints in that neighbourhood, even though they were cooled by a water jacket, gave off enough gas to spoil the vacuum for positive ray purposes. To avoid this difficulty I substituted for the wax joint, which formed the connection between the glass bulb in which the discharge takes place and the brass vessel which contains the camera, a joint made by a method used by Mr. Roebuck, and described by him in the ‘Physical Review.' vol. 28, p. 264 (1909). The method consists in first making on the outside of the glass tube a deposit of platinum by one or other of the devices used for platinising glass, and then depositing slowly by electrolysis a layer of copper on the platinum. With care this layer can be made thick and firm enough to enable a brass tube connected with the camera vessel to be soldered on to it, and an air-tight joint obtained which does not give off gas when heated by the discharge. The method adopted to analyse the gas was to put some of the charcoal containing the gaseous residues into a small vessel A, which was fused on to the discharge tube B; there was a tap between A and B, and this was turned until B had been exhausted to a very low pressure; there was also a very fine capillary tube in the circuit between A and B, and when the pump used for exhausting the discharge tube was kept in action a continuous stream of gas from A could be kept flowing through the discharge tube without making the pressure too high to obtain good photographs. Just before the tap between A and B was opened a photograph was taken with ordinary air going through the discharge tube, and the lines in this were compared with those on the photograph obtained when the gas from A was flowing through the tube.