Mlf. O. W. RICHARDSON ON THE ION1SATION 



To CLCCTKOMCTCK 



8 centims. in length. The wire was heated electrically as before, and in measuring its 

 temperature the same Wheatstone's bridge method was made use of to determine its 

 resistance. This method is an exceedingly sensitive one, and there is no difficulty in 

 keeping the resistance constant to one or two degrees at the highest temperatures. 

 This is a matter of considerable importance in working with hot wires when the leak 

 is a rapidly variable function of the temperature. 



The whole of the apparatus, which was in electrical connection with the leads A, 

 was insulated on paraffin blocks and could be charged to any potential between and 

 800 volts. Owing to the heating current through the platinum filament there was 

 a fall of potential along the wire amounting to from about 2 to 6 volts according to 

 the temperature, which had to be taken into account at low voltages. The current 

 from the wire was measured by means of a Dolezalek electrometer with a suitable 



capacity attached to the quadrants. For insulating 

 the plate B the dry glass inside the tube was found to 

 be good enough, but outside it was protected by 

 sealing wax surrounded by a guard ring. 



In work of this kind the cleanliness and purity of 

 the materials employed are of the utmost importance. 

 In the apparatus shown in fig. 1 it will be noticed that 

 all the parts are of platinum and glass. This enabled 

 the tube to be cleaned with boiling nitric acid and 

 distilled water before the experiments commenced. 

 The ground-glass joint E enabled a further refinement 

 to be effected by obviating the necessity of finally 

 fusing the side tube on to the pump connections and 

 thereby bringing the cleaned wire into contact with 

 the gases from the blowpipe flame. The ground joint 

 was lubricated with carefully purified graphite and was sealed with mercury 

 externally. 



The oxygen used was prepared in two ways. When small quantities only were 

 required it was obtained by heating potassium permanganate in a tube sealed on to 

 the apparatus. It was found advisable to have the tube containing the per- 

 manganate shut off from the rest of the apparatus by a mercury trap as it gave 

 off a small quantity of gas or vapour even when the salt had been dried by heating 

 to 120 C. for two hours before it was sealed up. The oxygen produced in this way 

 is freed from dust by plugging up the front end of the permanganate tube with glass 

 wool. When larger amounts of oxygen were required the above method was found 

 to be inconvenient, and the electrolysis of concentrated caustic potash was substituted 

 for it. The oxygen evolved underwent a preliminary drying by passing through 

 a tube packed with solid potassium hydrate before being admitted, through a glass 

 tap, to the main apparatus, where it was subjected to the further action of phosphorus 



To PUMP ETC. 



Fig. 1. 



