ON THE ATOMIC WEIGHT OF CHLOEINE. 175 



The palladium was raised to a very low red heat and the apparatus on the right-hand 

 side of the tap C evacuated, arid then allowed to cool to the ordinary temperature. 

 The tap C was cautiously opened, the electrolysis resumed, and hydrogen admitted to 

 the palladium until it was saturated, care being taken that the pressure on the left- 

 hand side of the tap C was always kept slightly above the atmospheric. This last 

 precaution was easily effected by opening the tap D fully and regulating the admission 

 of the gas to the palladium by means of the tap C. C was now closed, the temperature 

 raised to a very low red heat, and the evolved gas sucked out by the pump. The 

 operation of alternately filling the palladium with hydrogen and evacuating the bulb 

 at a high temperature was repeated four times, when it was considered that all traces 

 of nitrogen or other gases had been removed from the palladium bulb and the 

 connecting tubes on the right-hand side of C. The palladium after the final 

 exhaustion was maintained at a low red heat whilst hydrogen was admitted to it 

 through C. 



When the pressure throughout the apparatus had become a little more than 

 atmospheric this was easily attained by so adjusting the tap H of the electrolysis 

 tube that the rate of escape of the evolved oxygen through it was slightly less than 

 its actual rate of evolution the tap B was slightly opened and the current of 

 hydrogen was passed through the palladium, the gas finally escaping through a 

 capillary tube dipping under mercury. The palladium was now allowed to cool very 

 slowly, the current of hydrogen passing through it all the time. Great care was 

 taken that the rate of entry of hydrogen to the palladium was always greater than 

 its rate of occlusion, or, in other words, that an excess of hydrogen was constantly 

 escaping through the capillary tubing during the occlusion. 



At the temperature of maximum absorption of hydrogen from 07 to 100 C., the 

 cooling of the palladium was interrupted and the temperature kept constant for 

 one hour. The cooling was then allowed to continue, hydrogen passing through the 

 apparatus all the while, until the temperature of the room was reached. The 

 taps B, C, D, and H were then finally closed and the electrolysis discontinued. The 

 palladium bulb was fused off from the rest of the apparatus, the outside cleaned and 

 dried, and the whole was then ready for weighing. 



2. The Palladium Bull}. 



The palladium vessel A (fig. 2) was a bulb of hard Jena glass of about 180 cub. 

 centims. capacity, fitted on the one side with a tap B, the inner portion of a ground 

 glass joint M, and a glass jet J, at which the combustion of hydrogen in chlorine 

 was carried out ; and on the other with a capillary tube by which it could be 

 attached to the rest of the hydrogen apparatus and afterwards separated by fusion 

 with the blowpipe flame. 



Since the date when Professor E. W. MOELEY defined a tap as "a contrivance for 



