412 Discharge of Electricity from Hot Platinum. 



of 312 of the units previously employed. After maintaining 

 the wire at this temperature for 52 minutes, the leak had 

 fallen to 7*5 units. On lowering the temperature to 610° C, 

 the leak fell to 1*3 units. With the wire at this temperature 

 the tap was turned and the phosphorus vapour admitted. 

 The leak was now determined as quickly as possible, and 

 found to he equal to 2175 units. Thus the phosphorus 

 vapour increased the leak from the hot wire to seven times 

 the value obtained from the wire when new, and to nearly 

 two thousand times the value it gave immediately before the 

 phosphorus was admitted. The phosphorus was now rapidly 

 heated to 200° C, when the leak from the wire was found to 

 have risen to 16,900 units, or more than fifty times the initial 

 leak from a new wire. Before any more readings could be 

 taken the wire broke. 



This effect of phosphorus on a hot platinum wire is of 

 especial interest as being one of the few instances where the 

 leak from that metal is affected in a definite and metrical 

 way by a foreign chemical substance. The above experiments 

 are not complete enough to determine the nature of the action 

 giving rise to the positive leak with absolute certainty, but there 

 are some points which are worthy of further consideration. For 

 instance, the results given in Table II. show that the effect 

 accumulates if a cold wire is left exposed to the vapour. This 

 might be due either to an absorption of the phosphorus by 

 the cold platinum, or to a gradual formation of an increasing 

 quantity of vapour inside the apparatus. In the latter case, 

 the falling-off with time at constant temperature would 

 probably be due to the gradual absorption of the vapour bv 

 the wire. But if the effect were proportional to the amount 

 of a vapour which gradually accumulated, we should expect 

 pumping to reduce it in the same ratio as it reduced the gas- 

 pressure. Pumping was found to reduce the effect slightly, 

 but not to this extent. For instance, in Table II. the pump 

 was worked twice between the readings for 6 and 9 minutes. 

 This corresponded to reducing the pressure to less than one 

 half ; but the corresponding fall in the leak was onlv equal 

 (proportionally) to that in the preceding interval of time, 

 when no pumping had been done. If the pumping had not 

 been done in the 6-9 minutes interval, the ratio of the final 

 to the initial leak would have been slightly greater than in 

 the preceding interval, owing to the rate of decay falling off 

 with time. Another wire which had been heated, in presence 

 of a pentoxide-bulb giving off phosphorus vapour, until the 

 leak ceased to fall away perceptibly with time, gave the fol- 

 lowing values of the leak after successive strokes of the pump, 



