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III. 



OX THE ELECTETFICATIOX OF PHOSPHORUS SMOKE XrCLET. 



By JOHX J. DOWLIXG, M.A., F.Isst.P.; 



C. J. HAUGHEY, M.Sc. 



Read Deckubee 12, 1921. Published Febkhaby 24, 1922. 



I. — In the course of other work on the ionisation due to phosphorus, 

 one of us (H.) observed the following phenomenon : — 



A fragment of phosphorus, mounted between two vertical metal plates 

 under a bell-jar, gave rise to a fine vertical thread of smoke. On establishing 

 an electric field between the metal plates, it was observed that the smoke 

 thread divided into two ; each starting from a separate little smoke cap on 

 opposite ends of the phosphorus, and curving over towards the nearer plate. 



This clearly indicated that the smoke particles were electricallj charged : 

 some positively, others negatively. "We were struck by the remarkable fine- 

 ness of both smoke threads, having rather expected that a difiiise, fan-lil^e 

 structure should have resulted. We concluded that the smoke nuclei must 

 be of very unifonn si^e, and that each carried the same electric charge. 



II. — A wire gauze cage was now placed over the phosphorus, and 

 the obsei'vations repeated. Even with the largest available field 300 volts 

 per cm.) there was no noticeable sub-di\Tsion of the original vertical smoke 

 thread. It appeared that the particles became charged in tlie previous case 

 by what we may style a "water-dropper" action, without insisting on the 

 exact modus operandi. It seemed likely that interesting resrdts might be 

 forthcoming from a detailed examination of the phenomenon, and the follow- 

 ing is an account of the investigations carried out. 



III. — In the experunents just described the smoke thread is carried 

 upwards by a slight vertical convection current, maintained probably by the 

 heat of the smouldering phosphorus. At the same time the charged smoke 

 particles ai-e urged in a horizontal direction by the electric field. The height 

 (Ji) reached before the smoke strikes the plate varies inversely with tlie 



