34 



2^th March, i ! 



Joseph J. Murphy, Esq., in the Chair. 



J. Brown, Esq., read a Paper on 

 FORMATION OF A STALACTITE BY VAPOUR. 



The reader described a curious phenomenon which he had 

 observed during the electrolysis of the double chloride of 

 aluminium and sodium fused in a small porcelain crucible 

 provided with a porous partition. The anode was of carbon, 

 and the cathode platinum-foil. 



A considerable quantity of vapour was given off, especially 

 from about the anode, forming a white smoke and depositing a 

 white substance, doubtless mainly hydrated aluminium chloride, 

 on the carbon rod, and about the mouth of the crucible, 

 ultimately closing up the latter all but a small hole, through 

 which the vapour poured rapidly. From this hole there grew 

 out a beautifully delicate little tube about i^- inch long, and 

 tapering from about | inch at the base to T V inch in the middle 

 of its length, after which it increased in diameter, and also 

 flattened out owing to the vapour-jet coming close over the 

 bend of the platinum-foil cathode, which seemed to cause, by 

 some kind of eddy current, a flattening of the stream of vapour. 



Soon afterwards the supply of vapour slackened, and there 

 was a corresponding diminution in the size of the tube in the 

 last quarter-inch of its length till the end became almost closed. 

 The formation of this tube seems quite analogous to that of the 

 ordinary tubular lime-carbonate stalactite deposited from drop- 

 ping water by contact with the atmosphere ; only we have here 

 a tubular deposit of hydrated aluminium chloride by the 

 combination, at the edge of the growing tube, of the water- 

 vapour in the air with the anhydrous chloride contained in the 

 vapour-stream, 



