4 IS On a new Mode of Artificial Congelation* 



quired to produce those singular effects ; but the upper body of 

 jee continues to rise for the space of several days, till it forins a 

 circular wall of near three inches in height, leaving an interior 

 grotto lined with fantastic groups of icicles. In the meanwhile 

 the exfoliations have disappeared from the under side, and the 

 outer incrustation is reduced, by the absorbing process, to a nar- 

 row ring. The icy wall now suffers a regular waste from e.xter- 

 nal erosion, and its fibrous structure becomes rounded and less 

 apparent. Of its altitude, however, it loses but little for some 

 time; and even a deposition of congealed films along its coping 

 or upper edge, seems to take place, at a certain stage of the 

 process. This curious effect is owing to a circumstance, which, 

 as it serves to explain some of the grand productions of natuie, 

 particularly the Icebergs of the Arctic Circle, merits particular 

 attention. The circular margin of the ice, being nearer the ac- 

 tion of the sulphuric acid than its inner cavity, must suffer, by 

 direct evaporation, a greater loss of heat ; and, consequently, 

 each portion of thin air that rises from the low cavity, being 

 chilled in passing over the colder ledge, must deposit a minute 

 corresponding share of its moisture, which instantly attaches it- 

 self and incrusts the ring. Whatever inequalities existed at first 

 iji the surface of the ice, will hence coiitiuually increase. 



Artificial Congelation lest performed on a large Scale. 

 Artificial congelation is always most commodiously perfornisd 

 on a large scale. Since the extreme of rarefaction is not wanted, 

 the air-pump employed in the process admits of being consider- 

 ably simplified, and rendered vastly more expeditious in its ope- 

 ration. Two or three minutes at most will be sufficient for pro- 

 curing the degree of exhaustion required, and the combined 

 powers of evaporation and absorption will afterwards gradually 

 produce their capital effect. In general, plates of about a foot 

 in diameter should be preferred, which can be connected at plea- 

 sure with the main body of the pump. The dish holding tha 

 sulphuric acid is nearly as wide as the flat receiver: and a set 

 of evaporating pans belongs to it, of different sizes, from seven 

 to three inches in diameter, which are severally to be used ac- 

 cording to circumstances. The largest pan is employed in the 

 cold season, and the smaller ones may be successively taken as 

 the season becomes sultry. On the whole, it is better not to 

 overstrain the operation, and rather to divide the water under 

 different receivers, if unusual powers of refrigeration should be 

 required. As soon as the air is partly extracted from one re- 

 ceiver, the communication is immediately stopped with the bar- 

 rel of the pump, aud the process of exhaustion is repeated oa 

 another. In this way, any number of receivers, it is evident, 



may 



