Cn a veil.' Mode of Artificial Congelallon. 417 



therefore expanded, the water is gradually squeezed up through 

 the orifice, and forms bv congelation a regular pyraniid, rising 

 by successive steps ; or, if the projecting force be greater, and 

 the hole more contracted, it will dart off like a pillar. The ra- 

 diating or feathered lines which at first mark the frozen surface, 

 are only the edges of very thin plates of ice, implanted at deter- 

 minate angles^ but each parcel composed of parallel planes. 

 'I'his internal formation appears very conspicuous in the con- 

 SJeuled mass which has l)een removed from a metallic cup, be- 

 fore it is encirelv consolidated. — Sea water will freeze with al- 

 tiiost e(jual ease ; but it forms an incompact ice like congealed 

 syrup, or what is commonly called water-ice. 



When cups of glass or metal are used, the cold excited at the 

 open surface of the liquid extends its influence gradually down- 

 wards. But if the water be exposed in a porous vessel, the pro- 

 cess of evaporation, then taking effect on ail sides, proceeds wilh 

 ;t nearly regular consolidation towards the centre of the mass, 

 thickening rrither faster at the bottom from its proximity co the 

 action of the absorbent, and leaving sometimes a reticulated 

 space near the middle of the upper surface, through which the 

 iiir3 disengaged by the progress of congelation^ makes its escape. 



Singular Modification of the Proceis. 



When verv feeble powers of refrigeration are employed, a most 

 singular and beautiful appearance is, in course of time, slowly 

 produced. If a pan of porous earthen-ware, from four to six 

 inches wide, be filled to the utmost with common water till it rise 

 above the lips, and planted above a dish of ten or twelve inches 

 diameter, containing a body of sulphuric acid, and then a broad 

 ro'jnd receiver placed over it ; on reducing the included air to 

 some limit between the twentieth and the fifth part of its usual 

 density, according to the coldness of the apartment, the liquid 

 mass will, in the space of an hour or two, become entwined with 

 icy shoots, which gradually enlarge and acquire more solidity, 

 but always leave the fabric loose and unfrozen below. The icy 

 crust which covers the rim, now receiving continual accessions 

 from beneath, rises perpendicularly by insensible degrees. From 

 each point on the rough surface of the vessel, filaments of ice, 

 like bundles of spun glass, are protruded, fed by the humidity 

 conveyed through its substance, and forming in their aggrega- 

 tion a fine silvery surface, analogous to that of fibrous gypsum or 

 satin-spar. At the same time, another similar growth, though 

 of less extent, takes place on the under side of the pan, so that 

 continuous icy threads might appear vertically to transpierce the 

 wi'.rc. The whole of the bottom becomes likewise covered over 

 witl> elegant icv foliations. Twenty or lliirty hours may be re- 



Vo!. 5 1 . .No. i» 12. June 1818. D d quired 



