Ort the Produilion of artificial Co! J. 277 



In the above table, the ordinary effe£i of fnow, or ice-powder, is given ; but, if the 

 latter be prepared (ground) with a (harp inftrument, ufing light preflure, the effedl will be 

 fomewhat greater, the ice being then reduced to an impalpable powder : hence, ice powder, 

 thus obtained from a block of ice, may at any time be fubftituted for fnow. 



Cold is produced by mixing various other chemical fubftances with ice : in the above 

 table, fuch only are retained as produce that effe£l in a remarkable degree. 



As the new nomenclature is now generally adopted, I have ufed it in this paper. 



POSTSRIPT. 



In the courfe of my former papers on the fubjedl of cold, I have had occafion to make, 

 incidentally, fome remarks on the power of water, under certain circumftances, in refill- 

 ing an extraordinary degree of cold without freezing ; likewife on the particular kind of 

 agitation which induces water, cooled below its freezing point, to cryftallize or become 

 ice. f As thefe are fubjefts which have likewife engaged the attention of others, I fhall 

 take the liberty of barely mentioning a fadl, having relation to thofe points, which has 

 lately occurred to me. 



It is a remarkable circumftance refpefting artificial freezing, that the ice thus procured 

 in the ufual way, (viz. by immerfing the water to be frozen, in a convenient veflel, in a 

 frigorific mixture,) will always be more or lefs opake, never tranfparent : this I had con- 

 ftantly remarked, without much attending to it ; however, having in the courfe of laft fum- 

 mcr been induced to try the efFeft of an ice-fpeculum for producing heat, it became neceflary 

 that the ice, which in this inflance was fubftituted for glafs, fliould be perfeftly tranfparent. 

 After varying the procefs in every poffible way I could think of, by immerfing tie -water to 

 be frozen, without effe£l;, I at laft fucceeded completely, by forming a coating of ice, of 

 fufficient thicknefs, on the outfide of a veflel containing the frigorific mixture ; the bottom 

 of this veflel, which was made concave for this particular purpofe, being immerfed for a 

 fufficient length of time in a (hallow pan of water. 



Hence arifes the means, before unknown to me, of obtaining ice, either in an opake, or 

 pcrfe£lly tranfparent ftate j moreover, water, as I have experienced lately, conftantly forms 

 a coating of ice on the outfide of a veflel containing a frigorific mixture, fo foon as it is 

 cooled to + 32°. 



* Phil. Tranf. for HSS, page tOl. 



Scientific 



