by Artificial CoIJ. 83 



Vey to any one a complete idea of the arrangement, as it ex- 

 hibits the retort containing the mercury, furrounded by the 

 cooling-mixture in the half-piut cup, which is infulated by 

 means of the corks, and prevented from coming in contact 

 with the ftone-ware jar— the fpcce between the latter being 

 occupied only with cold air, preferved in that ftate by means 

 of the frio-orific mixture in the exterior vefiel, and which 

 furrounds the jar. 



Fig. a reprefents the apparatus employed in the large ex- 

 periment, which is fimilar in its arrangement to the former 5 

 only that the cold atmofphere round the japanned pail had 

 no exterior cold mixture t> defend it; which, however, was 

 the lefs neceffary, as jhe earthen pan was of confiderable 

 thicknefs, and had acquired the temnerature of the mixture 

 that had been employed in cooling the 5 lib. of muriat of 

 lime. 



In experiments of the kind I have deferibed, all the ex- 

 terior veffels fhould be of earthen-ware or wood, which being 

 bad conductors of heat, prevent the ingredients from re- 

 ceiving heat from the atmofphere and furrounding objects 

 with the fame facility that they would through metals; and, 

 for a fimilar reafon, the interior veffels are bed of metal *, 

 that they may allow the heat to pafs more readily from the 

 fubftance to be cooled into the frigonlic mixture employed 

 for that purpole. 



Muriat of lime is certainly the moft powerful, and at the 

 fame time the mod economical fubftance that can be em- 

 ployed for producing artificial cold ; for its firft coftis a mere 

 trifle, being a rcfiduum from, many chemical procefTes, as 

 the diftillation of pure ammonia, &c. and often throwa 

 away : bclides, it may be repeatedly ufed for fimilar experi- 

 ments, nothing being necetiary for this purpofe but filtra- 

 tion and evaporation to bring it to its rirft fiate* The eva- 



• When we ufed a gl;ifs-rctort to contain the mercury, it was that we 

 might U- able to ice l'uch phenomena at mi^ht prcfent themfcives during 

 its congelation. 



Q % poration 



