by Artificial Cold. ?? 



tffih, &c. and latterly Walker, who, in his treatife on that 

 fubjecf, feemed to have exhaufted the whole train of mix- 

 tures, and certainly has (hewn confiderable ingenuity in the 

 contrivance of the inftruments and apparatus he employed to 

 accompli fli the end he had in view: but, though I am pof- 

 letfed of the principal part of them, and repeated his expe- 

 riments with the greateft care and attention, I cannot fay I 

 fucceeded in all of them. The materials employed by Seguinc 

 for frigorific mixtures are certainly the beft that have yet 

 been propofed, or perhaps can poflibly be deviled. Con(i- 

 ilering the muriats as a clafs of falts beft fuited for the pur- 

 pofe, and having tried them all, he gave the decided prefer- 

 ence to muriat of lime in cryftals. His method was to mix 

 the cryftals, previoufly pulverifed, with an equal weight of 

 uncomprefled fnow. My friends Allen and Lawfon were, I 

 believe, the firft who in this country tried that method : 

 this was in December laft; and they fucceeded perfectly iu 

 freezing the mercury. 



Determining to make the experiment with, accuracy in 

 refpect to the weight of the materials employed, and on fach 

 a fcale that it might be repeated by any one, on the 30th of 

 January laft we collected a quantity of fnow for the purpofe. 

 The temperature of the laboratory at the time was 40°. It 

 may not be improper to mention here, that the thermometer 

 employed in this and the other experiments which followed 

 was filled with tinged alkohol, and accurately divided ac- 

 cording to Fahr. fcale, as mercurial thermometers cannot be 

 reforted to for determining degrees of temperature at or un- 

 der the freezing point of that metal. Having put into an 

 earthen pan equal parts of muriat of lime of the temperature 

 of 40° and fnow at 32 above cf, we found that the tempe^ 

 raturc of the mixture, as foon as liquefaction took place, was 

 3a below o°. Into this mixture we iinmerfcd, each in fe- 

 parate veflels, 8 oz. troy of muriat of lime, and the fame 

 weight of fnow, by which means, and with very little trou- 

 ble, they were cooled down to 5 above o°, the mixture 



gaining 



