344 REFRIGERATION. 



be reflected upon the thermometer, the mercury 

 rose to the temperature of the surrounding me- 

 dium. The degree of cold, in another experi- 

 ment, was increased, by pouring upon the snow 

 some nitric acid; the consequence of which 

 was, that the mercury in the thermometer, 

 which was exposed to the focal point, sunk six 

 degrees lower than before. 



Mr. WALKER, who spent much time in pro- 

 secuting experiments, with a view of ascertain- 

 ing the greatest quantity of cold, that could be 

 Artificially produced, found, that by mixing two 

 parts of concentrated nitrous acid, by weight, 

 and one part of water, and by adding to this 

 mixture, when cooled to the temperature of the 

 atmosphere, of Glauber salt* Ibiss. and of 

 sal ammoniac, Ibiss. I say, that on adding the 

 Glauber salt to the nitrous acid, the thermome- 

 ter fell 52 degrees ; that is, from 50, which it 

 was at before, down to 1 ; and on adding the 

 sal ammoniac, it sunk to 9 below r 0. By these 

 means, Mr. Walker was enabled to freeze 

 quicksilver, at the time when the mercury was 

 at 45. in the air. 



The union of sulphuric acid, of spirit of wine, 

 and various other substances, with snow, will 

 produce a low temperature to an intense degree* 

 and by a proper management of artificial means, 

 ice may be formed for the luxury of man, in 



