AMMONIA. 



363 



a little, so that the renewal is continually proceeding. The gas liquifies 

 under a pressure of six atmospheres, at a temperature of 10 Cent. This 

 experiment can be artificially performed by heating chloride of silver satu- 

 rated with ammonia, and the silver will part with the gas at a temperature 

 of 40 C. The gas will then condense in a liquid form in the tube. The 

 experiment may be facilitated by placing the other extremity of the tube in 



snow and salt, and by the liquid we can obtain intense cold. This expe- 

 riment has been made use of by M. Carre in his refrigerator (which was 

 described in the Physics' section), by which he freezes water. We may, 



. 357. Generation of ammonia. 



however, just refer to the process. Whenever the condition of a body is 

 changed from that of liquid to a gas, the temperature is greatly lowered, 

 because the heat becomes " latent." The latest freezing machine consists of 

 an apparatus as shown in the illustrations herewith (figs. 359 and 360). The 

 machine is of wrought iron, and contains, when ready for action, a saturated 



