924 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



culties in the way of pumping ammonia gas liad led liim to resort by 

 preference to another agent, patented simultaneously, \iz, methylic ether. 

 Professor Barnard says : " Gaseous ammonia is reduced to the liquid form 

 by pressure; but at 20° C. (08° Fahr.) it requires a pressure of not less 

 than eight and a half atmospheres to produce liquefaction, and at 25° 

 C. (77° Fahr.) not less than ten. Thus the pressure required rises very 

 rapidly with the temperature. On the other hand, to liquefy ammonia by 

 cold merely, under the ordinary atmospheric pressure, requires a reduc- 

 tion of temperature down to 38°.5 below zero of the Centigrade ther- 

 mometer. Ammonia, therefore, evaporates very rapidly even at tem- 

 peratures extremely low ; and as the latent heat of its vapor is great, 

 being estimated at 514° C, it may be used as a powerful means of pro- 

 ducing cold, provided any practicable method can be devised for remov- 

 ing the vapor as it is formed. To do this mechanically would require a 

 pump of large dimensions ; and inasmuch as considerations of economy 

 as well as of health and the comfort of the ox)erators would require 

 that the vapor should be reduced by comj)ression to the liquid state, 

 the pump should be capable of exerting a pressure of from seven to ten 

 atmospheres. If, therefore, it tvere only by mechanical means that ammonia 

 could be condensed, this substance could not be projitably used as a means 

 of producing coldP 



To show what at that time was meant by liquid ammonia, and the views 

 Professor Barnard entertained of the unequalled value of ammonia vapor 

 for the abstraction of heat, I have another passage to quote. He says : 

 "It may thus be stated that the latent heat of a kilogram of liquid 

 ammonia is equal to ninety calories. * The latent heat of a kilogram of 

 its vapor, that is to say, of ammoniacal gas, amounts to five hundred 

 and fourteen calories. The latent heat of water, liberated in the act of 

 congelation, is equal to seventy-nine calories per kilogram ; so that one 

 kilogram of ammonia would be capable by its evaporation of freezing 

 six and one-half kilograms of water taken at the initial temperature of 

 zero, or five kilograms taken at the temperature of 24° 0. (75°.2 Fahr.)." 



Alcohol absorbs ammonia readily. Messrs. Eoscoe and Schorlemmer, in 

 their admirable Treatise on Chemistry, furnish the following illustration 

 and remarks :t "The condensation of ammonia by pressure and the i^ro- 

 duction of cold by its evaporation can easily be shown by the following 

 experiment: The ai)i:»aratus required for this purpose consists essen- 

 tially of two strong glass tubes {a and b), which are closed below and 

 are connected together by the tubes (c c) and {d d). The tube {d d) ends 

 at (I) in a nari'ower tube (m m), which is at this point melted into a tube 

 («). The tube («) is three-fourths filled with an alcoholic solution of 

 ammonia saturated at 8°, and then i)laced in the cylinder (A). The 

 syphon-tube {(j) and the tube (//), which reach to the bottom of the 



*A French calorie sigjiifies tho aniouut of licat required to raise tlie temperature of 

 a kilogram of ^ater, taken at 0° C. of temperature, 1° C, aud this is adopted as a unit, 

 tl am indebted to Messrs. D. Axjpleton & Co. for the use of this cut. 



