SIR WILLIAM SIEMENS, F.R.S. 325 



climates in a sanitary point of view, and the time was not distant, 

 he thought, when houses and places of public resort would be re- 

 frigerated with the same care and regularity as they were now 

 heated when necessary. He believed this might be accomplished 

 at a cheap rate. It was stated in the paper, and it was an 

 undoubted scientific fact, that mechanical refrigeration might be 

 obtained at a cheaper rate if the reduction of temperature required 

 were only slight than if it were considerable. Thus, an air- 

 machine producing ice would work much less economically than 

 one producing only cool air. In order that the subject might be 

 more fully opened out for discussion, he proposed to refer shortly 

 to the different methods that had beeii devised for producing re- 

 frigeration. There were four methods in use. The first was the 

 old system by the evaporation of alcohol, ether, or other volatile 

 substances. Even water when allowed to evaporate under a 

 current of air produced refrigeration. Alcohol did so to a greater 

 extent, and ether to a still greater extent. This method had been 

 adopted, perhaps, for centuries ; but in recent times it had been 

 improved by Siebe and by Harrison, who had contrived that the 

 vapour produced by evaporation should not be lost, but that it 

 should be mechanically compressed and condensed, in order to 

 serve over and over again. The method of producing the reduced 

 temperature was the same in both cases, but instead of losing the 

 ether or alcohol, a certain amount of power was expended in the 

 improved arrangement. Another method was the chemical one of 

 producing refrigeration by evaporation in connection with ab- 

 sorption. Many vapours ammonia being one of them were 

 readily absorbed by water, but could be separated again by the 

 application of heat to the mixed liquid. A machine on that prin- 

 ciple was shown at the Universal Exhibition, in 1851, by M. Carre, 

 and very good results had been realised by it. It consisted of a 

 boiler which was filled with ammoniacal liquor, and the ammonia 

 vapour was driven off under considerable pressure into a surface 

 condenser composed of tubes surrounded by cool water. A sepa- 

 ration was thus effected by heat of the ammonia from the water ; 

 and the ammonia, after being withdrawn into a vessel of lower 

 pressure, evaporated at a very low temperature, and thus produced 

 refrigeration, the vapours of ammonia being'eagerly absorbed by 

 water of ordinary temperature forming mother liquid for re-evapo- 



