

.s/A' WILLIAM SIEMENS, F.R.S. 2OI 



the cylinder into chambers a, a, forming the inner sides of the 

 cistern, which chambers are perforated towards the bottom to 

 allow the air to bubble through the solution. The cistern to be 

 about 10 feet long, by 5 feet broad, by 2 feet 6 inches deep. The 

 t \|i;itided air issues from the cistern into the atmosphere through 

 a series of vertical tubes contained in a cylindrical air-tight 

 chamber (C) through which the compressed air circulates on its 

 way to the cylinder. The compressed air enters the annular 

 chamber through a pipe &, and issues into the tube chamber (('), 

 through a number of holes in order to distribute it uniformly. It 

 then descends gradually, and effects an interchange of temperature 

 with the expanded air within the tubes, which latter issues at the 

 top at nearly the temperature of the compressed air on entering, 

 whereas the compressed air reaches the expanding cylinder nearly 

 at the temperature of the cold cistern, or below the freezing point. 

 The annular chamber d, serves to collect the cold compressed air 

 at the bottom, and to supply it to the admission valves e and /, 

 by means of pipes not shown. The tube in the centre of the 

 chamber C is of about 9 inches diameter, and contains a cylindrical 

 vessel, g, filled with water, which enters the same from above, and 

 is withdrawn at the bottom in a cooled condition to fill the former 

 for the production of ice. The tube surface required is about 

 200 superficial feet. 



"The advantages obtained by this exchange of temperatures 

 are very important. The compressed air is reduced below freezing 

 point before it reaches the expanding cylinder, and the aqueous 

 vapour it contained is at the same time condensed upon the tubes. 

 Indeed the lower the temperature of the cistern descends, the 

 more will the compressed air be reduced in temperature, and the 

 cold produced will accumulate in intensity to any desired degree. 

 Both injection pumps and one of the large air receivers will be 

 dispensed with, for it makes no difference at what temperature 

 the compressed air enters the exchanging apparatus. I should 

 recommend, however, to retain the injection pump of the com- 

 pressing cylinder till the efficacy of the new apparatus has been 

 proved by experiment. 



"This new apparatus would reduce the different losses of 

 refrigerating effect in the following proportions, according to my 

 estimation, viz. : 



