SIR WILLIAM SIEMENS, F.R.S. 199 



be observed tho compressing cylinder did its work remarkably 

 well, whereas the duty obtained from the expanding cylinder falls 

 manifestly short of the results indicated by theory. It was 

 necessary then to inquire carefully into the causes operating 

 a.u'ainst the performance of the expanding or freezing apparatus, 

 and the following are the results of that enquiry : 



" 1. The power developed in the expanding cylinder should be 

 _'.")!' H.P., whereas only 16*5 H.P. was actually indicated (when 

 no solution was injected) owing to 



"a. A great loss of pressure between the cylinder and the 



receiver. 

 " b. Excessive expansion beneath the atmospheric line, which 



involves a loss of power on the return stroke. 

 " c. Imperfect adjustment of the admission valves. 



"2. When solution was injected the indicated power rose to 

 21*15 H.P., or G'93 H.P. higher than before, which excess of 

 power may to a great extent be fictitious, being caused by the 

 penetration of the solution into the indicator, but it proves that 

 considerable force must be expended in forcing and agitating the 

 solution, and all the power so spent will produce its equivalent of 

 heat and must be deducted, besides the power lost in friction of 

 piston, from the indicated 16'5 H.P. in estimating the refrigerating 

 effect to be produced. 



" 3. The compressed air being cooled by injection of cold water, 

 it will certainly be saturated with vapour, which vapour will be 

 condensed and converted into ice during expansion, and produce a 

 white fog pervading the expanded air. 



" The quantity of vapour so condensed and congealed, supposing 

 the temperature of the compressed air in the reservoir to be 68 

 Fahrenheit, amounts to O'OG Ib. per minute, yielding about 1330 

 units of heat, which represents a loss = 1'9 H.P. 



" 4. The expanded air leaves the apparatus at the temperature 

 of the cistern, or say at 20, which is 6 8 -20 = 48 below the 

 temperature at which it entered the compressing cylinder, 

 which represents a loss of effect = 312 units = 7'25 H.P. at 

 least. 



" 5. The cistern containing the solution, the expanding cylinder, 

 the pump and the connecting pipes, present an aggregate surface 



