XLVIII. NORMAN SELFE. 
a given volume very much greater than ammonia, their relative 
volumes at zero for equal weights being about 1 : 32-4, and thus 
the relative dimensions of the compressors for equal refrigerating 
effects are as = = 7-2 nearly for ammonia, to 1 for 
carbonic acid. This would be an advantage, other things being 
equal, but carbonic acid reaches a critical condition (at 88 Fahr.) 
where its efficiency rapidly falls off when the condensing water is 
warm, and many carbonic acid machines have their refrigerator 
and condenser one inside the other. By this device power is 
expended to cool the condensing water and make the machine 
work, this being totally unnecessary with ammonia, as machines 
using it often work with the condensing water at 90° or over 
without any great falling off in efficiency. Ina paper read before 
the Ipswich (England) meeting of the British Association, om 
“Carbonic Anhydride Machines,” by Mr. Hesketh, one of the 
Directors of Messrs. Hall of Dartford, a firm that has introduced 
these machines all over the world, it is clearly shown that, with a 
machine producing 9,360 tbs. of ice per twenty-four hours, the 
horse power with different temperatures of cooling water varied 
as under :— 
Inlet cooling water Ice in L.H.P. of 
in degrees Fahr. 24 hours. Engine. 
52 9360 tbs. 15°62 
75 . 20°03 
85 - cio te, 
90 re 28-20 
100 42-10 
making it obvious that, in a carbonic anhydride machine, with an 
increase of temperature from 50° to 90° in the condensing waters 
the power required is double, and with water at 100° it is nearly 
threefold. 
The relative efficiency of a cubic foot of ammonia gas under 
different temperatures from 65° to 105° would vary as under ; the es 
1 Bngineering, Nov. 1st, 1895. 
