78 ANNUAL OF SCIENTIFIC DISCOVERY. 



ments, in the course of which several aerometers were torn to 

 pieces by the force of the current of air created." 



THE MODERN ICE MACHINE. 



The amount of ice produced by an ice macliine, worlvcd by 

 means of an exhaust or condensing air-pumj), driven by steam- 

 power, is easily determined, theoretically, from the amount of 

 coal burned in the furnace of the steam boiler. It has been 

 proved that the combustion of one pound of antiu'acite coal pro- 

 duces, in round numbers, 14,000 units of heat, and that in order 

 to freeze water of 72° F., it is necessary to abstract, besides 40° 

 of sensible heat, 140° of latent heat — together 180° — which, for 

 one pound of water, is, of course, equivalent to 180 units of heat. 

 As this number of units is the eightietli i)art of the 14,000 units 

 produced by the combustion of one pound of coal, it is clear that 

 the heat produced by the combustion of one ton of coal is equiva- 

 lent to the heat to be abstracted from 80 tons of water of 72°, in 

 order to change it to ice. 



But in practice we find here exactly the same state of aflairs as 

 is the case with the steam engine. Theoretically, a steam engine 

 ought to produce at least 700 units of force (foot-pounds) for 

 every unit of heat consumed ; in practice, good machinery only 

 produces from about 70 to 100 foot-pounds, from about one-tenth 

 to one-seventh part of the theoretical amount. In the best ice 

 machines, thus far constructed, instead of freezing 80 tons of 

 water for ever}' ton of coal consumed, only from about 8 to 11 

 tons of ice are produced, also from one-tenth to one-seventh part 

 of the theoretical amount ; proving, thus, the remarkable f;xct, that 

 in both the steam engine and the ice machine exactly the same 

 relation exists between the theoretically calculated effects and the 

 practical results. 



As, however, all the best ice machines accomplish the conver- 

 sion of the heat of thcv^uel into the freezing operation by the in- 

 tervention of a steam engine, the fact that they practically pro- 

 duce only from one-tenth to one-seventh of the amount of the 

 cold they theoretically should produce, is solely due to the other 

 fact, that the steam engine, itself, practically produces only from 

 one-tenth to one-seventh of the amount of power which would be 

 strictly equivalent to the number of heat units consumed. It must 

 not be lost sight of that it is only the power of the steam engine 

 which generates the cold in the freezing machines, and that, 

 therefore, improvements in the steam engine, wliicli bring its 

 practical results nearer to the theoretical standard, will at once 

 exert their influence on the amount of ice the ice machines can 

 produce, and, consequently^ also on the cost of the ice manufac- 

 tured in these machines. • 



Moreover, it appears that the kind of freezing machines in 

 question, which convert power into cold, notwithstanding they 

 are yet in their infancy, have already attained such a degree of 

 excellence, that they are ahead of that class of m;jphine5 which 



