DU MOT AY'S PROCESS OF ICE-MAKING. 799 



walls or ceiling of tlie chamber to be cooled. The discharge-pipe of 

 the circulating pump communicates with a condenser, which consists 

 of a tubular vessel immersed in a tank containing cooling water taken 

 from any convenient source and kept in constant circulation. The 

 volatilized liquid is expelled from the pump into this condenser, where 

 the process of condensation or liquefaction of the gas is completed. 

 The restored liquid is then returned to the refrigerator by suitable con- 

 nections, to be again volatilized, and so on continuously, the waste of 

 the agent being but trifling. 



The time consumed in the process of freezing the water-cans 

 ranges from twenty-four to thirty-six hours. The more perfect the 

 insulation of the tanks in which the water-cans are immersed, the 

 more quickly is the latent heat extracted from the water ; and this, 

 after all, is the problem involved in artificial freezing. To speak of 

 the manufacture of cold, though popularly comprehensible and con- 

 venient, is to misapply terms. In one sense heat seems to be but an 

 incident of the cosmic order, an exception to a state of things pervad- 

 ing interstellar space, and toward which the warm earth, and her sister 

 planets, and all the burning orbs of heaven, are gradually tending. In 

 producing cold we therefore seem but to assist Nature to re-establish, 

 in an infinitesimal degree, the state of comparative molecular inac- 

 tivity that distinguishes cold from heat, and which characterizes the 

 vacuum. 



The need of an efficient system of artificial refrigeration is con- 

 stantly increasing. Not alone in warm countries is ice rapidly be- 

 coming a u.niversal necessity, but, in myriad industries in temperate 

 climes, the economy experienced by using air-cooling contrivances in 

 the place of Nature's unwieldy, slippery, and not always obtainable 

 product, has long since been satisfactorily demonstrated by the wide- 

 spread use of various systems of machines. 



In the years to come, thei'e may arise some engineering genius bold 

 enough to conceive and skillful enough to execute a plan for tapping 

 the limitless reservoir of cold that pervades interplanetary space, and 

 bringing a supply, regulable at will, to a sweltering world. This 

 would be a highly satisfactory solution of the problem of such interest 

 to nine tenths of humanity for a large portion of the year, how to 

 keep cool. Pending, however, the realization of such a scheme, of 

 which it must be confessed there is no immediate prospect, it is diffi- 

 cult to discern any way to an improvement, in this branch of physics, 

 on the latest product of French inventive genius. 



