488 FREEZING 



able to somo important usos. Water in freezing really rejects everything it may 

 contain even air, and hence solid ice is actually pure water. This may bo easily 

 proved. Make a good freezing mixture, and place somo water in a ilask, and while 

 it is undergoing consolidation by being placed in the frigorific compound, gently agi- 

 tate it with a feather. Now, if the water contains spirit, acid, salt, or colouring 

 matter, either of them are alike rejected, and the solid obtained, when washed from the 

 matter adhering to its surface, is absolutely pure solid water. 



This philosophic fact, although it has only been subjected to examination within 

 the last few years, has long been known. 



Byron, in his 13th canto of ' Don Juan,' has the following allusion to it : 



" I'll have another figure in a trice : 



What say you to a bottle of champagne ? 

 Frozen into a very vinous ice, 



Which leaves few drops of that immortal rain, 

 Yet in the very centre, past all price, 



About a liquid glassful will remain ; 

 And this is stronger than the strongest grape 

 Could e'er express in its expanded shape." 



The old nobles of Eussia, when they desired a more intoxicating drink than usual, 

 placed their wines or spirit in the ice of their frozen rivers, until all the aqueous 

 portion was frozen ; when they drank the ardent fluid accumulated in the centre. 

 This plan has been employed also for concentrating lemon-juice and the like. 



The manufacture of ice by machinery is one of the many interesting applications 

 of science, and this has now become a practical trade. In 1851 M. Eezet, of Rouen, 

 volatilized ether in a close vessel by exhausting the air from its surface. After the 

 air, the ether-vapour itself was exhausted by a pump, then condensed by the aid of 

 cold water, and forced back into the same vessel, by which a continual absorption of 

 caloric from the surrounding bodies was effected, and a continual refrigeration obtained 

 as long as the circulation of ether was kept up by working the pump. 



Harrison's ice-making machine, and its improved form by Mr. Siebe, is a particular 

 application of the exhausting air-pump. The working of the process is as follows : 

 A quantity of sulphuric ether, contained in a close vessel surrounded by a current of 

 salt water, is made to pass rapidly into a state of vapour by the action of a large air- 

 pump driven by steam-power ; the necessary amount of heat requisite to effect this 

 change in the ether is abstracted from the surrounding salt water casing, which is thus 

 cooled to a temperature below the freezing point of water, and is then made to circu- 

 late through a box, containing the water to be frozen, in tin moulds arranged on a 

 travelling frame, which moves in a direction contrary to the refrigerating current. 

 The ether-vapour removed at every stroke of the pump is passed over to a condenser, 

 where it reassumes the liquid form, and is returned to the evaporating vessel. 



It will bo seen that the principle in the machines of Harrison, Rezet, and Siebo is 

 the same. The machine invented by M. Carre appears to be much more effective. 



Messrs. Carre and Co.'s ice-making machines are of two kinds, one being con- 

 tinuous, and the other intermittent in action ; but the principle involved is the same 

 in both cases, viz., the production of cold by the volatilisation of a gas which is easily 

 liquefiable, and at the same time in a high degree soluble in water. The smaller, 

 or intermittent apparatus consists essentially of a pair of distilling and condensing 

 vessels, united together by an air-tight joint, and capable of resisting an internal 

 pressure of 150 Ibs. to the square inch. The distilling vessel is filled with a watery 

 solution of ammonia, at the maximum point of saturation. By the application of 

 heat, the ammoniacal gas is driven off, and passes over into the receiver or con- 

 densing vessel, where it is soon liquefied by the constantly increasing pressure of the 

 gas given off by the watery solution, a pressure of 97 Ibs. to the square inch being 

 sufficient to effect the liquefaction of the gas, when the temperature of the vapour 

 does not exceed 50 Fahr. When the condenser is filled with pure fluid ammonia, 

 the distilling vessel is removed from the fire, and is immersed in a vessel of water 

 at the ordinary temperature of the air. By this means the water remaining in the 

 distilling vessel is slightly cooled, and it immediately redissolvos the column of 

 ammoniacal gas standing above it, a vacuum is formed, and the liquefied gas imme- 

 diately begins to distil back and redissolve. The heat necessary to effect this 

 redistillation is abstracted from the water to bo frozen, which is contained in a 

 cylindrical mould, placed in the internal tube of the annular condensing vessel. The 

 time required for producing 1 Ib. of ice in the smallest size of the portable apparatus 

 is 55 minutes ; 25 minutes being required for the preliminary, and 30 minutes for the 

 reverse distillation ; it is during the latter period that the ice is produced. About four 

 pounds of ice are produced for every pound of fuel consumed in tho preliminary 

 distillation, 



