COLD. 



733 



Cold. described, and then exhausting the air. He therefore 

 '""Y"*"' attempted to freeze mercury, by incrusting the bulb of 

 a thermometer with a thin coating of ice, and then expo- 

 sing it in (hat state over a cup of sulphuric acid, under 

 an exhausted receiver; but the experiment was unsuccess- 

 ful ; for, though the reduction of . temperature was con- 

 siderable, the mercury, owing to the imperfection of the 

 air-pump, was not frozen. Soon after, however, he had 

 an opportunity of trying the experiment a second time, 

 with the very excellent air-pump constructed by Miller 

 and Adie already mentioned, when he had the high gra- 

 tification of realizing his conjecture, and seeing the mer- 

 cury in the bulb of the thermometer partially congeal. 

 For the sake of those who may wish to attempt this very 

 beautiful experiment, we may mention, that the air-pump 

 should be sufficiently powerful to bring the gage within 

 -,'j-th of an inch at least of the barometrical column, at the 

 time of the experiment ; and that the sulphuric acid em- 

 ployed for absorbing the vapour of the ice, should be in 

 the most concentrated state in which it can be procured. 

 The crust of ice which enveloped the bulb of .the ther- 

 mometer in this experiment of Mr Leslie, was attached 

 to it, by suspending the instrument from a rod, which 

 passed through a collar of leather on the top of a recei- 

 ver, and then alternately immersing the bulb in .a cup of 

 water, and exposing it, in circumstances already mention- 

 ed, to the cooling influence of evaporation in a partial 

 vacuum. The cup of water was placed immediately un- 

 der the bulb for the conveniency of the immersions, and 

 removed from the receiver when the crust of. ice on the 

 bulb was sufficiently thick. The bulb with its coat of 

 ice was then suspended about ;in inch above the cup con- 

 taining the sulphuric acid, and the receiver was exhaust- 

 ed, until the gage was brought to within -i^th of an inch 

 of the height of the barometrical column, at the time of 

 the experiment. After the experiment had been allow- 

 ed to proceed during half an hour, a sudden contraction 

 was observed in the mercury ; the air was re-admitted, 

 and the thermometer being withdrawn as quickly as pos- 

 sible, it was found, on breaking the bulb, that a small 

 portion of the mercury was actually in a solid state. 



We have performed this experiment with the same air 

 pump, by arranging the apparatus a little differently, and 

 with a more decisive icsult, as the congelation of the 

 mercury was more rapid and complete. The principal 

 difficulty in Mr Leslie's mode of performing the experi- 

 ment, is experienced in giving the coating of ice to the 

 thermometrical bulb. We avoided this, by taking a lump 

 of solid ice, and giving it, by means of a piece of hot 

 iron, the shape ofa cup about ^th of an inch thick. This 

 cup was suspended in net-work, about an inch above the 

 sulphuric acid. The mercury to be frozen, which was 

 previously reduced to 32, to prevent it from melting 

 the bottom of the cup, was poured into it, and then co- 

 vered with a shallow stratum of water, about the same 

 depth as the thickness of the cup. The whole was co- 

 vered with a receiver, and the air was exhausted as quick- 

 ly as possible. The water above the mercury was imme- 

 diately frozen, so that the mercury was completely enve- 

 loped in ice, and in contact with it. The air of the room 

 wa about 60, and the gage was brought within T 'j-th 

 of an inch of the height of the barometrical column. In 

 about 3 minutes, the ice began to exhibit an evident ap- 

 pearance of a rapid waste by evaporation, its surface be- 

 coming rugged and uneven. It then cracked in several 

 places and discovered part of the mercury, which seemed 

 to be in the solid state. At the end of 6 minutes, the air 

 was re-admitted, and the cup of ice being taken out of 

 the receiver and broken, the mercury was found to be 



completely solid. It sustained repeated blows pf a ham- 

 mer, and appeared to possess an imperfect degree of mal- 

 leability. A part of it being thrown into water, was im- 

 mediately surrounded with a shell of ice. 



The third method of producing cold which we propo- 

 sed to consider, is liquefaction induced by chemical ac- 

 tion. We have already explained (see CHEMISTRY, page 

 42) the general principles upon which the reduction of 

 temperature by liquefaction depends. We shall now give 

 a more detailed and practical view of the subject. 



The solution of salts in water, by the transition to the 

 fluid state, is always accompanied with a considerable 

 diminution of temperature. When nitre is added to wa- 

 ter, at the ordinary temperature of the atmosphere, until 

 the water is saturated, the temperature is reduced 15 or 

 16 degrees ; and a still greater degree of cold is obtained 

 by the solution of muriate of ammonia. But of all the 

 salts, nitrate of ammonia seems to undergo the greatest 

 reduction of temperature during its solution. If it be 

 mixed, in the state ofa fine powder, with an equal weight 

 of water, the temperature is reduced from 50 to 4. 



The greatest number of experiments on this subject, 

 have been made by Mr Walker of Oxford. Being 

 aware that water, saturated with one salt, was still capable 

 of dissolving a portion of another, he inferred, that a 

 greater reduction of temperature would be obtained, by 

 dissolving different salts in succession, than by the solu- 

 tion of any one of them separately. The conjecture was 

 confirmed by experiment. We have already mentioned, 

 that nitrate of ammonia being dissolved in an equal 

 weight of water, reduces the temperature of the ingredi- 

 ents from 50 to 4 ; but if an equal weight of carbonate 

 of soda be added, the temperature is reduced from 50 

 to 7, though the latter salt, when employed alone with 

 water, has but little frigorific effect. 



As the production of cold, by freezing mixtures, de- 

 pends partly upon the rapidity with which the substan- 

 ces employed pass into the liquid state, and partly upon 

 the increase of capacity fsrr caloric which is acquired by 

 that transition, it might be expected that a greater re- 

 duction of temperature would be obtained, by dissol- 

 ving salts in acids than in water. Accordingly, by dis- 

 solving a pound and a half avoirdupois of Glauber's salts 

 (sulphate of soda) in 12 ounces of nitrous acid, previous- 

 ly diluted with 6 ounces of water, Mr Walker obtained a 

 diminution of temperature from 50 to 1 ; when sul- 

 phuric acid, diluted in the same proportion, was employ- 

 ed, the reduction was from 50 to 5 ; and three parts 

 of the same salt by weight reduced to afine.powder, and 

 dissolved in two parts of muriatic acid, sunk the ther- 

 mometer from 5O to zero. The reduction. of tempera- 

 ture is still greater, when different salts are employed at 

 the same time. Thus, nitrate of ammonia 6 parts, phos- 

 phate of soda 9 parts, and diluted nitrous acid 4 parts, 

 all by weight, reduce the temperature of the mixture 

 from 50 to 21. This is a diminution of 71, and is 

 the greatest degree of cold that can be procured by a 

 single mixture yet known. Mr Walker succeeded in 

 freezing mercury, by cooling, in a succession of these 

 mixtures, the ingredients by whose liquefaction the con- 

 gelation was ultimately to be produced, though the tem- 

 perature of the air at the commencement of the experi- 

 ment was 4.5. Thus, let the mixtures be represented by 

 A, B, C, D : the ingredients for the mixture B were 

 cooled by A ; those for C by B ; and lastly, tho.se for 

 D by C i so that the ingredients for the last mixture* 

 were at a very reduced temperature, before they were 

 exposed to mutual action with one another. 



When ice or snow is dissolved in acids, .the solatioa 



Cold. 



Production 

 of cold by 

 liquefac- 

 tion. 



Solution of 

 salts in wa- 

 ter. 



Solution of 

 salts iu a. 



cids. 



