ICE-HOUSES. 



511 



part being uppermost, would approach 

 the form of a sphere as the reduction of 

 its length, from the above-mentioned 

 causes, was being effected; and by the 

 time that the heat of the summer be- 

 comes most trying, the ice would be in a 

 form more nearly spherical than if it had 

 been perfectly so when first stored in. 

 Another advantage may be mentioned 

 as belonging to a circular building — and 

 that is its strength, compared with one 

 of which the walls are straight, and liable 

 to be forced in by the external pressure 

 of the surrounding soil." — Gard. Chron* 

 1841. 



The fact of ice-houses built upon the 

 very same plan as to form, and of the 

 same size, and filled in the same manner, 

 keeping ice for two years and upwards, 

 while others do not preserve it nine 

 months, is sufficiently well known. We 

 must therefore look to something more 

 than form and size to account for this 

 difference. And first, let us observe, that 

 heat and moisture are the two principal 

 causes of dissolution, and that air, appa- 

 rently the principal thing hitherto 

 guarded against, has not the same effect. 

 Indeed it has been suggested to ventilate 

 the ice-house at top, occasionally, to let 

 off the accumulated vapour supposed by 

 some to accumulate over the surface of 

 the ice in the house ; while others have 

 recommended leaving the doors frequent- 

 ly open during the night, for a somewhat 

 similar reason. If air, says a third party, 

 can be admitted under and around the 

 body of ice at a low temperature, and 

 that body of air kept in a quiescent state, 

 it will be the best medium to secure its 

 preservation. That the ice should be 

 completely separated from the earth, by 

 walls of great thickness, or, still better, 

 by hollow built ones, is quite clear, were it 

 for no other purpose than to prevent the 

 conduction of heat ; while, at the same 

 time, this provision would counteract the 

 effect of damp also, so far as its entrance 

 through the roof and sides is concerned. 



In accordance with these views we find 

 a clever article in " The Gardeners' 

 Chronicle," from which we extract as 

 follows : — " The temperature of the earth 

 in Britain, so far as the excavation of an 

 ice-house is concerned, may be stated to 

 average from between 48° and 52° Fahr., 

 and the atmospheric temperature about 



50°. The earth parts with its heat, and 

 communicates the same to bodies in con- 

 tact with it, much quicker than the air. 

 Hence it becomes desirable to prevent the 

 immediate contact of the ice with other 

 substances, by interposing some slower 

 conductors of heat. On observing the 

 comparative effects of water and air, both 

 of the same temperature, in lowering a 

 thermometer as much as 50°, it was found 

 that the depression was accomplished by 

 the water in one-twentieth of the time 

 required by the air. Hence the contact 

 of ice with water should be prevented by 

 proper drainage. Indeed, too much at- 

 tention cannot be paid to this most essen- 

 tial operation. That the rain should be 

 excluded directly from the roof, it is 

 scarcely necessary to mention ; but its 

 approach to the sides by percolation 

 through the earth should also be guarded 

 against, otherwise it will occasionally in- 

 troduce a temperature of more than 60°. 



" As air is a very much slower conduc- 

 tor of heat than either earth or water, it 

 might be concluded that if the ice were 

 surrounded by air at the sides, and 

 partially at the bottom, by resting on a 

 wooden grating, it would be in the most 

 favourable situation for preservation. 

 A cavity is gradually formed at the sides 

 in consequence of the melting of the ice ; 

 and if the air in the cavity as formed 

 were to remain perfectly at rest, it is 

 probable that no substance would occa- 

 sion less thawing — taking into considera- 

 tion the fact, that substances possessing 

 non-conducting properties in a higher 

 degree than air, when they are dry, lose 

 less to a considerable extent when exposed 

 to wet or damp. It must, however, be 

 observed, that in a clear cavity between 

 the ice and wall, a constant though slow 

 circulation of air will take place from the 

 following causes : The portion of air 

 next the ice is affected by a temperature 

 of 32° ; that next the earth or wall is 

 heated by being in contact with substances 

 communicating a temperature of about 

 50° : such portion consequently ascends, 

 whilst that next the ice descends in con- 

 sequence of its greater density ; but as it 

 sinks, a supply from the warmer side must 

 be drawn to occupy its place. It is there- 

 fore evident, that if the continuity of this 

 circulation would be intercepted, the 

 free interchange of particles would be 



