Preservation of Animal Food. 49 



under ground, in well-rammed earth, and furnished with a 

 condensing-pump (worked above ground), and one eduction- 

 pipe, opening by a stop-cock through a hose into water, 

 would in all probability supply an ad libitum quantity of 

 ice for the use of a family in the country, the condensation 

 being performed over night." 



Professor Piazzi Smith, Astronomer Royal for Scotland, 

 proposed to reduce the temperature of rooms in India, by 

 permitting cooled compressed air to escape from a safety- 

 valve into the apartment to be cooled. But this method of 

 employing compressed air is both inefficient and ancient, for 

 the Marquis of Worcester, in the quaint language of the 

 time in which he lived, alludes in his " Century of Inven- 

 tions," to an " artificial fountain to be turned like an hour- 

 glass by a child, in the twinkling of an eye, it holding a 

 great quantity of water, and of force sufficient to make 

 snow, ice, and thunder, with a chirping and singing of birds, 

 and showing of several shapes and effects usual to fountains 

 of pleasure." It is evident that compressed air was 

 employed by the Marquis to produce the snow, ice, and 

 thunder in this remarkable fountain. 



The apparatus I propose to employ to obtain, as nearly as 

 possible, all the cold resulting from the expansion of air with 

 the least possible expenditure of force, consists of an ordinary 

 double-acting force pump, a cooler formed of a number of 

 copper pipes immersed in water, through which the heated 

 compressed air passes, and is deprived of the heat resulting 

 from compression, a receiver for the purpose of accumulating 

 a quantity of compressed air, and a cylinder in which the air is 

 permitted to expand. This cylinder is similar in form to 

 those used in steam-engines, and the lap of the slide valve, 

 together with a link motion, enables the supply of com- 

 pressed air to be cut off at any part of the stroke. The pump 

 and expansion cylinder are bolted down to the same bed- 

 plate in a horizontal position, so that the position of the 

 cylinder is in a direct line with that of the pump ; by this 

 arrangement the force of the expanding air is employed to 

 assist in the condensation of fresh air. The action of the 

 machine is this : air is compressed by the pump, forced 

 through the copper pipes, and deprived of the heat it pos- 

 sesses in excess of the water in which the pipes are placed, 

 conveyed to the receiver, thence to the expansion cylinder, 

 where it is cut off at a certain part of the stroke. This part 

 of the stroke, at which the supply of air is cut off, determines 



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