84 ANNUAL OF SCIENTIFIC DISCOVERY. 



It will be obvious to the slightest reflection, that, as the air, in expand- 

 ing, becomes a powerful absorber of heat, and will greedily take it from 

 all surrounding bodies, ice might be x made by simply immersing the 

 cylinder in which the expansion takes place in water. This pro- 

 cess, however, would be too tardy a one for business purposes ; and the 

 operation, therefore, is prodigiously accelerated by various adjuncts. 

 In the first place, in order that the free heat of the condensed ah* may 

 be extinguished, so as to fit it for its highest degree of refrigerativc 

 effect, without any loss of time, a pump, connected also with the beam, 

 but bearing a very diminished proportion in size to the air-pump, is 

 made to inject a jet of cold water at and during every stroke of the 

 machine. And so, a similar pump projects its measure of an uncon- 

 gealable liquid among the expanding air in the other air-pump, so as 

 to furnish it instantly with the caloric of volume, while the liquid 

 itself becomes cooled at the same time from the heat it parts with. 

 This liquid (a strong solution of salts) is withdrawn from a tank or 

 vessel designed for the accumulation of " cold," into which, after per- 

 forming its duty in the expanding engine, it is again sent back through 

 the eduction valves. In this tank the ice is manufactured by simply 

 immersing water, placed in metallic vessels, in the liquid ; or with the 

 mechanical addition of occasionally breaking up the adhesions of the ice 

 to the sides and bottom of the vessels, so as to present a new surface of 

 water to the action of the external cold. The reservoir of cold, the 

 expanding engine, the injection pump, and, indeed, every part of the 

 apparatus employed in generating or preserving cold, are so thoroughly 

 concealed from sight, and the radiating influence of the external air, 

 by insulating chambers, that the processes going on within them are 

 wholly unperceived. 



It ought to be mentioned that the condensed air, instead of being 

 transferred directly to the expanding pump, as the above description 

 would imply, passes intermediately into a wrought-iron reservoir, large 

 enough to store a considerable number of cylinder-fulls of air, and thus 

 any disadvantage from leakage, or the unequal working of the pumps, 

 is obviated. 



With a machine, having pumps of about eight inches in diameter, 

 and of 1G inches stroke, condensing and expanding air to and from a 

 tension of three atmospheres, a block of ice, weighing nearly 60 pounds, 

 was produced, by the labor of two men, in two hours. 



NEW AGRICULTURAL MACHINES. 



THE Patent Office Report, for 1850-51, contains descriptions of vari- 

 ous new agricultural machines for which patents have been recently 

 granted. The following are especially worthy of notice : A corn- 

 stalk harvester, the frame of which resembles a low three-wheeled truck, 

 and bearing upon its upper surface, near its middle part, two broad 

 metallic disks, armed with teeth on their peripheries, which teeth 

 slightly overlap each other, and are capable of seizing and holding 

 within their grasp any herbaceous matter, and, as the machine moves 

 forward, to tear it up by the roots. The meeting of these teeth is near 



