5-2 



THERMOMETER AND PYROMETER. 



ments have shown that the same quan- 

 tity of caloric which can raise the tem- 

 perature of water only 4, will raise that 

 of mercury 112. If this be the case at 

 every temperature, which is most pro- 

 bable, the quantity of caloric in water is 

 to that in an equal weight of mercury, at 

 the same temperature, as 1 1 2 : 4 =28:1. 

 Besides this method of finding out 

 the comparative quantity of caloric in 

 bodies, there is another founded on the 

 fact, that ice in melting absorbs an uni- 

 form quantity of caloric. Professor 



a, is the innermost ; and is destined to 

 receive the heated body, the subject of 

 experiment. The space between it and 

 the second vessel, b, is to be filled with 

 pounded ice, or snow, as well as the 

 perforated cover, /, of the cage a. It 

 is the melting of this snow which af- 

 fords the indication of the comparative 

 quantity of caloric in the bodies sub- 

 mitted to experiment ; it rests on a wire 

 sieve, at the bottom of the cylinder b, and 

 is received at the orifice of the pipe d. 

 To guard against the effects of external 

 temperature, the cavity between the 

 vessel b, and the exterior one, is filled 

 also with pounded ice or snow ; the ge- 

 nerallid h, of the whole being also covered 

 with snow, and its edges resting in a 



Wilcke, of Copenhagen, first conceived 

 the idea of employ ing the melting of ice or 

 snow, for the purpose of ascertaining the 

 comparative quantity of caloric in dif- 

 ferent bodies ; and this method was im- 

 proved in the hands of Lavoisier and La- 

 place, by the invention of the Calori- 

 meter. 



It consists of two vessels of tinned 

 iron, and a wire cage, which are fitted 

 so that one may be inserted within the 

 other, leaving a cavity between the sides 

 of each. (See Jig. 51.) The wire- cage, 



groove e, lined with the same material, 

 the interior of the instrument is defended 

 from all direct access of external tem- 

 perature. The two tubes, g, in the lid, 

 are for the introduction of thermome- 

 ters; but during experiments those 

 tubes are shut up, to prevent the ac- 

 cess of currents of air through the ca- 

 lorimeter. The water collected between 

 the outer and second vessel may be 

 drawn off by the pipe i. Experiments 

 of this kind should be made in a room 

 at a temperature of 32. Before com- 

 mencing the experiment, the snow is sa- 

 turated -with moisture by its melting, to 

 obviate as much as possible the error from 

 not collecting the whole of the water. 

 The indications of this instrument, 



