186 FIUF. [Lesson xxvm. 



or density becomes less, then the temperature is 

 increased. Thus when the solution of a mixture 

 of salt and snow is completed, the temperature 

 rises. The whole of these phaenomena, as Dr. 

 Thomson observes, as well as the evolution of 

 heat during putrefaction or fermentation, are 

 readily explained by Dr. Black's theory of latent 

 heat. 



Setting aside certain particularities of a very 

 few bodies, it may be assumed, that every addition 

 of caloric to a body is succeeded by the expansion 

 of that body : and every abstraction of caloric by 

 a diminution of bulk. Gaseous bodies in general 

 expand most : common air expands eight times 

 more than water, and liquids expand more than 

 solids : thus the expansion of water is about forty- 

 five times greater than that of iron. 



Mr. Dalton, of Manchester, has ascertained, by 

 a simple apparatus ; consisting of a graduated glass 

 tube, open at one end, at which end mercury is in- 

 troduced to a given point, the rest of the tube 

 being filled by gaseous matter, the dilation of 

 which is measur-ed by the quantity of mercury, 

 which is forced out by the application of heat to 

 the gas j that all gaseous bodies suffer the same 

 degree of expansion from the same addition of 

 caloric, under the same circumstances : and the 

 increase of bulk it J- part, for 1 elevation of the 

 mercury in the thermometer. M.GayLausac also 

 made a series of experiments, the result of which 

 coincided with that of Mr. Dal ton's. From these 



experiments 



