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140 



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AND 



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body of a determinated bulk, rufh into unioa with and dc- 

 llroy the texture of one another. 



In folutions or cooling combinations no change is pro- 

 duced in the qualities of the bodies. Thus by a folution of 

 nitre in water cold is produced, and the fait may be depo- 

 fited from the water, or the water be evaporated, and 

 neither of the bodies undergo the leaft change. In this 

 cafe it appears, that there is no diffolutionof the conftituent 

 parts of either body, by the attractive force of the other, 

 or by the conftru£tion of their parts; but that the globules 

 of one body adhere fuperficially to thofeof the other, and 

 the particles of the fluid are fimply charged with thofe of 

 the folid, by which means the vibratory motion of the 

 particles isdiminiflaed, whence cold is neceffarily produced. 



It has been obferved that fpirit of nitre mixed with water 

 produces heat, while the fame fpirit mixed with fnow pro-* 

 duces the moft intenfe cold. This may be probably urg- 

 ed as an objedion to the above theory of heating and cool- 

 ing combinations, under the apprehenfion that fnow being 

 nothing elfethan frozen water, fhould on thcfe principles 

 produce the fame effeds, on combination with any third 

 body. But it muft be obferved, that one is a mixture, the 

 other a folution. Water joined with fpirit of nitre produces 

 a mixture, the bodies undergo a change of qualities, and 

 heat is generated. Pour the fpirits of nitre into fnow and 

 nothing will follow, at leaft nothing has followed but a 

 folution of the fnow in the fpirit. For thefe experiments 

 have always been made when the temperature of the 



fpirits was much below the freezing point of water, fo that 

 the fnow could not be melted by fuch combination. Hence 

 there being no intimate union of the parts, nor any thing 

 elfe than a proper folution, cold was generated as in all 



fimil 



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fcs. 



3. Heat produced by fermentation or putrefadion, may 

 be accounted for in the fame manner as that produced by 

 chymical mixture, there being no doubt that new mixtures 

 are conftantly forming in every putrefcent or fermenting 

 body. A, Heat 



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