Chap. 4.3 Caufe of Fluidity. nj 



which they are produced kept floating in a quantity 

 of fire. To understand how caloric may exift in this 

 combined ftate, without exhibiting any of its deftructive 

 properties, let it be remembered, that fire, like every 

 other body, can be only active while in a difengaged 

 flate. Fire cannot excite in our organs the fenfation 

 of heat, unlefs it penetrates thofe organs ; if therefore 

 it is retained by another body by the force of a fupe- 

 rior attraction, it is evident it cannot affect our organs 

 as it would if in a (late to be attracted by them. In. 

 the fame manner the mineral acids (aquafortis for in- 

 ftance) in a difengaged ftate act with violence on al~ 

 moft every fubftance, and corrode or ulcerate our-flefh, 

 when brought in contact with them ; but if united 

 with a body which poflefles a ftronger attraction for 

 them (fuch as an alkali) they will not leave that body 

 to act upon any other, but are perfectly difarmed of 

 all their noxious qualities : thus the fafe and innocent 

 compound falt-petre is formed from two violently 

 active and corrofive fubftances, a cauftic alkali, and 

 the nitrous acid, or aqua-fortisj and common fait 

 from the fame alkali, and the muriatic acid. 



Every body in palling from a folid to a fluid ftate, 

 or from that of a common to a rarer or elaftic fluid, 

 abforbs a quantity of caloric or fire, and confequently 

 a degree of cold is always produced by the procefs ; 

 and on the contrary, every body in pafiing from a 

 fluid to a folid ftate, or from that of a rarer to that of 

 a denfer fluid, emits a quantity of that fire which kept 

 it in a ftate of fluidity ; and by this procefs, on the 

 other hand, . proportionable degree of fcnfible heat is 

 produced. 



A number of phenomena, which were before un- 

 explained, are now clearly illuftrated by this theory. 

 What is calLed the freezing mixture, it is well known 

 J 3 cbrififts 



