in Fluids. 373 



of living vegetables are exposed, immersed in water, to 

 the sun's rays ? 



Mr. Senebier has shown that the colouring matter of 

 healthy green leaves of vegetables, which is extracted 

 from them by spirits of wine, and which tinges the 

 spirits of a beautiful green colour, is destroyed, or rather 

 changed to a dirty brown colour, in a few minutes, on 

 exposing this tincture in a transparent phial, and in con- 

 tact with pure air, to the direct rays of a bright sun ; 

 but why should we not consider this process as a real 

 combustion ? 



The Heat acquired by the liquid, which, as I have 

 often perceived in repeating the experiment, is very con- 

 siderable, and the necessity there is for the presence 

 of pure air, that the experiment may succeed, seem to 

 indicate that something very like combustion must take 

 place in it. 



If liquids are non-conductors of Heat, they ought, 

 certainly, on that account, to be peculiarly well calculated 

 for confining and consequently furthering the operations 

 of that Heat which is generated by light, or by any 

 other means, in their integrant particles, or in the infi- 

 nitely small and insulated particles of other bodies that 

 are dispersed about, or held in solution in them ; as I 

 have already more than once had occasion to observe. 



If this supposition be admitted, a very great diffi- 

 culty will be removed in accounting for chemical solu- 

 tion on the hypothesis that the change of form from a 

 solid to a fluid state is in all cases a real fusion ; or that 

 it is effected by the sole agency of Heat; and that con- 

 cretion, or crystallization, is a process in all respects per- 

 fectly analogous to freezing. 



There are but three forms under which sensible bodies 



