On Capillary ASlhn. 2oi 



aftion. The efteA is produced by the attraftion of the nu- 

 nierous proximate facets ; and it is the more notable, as the 

 agaregaic furface is very large in comparifon with the inter- 

 ftTces'to be filled up with humidity. But the abforptlon of 

 water by bibulous paper, linen, or flannel, though com- 

 monly referred to the fame caufe, is of a very different na- 

 ture. From clofe obfervation I am convinced that in thofe 

 inftances there occurs a real though not a permanent change 

 of conftitution : the folid begins to affimilate itfelf to the 

 qualities of the combined fluid, and becomes fofter and more 

 tranflucid. By means of an inftrumeut, contrived to mea- 

 fure the fmalleft alteration of volume, I have proved deci- 

 fively that the union of water or oil with paper or linen is 

 accompanied with a general contraflion or concentration of 

 the mafs. Nay, applying a delicate thermometer, I perceived 

 a very fenfible extrication of heat invariably to take place 

 durinn; fuch combinations. And this effeft was the greater 

 in proportion to the previous drvnefs of the folid. Thus I 

 have fomclimes produced a heat of ten degrees by moiftening 

 faw-du(t which had been parched before the fire. An ab- 

 forption of this kind is (iriftly a chemical procefs : the in- 

 ternal firufturc of the folid is altered, and a force is deve- 

 loped very diftinft in quality and degree from what obtains 

 in capillary aftion. The contemplation of fuch fafts may 

 ferve to extend our ideas of chemical agency. The ftate of 

 fluiditv IS eflTential to its operation; but that quality is re- 

 quired only in one of the ingredients, and the refult of the 

 combination may be indifl'erently a fluid or a folid. Copper 

 will imbibe quickfilver and become only more brittle; and, 

 on the other hand, quickfilver will diflblve a fmall portion of 

 copper without relinquifliing its fluid charafter. Nay, if the 

 one fpecies of combination can be produced, we may fafely 

 infer the exift:ence of the other. Thus all ftones are found 

 to contain water incorporated in their fubftance, altogether 

 diftin£l from what may infinuatc itfelf in their accidental 

 crevices. If we rcverfe the combination, therefore, and fup- 

 pofc the fluid to predominate, we fliall conclude that water 

 is to a certain detirec capable of diflblvinnf all forts of ftones. 

 And if, difrecarding the authority of difputcd fyltems, we 

 candidly examine the numerous fa6ls that occur in geology, 

 we cannot hcfitate to admit the jullncfs of the propofition. 

 I would not venture, however, to maintain that wafer is 

 finglv capable of diflolving the hardcft floiie; for the cohefion 

 ot the integrant molecules will, in lome cales, oppofe a force 

 lupcrior to the attradlion of the water, i'ut the procefs may 



be 



