1 62 Whether Chemical Affinity he nti the mere EffeSi of Temperature ^ 



in the third chapter of the preftnt EITay, he has 'extended the application of his dif« 

 <-ov€ries to the means which appear to have been ufed fey the Creator of the world, to 

 render the temperatures of different climates more nearly equal by means of the fait water, 

 which covers fo large a part of the furface of the globe. But the mofV interefting applica- 

 tion remains to be made of this doftrinp to chemiftry, vegetation, and the animal economy \ 

 to the learned in which branches of fcicnce he begs leave moft earneftly to recommend 

 them. From his meditations he thinks it not improbable that every change of ftate, in 

 every kind of fubftance, may be owing to heat a|lone ; that every concretion is a true con- 

 gelation efteiTted by cold, or the diminution of heat; that every change from a fqlid 

 to a fluid form is a real fufion ; — and that it may be found, that the apparent violence witli 

 which certain foiids are attacked by their folvents, is not owing to any particular or elcdlive 

 ^ttradion, but to the confiderable degree of heat or cold, find the great difFerence of fpe- 

 cific gravity which enfues in the folvent, from this caufc as well as from the fubfequent 

 change produced by combination. 



If fluids be non-conduflors of heat, it will neceflarily follow, that change of temperaturja 

 \vill produce currents in every chemical folvent, in proportion to the change of fpecific 

 gravity ; and the rapidity of the procefs of folution will be proportioned to that of the cur-* 

 rents, or to the change of temperature. And again, if the faturated folution be either 

 Javier or lighter than the folvent itfelf, currents will be produced from this caufe alfo^ 

 which wi!l tend to render the folution more or lefs rapid, according to the magnitude of 

 this difference, and its direftion with regard to the otner difference caufed by the change of 

 temperature. An inftance of thefe two caufcs operating jointly is adduced in the folution of 

 fommon fait in water. If this folid be fupported in a perforated veffd under water, but 

 near its furface, the folution will be moft rapid : flrfl:, becaufe the temperature is dimi- 

 nifhed, and confequently the water is condenfed in the procefs ; and, fecondly, becaufe the 

 folution of fait in water is itfelf more denfe than the water itfelf. On both accounts there- 

 fore the brinp will rapidly defcend, and frefli portions of the folvent will continually be 

 brought in contaiSl with the fait. 



On this occafion the author propofes a curious queftion : Whether, in a cafe where the 

 expanfion by heat were equal to the condenfation by the procefs of chemical union, the effe£l 

 ^f folution could take place? — He anfwers by obferving, that if chemical attraflion, as has 

 been generally fuppofed, really exifts and operates in the way of prediledlion beyond the 

 point of a6lual contaft, it is probable that the folution would take place. — But if this at- 

 jra£lion be nothing mere than has been juft pointed out, it would loUow that though fclution 

 would not be abfolutely impoffible, yet it would be fo flow as hardly to be perceptible. 



In the confideration of the foliition of fait in water, the pofition of the folid near the 

 furface of the fluid, was ftated as a circumftance effential to its rapidity. The uniform 

 diffufion of foiids tliroush the whole mafs of lighter fluids which diffolve them, has ufually 

 been confidered by chemifts as a proof of attraction between the two bodies operating at a 

 ^iftance from the place of contaft. It fccms to be a flriking refult ef the Count's reafon^ 

 ing, that if no otlier caufes fhould interfere but thoie which flow from the mutual combina- 

 tion of the two fubftances, the fait would not, at lealt in any moderate portion ot time, be 

 carried to the upper part of the fluid relling upon it. He made this the fubjedt of a par- 

 ticular experiment. 



A cyjin- 



