m 



ON CHEMICAL ATTEACTION. 



the influence of the attraction of ag^gregation is alleged aa 

 the cause of the decomposition of the quaternary coni pound, 

 and of ilie forinatiou of the two bi.iary coin|jouiids obtained 

 by crystallization ; but in this instance the baine mcol^- 

 fiistency occurs, as has been [)ointed out, in considerinjj; the 

 formation of sulphate of lime on theyarae principle. A power 

 developed at the instant of the formation of a compound. 

 is represented as the cause of the formation of that compound. 



Hence it appears, that, supposing the solution to contain 

 a quaternary compound, no reason can be given, why this 

 compound is not obtained, on the eva[)oration of the sol- 

 vent; the inference therefore niust be, that such a com- 

 pound did not exist in solution ; but that the substances dis- 

 solved are really binary compounds, such as we obtain them, 



And. even on the opposite supposition, that cohesion 

 ^oes not at all depend on heterogeneous affi;nty, 1 think the 

 same inference might be deduced. If a solution contain a 

 quaternary com[)ound, which becomes two bmary cocn- 

 pounds on evaporation; this change must tiske place, at 

 the instant of crystallization: but why 



th( 



it does take place 

 is no new power 



at that instant, we are not told 



called into action ; becautte Berthollet's notion of the force 

 of cohesion is, that it is a power not only when apparently 

 effective, but also when it appears to be entirely overcome. 

 iThe question then remains, if the solution be that of a qua- 

 ternary compound, what is the reason, that, at tjie point,of 

 jCrystallization it is decomposed, and that two binary com- 

 pounds are obtained on evaporation ? 



Speaking of the influence of volatility on 4i,ffinity, B(pr- 

 tholiet remarks, that " heat, by increasing the volatility of 

 *' a substance, enfeebles its combination, and this cause is not 

 *' less efficient in complex, than in elective affinities: it is 9, 

 *• force added to those already in action, gmd which determines 

 " the union and separation o? those substances, which are most 

 " disposed to fprra ■i volatile componnd y Still the same ob- 

 pou'nd cannot j^^tion may be urged against this observation, as was offered 

 to the alleged influence of cohesion in effecting combina- 

 tion. The volatility of a compound can have no influence 

 on the formation of^that compound; combination, in erej-y 

 in^tau^e, depends on the properties of the constituents^ and 



yoliitility. 



That of a re- 



influence its 

 formatioa. 



