ON CHEMICAL ATTRACTION. 2Q1 



not on the substance constituted. If the constituent parts 

 of a compound be volatile, this volatility will be increased 

 by heat, and their union will probably be promoted ; but it 

 is of no iuip(9rtance whether the conmpound be volatile tJr 

 fixed when formed. 



Berthollet has explained in a far more satisfactory man- Causes of li- 

 ner than former chemists the causes of some of the limits, "'/combina^*' 

 which are observed in chemical combination ; he has pointed tion according 

 out the influence of quantity, cohesion, volatility. But ^^^^"*^°''^** 

 there still remains considerable difficulty in accounting for 

 these limits on many occasions; {»:S in the following in- 

 stance, where condensation is considered as the cause, deter- 

 mining the proportion of the constituent parts of the com- 

 pound, and aftbrding the limit to combination, 



" When, in the progress of combination, the result in any Great cotjdtn- 

 *' part of it is great condensation; this, by the obstacle it ^*"""" 

 *' may oppose to the exertion of affinity, or even by the 

 *' greatness of the condensation withdrawing the product 

 *♦ from the sphere of action, may limit the combination to 

 *« that point, or to the propovtion at which tpis effect is 

 ^* greatest; or if by particular circumstances this is over-^ 

 •' come, in the fAvther progress of combination it may hap- 

 " pen ; and in this way, compounds in two or three deter- 

 " minate proportions may be formed.*" I am not certain. Combination 

 with what proprietv we speak of the " progress of combina- Probably not 

 . ,, , T i' 1 1 1 progressive m 



tion ; because 1 do aot know, that we have any reason to respact to pie- 

 believe it to be progressive', progressive in the sense im- P°''^*°'"'®- 

 plied, in relation to proportions. If oxigen be combined 

 with hidrogen, the compound is established in a certain de- 

 terminate proportion ; nor have we any reason for suppos- 

 ing, that the combination ever took place in any other pro- 

 portion ; much lefs can we presume, that the proportion of 

 one or the other increases progrtsssively, until the occur- 

 rence of a considerable condensation puts a period to the 

 progress of combination, and determines the proportions of 

 the compound. The cause of the condensation is likewise 

 unknown; unless it be attributed to the formation of new 

 imtegrant particles, possessed of a new attraction ; which ia 



* Murray, vol. 1, p. 105. 



