*]% Refearcbes refpeSling 



7th, Another circumftance which may change the a&ior> 

 of complex affinities is, the formation of a tiiple fait which 

 is precipitated ; but, by knowing the degree of the fallibility 

 of this combination, we may ftill forefee the composition 

 which mull take place. The fame consideration may be 

 applied to thofe affinities called eletlive. 



8th, A precipitate is fometimes effected by the mixture of 

 two faline fubftances which have ihe fame acid ; for in ft an ce. 

 by a mixture of the muriate of magnefia and the muriate of 

 lime. It is probable that two combinations are then formed, 

 one with an excefs of acid and a fmall part of the two bafes, 

 the other with the greateft part of the two bafes and a fmall 

 portion of acid. 



This efieet is analogous to what we have ohferved in 

 Art. IX. No. 3 ; but here it is the mutual affinity of the two 

 bafes which determines the precipitation. 



9th, We have feen in Art. VII. that heat, by increasing 

 the volatility of a fubftance, weakens its combination. This 

 caufe a&s no lefs in the complex than in the elective affi- 

 nities. It is a force added to thofe which a6f, and deter- 

 mines the union and the feparation of thofe fubftances which 

 have the greateft tendency to form a volatile combination. 



Whenever, therefore, it is defired to know what will hap- 

 pen, by expofing two falts to the action of heat, it is only 

 necefTary to examine whether one of the two bafes and one 

 of the two acids pofTefs a greater degree of volatility than the 

 remaining bate and acid; and we may be afturea that, on 

 applying a fuffieient degree of heat, the combination of the 

 molt volatile bafe and acid will be formed and fublimed, 

 while the more fixed bafe and acid will alfo remain com- 

 bined. Among the bafes, ammonia and the oxide of mer- 

 cury, and among the acids, the carbonic and muriatic, afford 

 feveral illuftrations of this truth. 



10th, Effiorefeence ought alfo to be considered as a force 

 which, in the complex affinities, may determine a combina- 

 tion pofiefling this property; and to this is owing the form- 

 ation of natron in the valley of the lake of Natron, and other 

 places where the fame circumftances occur. 



The obfervations which 1 have piefented to the Inftituteof 

 Egypt, which will form a fequel to the interefting difcovery 

 of the valley of the lakes of Natron, for which we are in- 

 debted to general Andreofli, prove that the circumftances 

 necefTary to the formation of natron are, 1. A land, which 

 contains much carbonate of lime; 2. Moifture; and, 3. The 

 prefence of the muriate of foda : I have alfo remarked, that 

 the ftalks of the reed, in a great degree., facilitate the produc- 

 tion 



