138 MEMOIR OF DR. DALTON, AND 



compounded with a foreign body ; 2nd, that the point of 

 saturation is not changed ; and 3rd, that the power which 

 unites this portion which is added to the neutral salt, may be 

 much weaker than that which unites the same substance to 

 the same, at the point of saturation, without causing a con- 

 tradiction." 



Page 566. " I shall terminate this section by a short 

 resume of the principal characters, which are capable of form- 

 ing a methodic division of affinities, and which may have been 

 lost sight of in the course of the preceding discussions. 



" 1st. Two bodies of the same nature, whether simple or 

 compound, may unite and form a third, as homogeneous as 

 either of the two before the union. This is called affinity of 

 aggregation, 



** 2nd. Two bodies of a different nature, simple or com- 

 pound, may unite without undergoing any change in their 

 first composition, if they are compound. This is called affinity 

 of composition. 



" Two out of three bodies may shew a preference and com- 

 bine, leaving the third at liberty ; these bodies may either be 

 simple or compound, provided their composition does not 

 change, and they are found in a condition favourable to 

 contact. This is still affinity of composition ; whether the 

 three bodies have been put separately into the mixture, or 

 two been previously united, whilst the superior affinity of 

 the third has destroyed their union, by what is called pre- 

 cipitation. 



" Three or more bodies, exposed to contact, may unite in 

 such a manner as to form only one homogeneous mass. 

 This is nevertheless affinity of composition, although two only 

 unite at first, and a third is added to the first two, and so 

 on successively. 



«* 3rd. Two bodies incapable of combining, become so when 

 one or the other has either been decomposed or supercomposed. 



