218 MEMOIR OF DR. DALTON, AND 



39. " Some chemists, influenced by having found determi- 

 nate proportions, in several combinations, have frequently 

 considered it as a general law that combinations should be 

 formed in invariable proportions ; so that, according to them, 

 when a neutral salt acquires an excess of acid or alkali, the 

 homogeneous substance resulting from it is a solution of the 

 neutral salt in a portion of the free acid or alkali." 



" This is a hypothesis which has no foundation, but a dis- 

 tinction between solution and combination." 



42. " It follows, from what has been said above, that the 

 most powerful, as well as the weakest chemical action, is 

 exerted in the ratio of the reciprocal affinity of the substances, 

 and of the quantities within the sphere of activity ; that the 

 action diminishes in proportion to the saturation, and that 

 there is no point at which it determines the proportions, but 

 that the limits of these proportions in the combinations which 

 it forms, and those of its power, are to be sought for in 

 the forces which are opposed to it. Finally, two effects of 

 chemical action must be distinguished, that by which it pro- 

 duces a reciprocal saturation, and that which causes a change 

 in the constitution." 



47. " Hence it follows, that in the comparison of the acids, 

 the first object which will fix the attention is the power with 

 which they can exercise the acidity which forms their dis- 

 tinguishing character. Now this power is estimated by the 

 quantity of each of the acids which is required to produce the 

 same effect, that is to say, to saturate a given quantity of the 

 same alkali.'* 



Beautiful and ingenious as Berthollet's investigations into 

 affinity are, he, too, missed the line of thought which was to 

 produce the greatest discovery known to chemistry, but it was 

 not carelessly passed over. His inquiries had led him into 

 some very interesting qualities of bodies, the power of quantity 

 to overpower feebler quantities in certain cases, and the capa- 

 city of bodies to decompose others according to the nature of 



