26G HISTORY OF CHEMISTRY. 



which have any disposition to combine, are united ; if there approaches 

 them a third, which has more affinity with one of the two, this one 

 unites with the third and lets go the other." He then states these 

 affinities in the form of a Table ; placing a substance at the head of 

 each column, and other substances in succession below it, according 

 to the order of their affinities for the substance which stands at the 

 head. He allows that the separation is not always complete (an im- 

 perfection which he ascribes to the glutinosity of fluids and other 

 causes), but, with such exceptions, he defends very resolutely and sue 

 cessfully his Table, and the notions which it implies. 



The value of such a tabulation was immense at the time, and is even 

 still very great; it enabled the chemist to trace beforehand the results 

 of any operation ; since, when the ingredients were given, he could see 

 which were the strongest of the affinities brought into play, and, conse- 

 quently, what compounds would be formed. Geoffrey himself gave 

 several good examples of this use of his table. It was speedily adopted 

 into works on chemistry. For instance, Macquer* places it at the end 

 of his book ; " taking it," as he says, " to be of great use at the end of 

 an elementary tract, as it collects into one point of view, the most 

 essential and fundamental doctrines which are dispersed through the 

 work." 



The doctrine of Elective Attractions, as thus promulgated, contained 

 so large a mass of truth, that it was never seriously shaken, though it 

 required further development and correction. In particular the cele- 

 brated work of Torbern Bergman, professor at Upsala, On Elective 

 Attractions, published in 1775, introduced into it material improve- 

 ments. Bergman observed, that not only the order of attractions, but 

 the sum of those attractions which had to form the new compounds, 

 must be taken account of, in order to judge of the result. Thus, 3 if we 

 have a combination of two elements, P, s, (potassa and vitriolic acid), 

 and another combination, L, m, (lime and muriatic acid,) though s has 

 a greater affinity for P than for L, yet the sum of the attractions of P 

 to m, and of L to s, is greater than that of the original compounds, and 

 therefore if the two combinations are brought together, the new com- 

 pounds, P, m, and L, s, are formed. 



The Table of Elective Attractions, modified by Bergman in pursu- 

 ance of these views, and corrected according to the advanced knowledge 

 of the time, became still more important than before. The next step 



2 Pref., p. 13. 3 El'ct. Attract., t>. 19. 



