HISTORY OF THE ATOMIC THEORY. 155 



In agreement with this, he finds that the quantity of acid 

 necessary for dissolving certain weights of metals, differs with 

 each metal, and the amount which one metal precipitates from 

 the solution, differs with each metal. This was promising fair 

 for discovery ; and in the first table we have the amount of 

 various metals needed to precipitate 100 of silver, in fact, a 

 table of atomic weights, if he could have seen it, although 

 imperfection in experiment rendered it difficult, and the law 

 seemed very intricate. 



He drew the conclusion that some acids dissolve metals 

 with more oxygen in their oxides than others, when he says, 

 1 00 of silver are reduced by 3 1 of copper in nitric, and 30 of 

 copper in sulphuric acid. This helped to lead him wrong. 



He seems to have most naturally thought that it would be 

 needful to find the relation of the oxygen in a metallic oxide 

 to that in every other, and was naturally surprised at the great 

 labour needed. We know that this would be a most compli- 

 cated relationship, and that the oxygen is constantly changing 

 its per centage relation in every compound, to such an extent, 

 that it would be impossible to follow it without constant 

 recurrence to its atomic weight. We may look on this inquiry 

 of Bergman as a search, acute although unsuccessful after that 

 last step in simplicity. 



He gives a valuable discovery in the establishment of the 

 permanence of the amount of oxygen in precipitated oxides, 

 the very foundation of analysis, and an important step towards 

 the knowledge of permanence of constitution in all substances 

 whatever. That the numbers need correction, need hardly 

 be remarked. 



At the same time it seems to be beyond doubt that he did 

 not grasp with great clearness the doctrine of permanent con- 

 stitution, or he would scarcely have made these remarks on 

 neutral salts receiving a distinct excess of acid. Any indefinite 

 iimount added, becomes a mixture only. 



He extended the tables of attraction to a great length, 



