39° POPULAR SCIENCE MONTHLY. 



very great. But an inspection of the numbers of Kohlrausch and 

 others for the conductivity of the acids and bases, compared with the 

 measurements of Berthelot and Thomsen on their relative strength 

 with regard to their chemical effect, showed me that the best conduct- 

 ing acids and bases are also the strongest. I was thereby led to suppose 

 that the electrically active molecules are also chemically active. On 

 the other hand, the electrically inactive molecules are also chemically 

 inactive. In this connection I would mention the remarkable experi- 

 ments of Gore, which were easily explained by the new point of view. 

 Concentrated hydrochloric acid, free from water, has no action on oxides 

 or carbonates. Now this hydrochloric acid is almost incapable of con- 

 ducting the electric current, whereas its aqueous solutions conduct very 

 well. The pure hydrochloric acid contains, therefore, no (or extremely 

 few) active molecules, and this agrees very well with the experiments 

 of Gore. In the same way we explain the fact that concentrated sul- 

 phuric acid may be preserved in vessels of iron plates without destroy- 

 ing them, whereas this is impossible with the diluted acid. 



An unexpected conclusion may be deduced from this idea. As all 

 electrolytes in extreme dilution are completely active, then the weak 

 acids must increase in strength with the dilution, and approach to the 

 strength of the strongest acids. This was soon afterwards shown by 

 Ostwald to agree with experiments. 



The Norwegian natural philosophers, Guldberg and Waage, had 

 developed a theory according to which the strength of different acids 

 might be measured as well by their power of displacing another acid 

 in solutions as by their faculty to increase the velocity of chemical 

 reactions. Therefore, we may conclude that the velocity of reaction, 

 induced by an acid, would be proportional to the quantity of active 

 molecules in it. I had only a few experiments by Berthelot to demon- 

 strate this proposition, but in 1884, Ostwald published a great number 

 of observations that showed this conclusion to be true. 



The most far-reaching conclusion of the conception of active mole- 

 cules was the explanation of the heat of neutralization. As this is 

 much more easily understood by means of the theory of electrolytic 

 dissociation, I anticipate this for a moment. According to this theory 



strong acids and bases, as well as salts, are at great dilution (nearly) 



+ - 



completely dissociated in their ions, e. g., HC1 in H4- CI, NaOH in 



+ - + - 



Na -f- OH and NaCI in Na -j- CI. But water is (nearly) not disso- 

 ciated at all. Therefore the reaction of neutralization at mixing a 

 strong acid, e. g., HC1 with a strong base, e. g., NaOH, both in great 

 dilution, may be represented by the following equation: 



or, 



(H + CI) + (Na + OH) = (Na + CI) -f HOH; 



