558 Professor Svante Arrhenius [June 3, 



this agrees very well with the experiments of Gore. In the same way 

 we explain the fact that concentrated sulphuric acid may be preserved 

 in vessels of iron plates without destroying them, whereas this is im- 

 possible 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 Berth elot to 

 demonstrate 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 

 molecules was the explanation of the heat of neutralisation. 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. HCl in H + CI, 



NaOH in Na + OH and NaCl in Na + 01. But water is (nearly) 

 not dissociated at all. Therefore the reaction of neutralisation at 

 mixing a strong acid, e.g. HCl with a strong base, e.g. NaOH, both 

 in great dilution, may be represented by the following equation : 



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

 or, 



H + OH = HOH. 

 The whole reaction is equivalent to the formation of water out of 



both its ions, H and OH, and evidently independent of the nature of 

 the strong acid and of the strong base. The heat of any reaction 

 of this kind must therefore always be the same for equivalent quan- 

 tities of any strong acids and bases. In reality it is found to be 

 13,600 cal. in all cases. This thermal equality was the most pro- 

 minent feature that thermo-chemistry had discovered. 



It was now asked in what resj)ect the active state of the electro- 

 lytes differs from the inactive one. On this question I gave an answer 

 in 1887. At that time van't Hoff had formulated his wide-reaching 

 law that the molecules in a state of great dilution obey the laws that 

 are valid for the gaseous state, if we only replace the gas-pressure 

 by the osmotic pressure in liquids. As van't Hoff showed, the osmotic 



