2S0 Conductivity of Aqueous Solutions. Part VIII. 



quantity of some impurity a behavior analogous to that observed in the 

 case of silver nitrate by Noyes and Melcher. 



Phosphoric acid, which is only moderately ionized, shows a behavior 

 with respect to change with the concentration which is intermediate 

 between that of the largely ionized acids and salts and that required by the 

 mass-action law, the value of the exponent n in the concentration function 

 being 1.8-1.9. Its ionization decreases rapidly with rising temperature 

 (in 0.1 normal solution from 28.5 per cent at 18 to 17.5 at 100 and 11.5 

 at 156) ; but this does not seem to be accompanied by a closer conformity 

 to the mass-action law. Its ionization-constants calculated by that law 

 (which vary considerably with the dilution) are at 0.1 normal 11,400 X 

 10- fi at 18, 3,700 X 10" at 100, and 1,490 X 10~ 6 at 156, the values for 

 acetic acid and for chloracetic acid at 25 being 18 X 10 fi and 1,550 X 10 6 

 as determined by Ostwald. 



The interpretation of the results obtained with sulphuric acid is com- 

 plicated by the fact that the ionization doubtless takes place in two stages; 

 but it has been shown that it is possible to determine the hydrogen-ion 

 concentration within fairly narrow limits from the conductance alone, 

 without knowledge of the extent to which the separate stages occur. The 

 ratio of the hydrogen-ion to the total hydrogen of the acid is thus found 

 to vary in 0.08 normal solution from about 66 per cent at 18 to 48 at 

 100 and 35 at 306. Similar calculations of the hydrogen-ion concentra- 

 tion have been made in the case of potassium hydrogen sulphate. These 

 show that in 0.1 molal solution at 156 the hydrogen-ion concentration is 

 not more than 3 per cent; and this justifies the conclusion that the second- 

 ary ionization of sulphuric acid (into hydrogen-ion and sulphate-ion) in 

 its own moderately concentrated solutions is also insignificant at this tem- 

 perature and higher temperatures. Interpreted with the help of this con- 

 clusion, the conductivity data for the acid show that the primary disso- 

 ciation (into hydrogen-ion and hydrosulphate-ion) is about the same as 

 that of hydrochloric acid at temperatures between 100 and 300 ; and it 

 is reasonable to suppose that the same is true at lower temperatures down 

 to 18. With the help of this principle the ionization of the hydrosulphate- 

 ion at 18, 100, and 156 in the solutions both of the acid and acid salt 

 has been computed; the final results will be found in tables 118 and 119, 

 in section 97. This ionization is thus found to be large at 18 ; but it 

 decreases very rapidly with the temperature. Thus in a 0.1 molal potas- 

 sium hydrogen sulphate solution equal quantities of sulphate-ion and 

 hydrosulphate-ion are present ; while at 100 there is only 15 per cent, and 

 at 156, 4 per cent, as much sulphate-ion as hydrosulphate-ion in the solu- 

 tion. Only rough values of the ionization-constant of the hydrosulphate- 

 ion into hydrogen-ion and sulphate-ion can be given, since they vary very 



