Section 97. Ionization of the Substances. 267 



97. IONIZATION OF THE SUBSTANCES AND ITS CHANGE WITH THE 

 CONCENTRATION AND THE TEMPERATURE. 



Tables 114 and 115 contain the values of the ratio 100 A/A for the sub- 

 stances for which the equivalent or molal conductances are given in 

 tables 108 and 109. This ratio doubtless represents approximately the 

 percentage ionization in the cases of nitric and phosphoric acids, and 

 almost certainly also in the case of barium hydroxide ; for the second 

 hydrogen of phosphoric acid has been shown by the work of Mr. G. A. 

 Abbott* to be less than 0.05 per cent ionized at 18 at even 0.001 molal 

 concentration ; and the equivalent conductance of barium hydroxide 

 behaves at all temperatures so entirely like that of neutral uni-univalent 

 and unibivalent salts that it is hardly probable that any considerable 

 quantity of an intermediate ion like BaOH + exists. In the case of sul- 

 phuric acid, two sets of ratios separated by a dash are given in table 111; 

 the first one is 100 times the ratio of the equivalent conductance (A) of 

 the acid at the concentration in question to the sum of the equivalent 

 conductances of the hydrogen and sulphate ions (Ah + Aso 4 ), for which 

 sum the values were given in tables 109 and 110 ; the second one is 100 

 times the ratio of the equivalent conductance A to the sum of the equiva- 

 lent conductances of the hydrogen and the hydrosulphate ion (Ah + A-hso 4 ), 

 for which sum values equal to the A values for acetic acid were taken, 

 it being assumed that the latter ion has the same equivalent conductance 

 as the C 2 H 3 2 ~ ion, whose molecule consists of nearly the same number 

 of atoms. These two ratios represent the limits between which must 

 lie the percentage of the total hydrogen of the acid which exists in the 

 state of hydrogen-ion in the solution ; for if the acid dissociated wholly 

 into 2H + -\- S0 4 ~, this percentage would have the first value, and, if wholly 

 into H + and HS0 4 ~ the second value.f The value of the percentage ioni- 

 zation would evidently be the same as the first value if the acid dissociated 

 only in the first way, and twice the second value if it dissociated only in 

 the second way. 



Reference is here made to a research executed in this laboratory, but not yet 

 published. 



fThis will be evident from the following considerations. The specific conductance 

 t. of the solution is given in the two cases by the expressions 



l = ChAh -\- 2CSO4ASO4 and l = ChAh -f- ChsOiAhso* 



where the large C's represent molal concentrations ; or since Cn = 2CSO1 in the first 

 case and Ch = Chso* in the second, also by : 



l = Ch(Ah + Aso 4 ) and l = Ch(Ah -f- AhsoO ', 



from which by substituting for L its value cA where c is the equivalent concentration 

 of the acid, we obtain : 



Cn A and C 5= A 



Ah -f- A so 4 c Ah -\- Ahso 4 



