I t remains to present data on the adsorption of labeled potassium palmitate on thin films of polysty'rauLE
l O j c (mules/l )
17
10'31' (moles/cm
1 17 7 34 4 68
9)
0.6 1.0 1.7
i 02 n 36 11 7 17 3
2.6 3.6 4 ,0
4.2 3.5
23 1
rene. The technique of making these ~neasurements is described in a previous section. Data are presented in Table 1 7 ; c = concentration of potassium palmitate. It is of interest that in this case, too, saturation of the interface occurs a t a concentration of soap considerably below the critical micelle concentration. Acknowledgment.-The authors desire to acknowledge the technical assistance of Mr. Frank Grosseibl, who made most of the surface tension measurements reported in the foregoiiig paper. Passa~c,S.J.
[CUSTRIUUTIOS FKOM TIlE I)EPARTMIEST O F CIIllMISTRT O F 1 I I E KSIVERSI'TY O F O R E G O N ]
The Ionization Constant of Metanilic Acid from 0 to 50" by Means of E.M.F. Measurements BY KAY31OND D. 1 I C C O U i\ND D. F. SWINEIIART RECEIVED APKIL19, 1954 The ionization constant of metanilic acid has been tleterminctl from 0 to 50' by the use of cells without liquid junction. T h e equation -log K = 1327.59/T 0.00281319T - 1.56331expresses the experimental dnta as a function of temperature in the above temperature range with :I standard deviation of 0.00054in -log K for eleven experimental points. An exceedingly small value of AS0 for the ionization reaction, -0.57 e.u. a t 26", is found.
+
Introduction The ionization constant of metanilic acid has been measured by several investigators. Of these investigations all but one1 are results of conductivity measurements and were interpreted without taking interionic attractions into account. The resulting values are as follows: Investigator rc x io: I , OC. Ostwald2 IYhite arid Jones3
~0yle4 Zollinger,
Biichler
and
IVittrver'
1.85 0.90 1.33
25 0 17
1.99
-1
2.62 2.11 7.24
35 2 ,i 23
I-InXCJ-IrSO:j-
+ EI
and the thermodynamic ionization constant expression
.I j
It has been shown by Carr and Shuttj from measurements of the change of dielectric constant with @Hof sulfanilic acid solutions that sulfanilic acid is a zwitterion. Considering that metanilic is even weaker than sulfanilic acid, it is reasonable to suppose the former acid also exists in solution as a zwitterion. Hence the ionization coilstant is for the reaction +HaIiCsH4S03- =
The cells were of the type Pt, Hz/Hnfet(ml), NaNet(mz), NaCl(ma)/;ZgC1-hg, where HMet and NaMet are metanilic acid and its sodium salt and m l , m? and m3 are molalities. By elimination of VZH YH+from the cell potential equation
-r
It is the object of this investigation to present accurate values of the ionization constant of metanilic acid determined over the temperature range 0 to 30" by the measurement of the electromotive force of cells without liquid ,junction following the general method developed by Harned and co-workers. (1) 13. Zollinger, W. Biichler and C . Wittmer, R c l z ' Chiifi. Rcln. 3 6 , 1711 (1053:. (2) X' Ostwald, Z p h y q i J ; ChpIfL., 3 , 408 (1889). (3) G. F. White and H. C . J o n e s , A m . Chent J ,44, 13) (1910) (4) hf. Boyie, J . Chem S , x , 115, 1.505 ( I S I S ) ( 5 ) \T Carr and 15' J S h u t t . 7'runs F i l ~ n d i i y,?
