Section 102. Conductivity and Ionization-Constants. 289 



The final bridge reading was not recorded until it had become con- 

 stant, which it did in 15 - 30 minutes. It then remained constant, even 

 over night, in almost all cases ; but with a few solutions containing the 

 salt with an excess of ammonium hydroxide there was a slight progres- 

 sive increase in conductance, for which a small correction (never more 

 than 0.25 per cent) was applied, depending upon the time which had 

 elapsed before the reading and upon the temperature to which the cell 

 had been exposed. 



102. THE CONDUCTIVITY AND IONIZATION-CONSTANTS OF AMMONIUM 

 HYDROXIDE AND DIKETOTETRAHYDROTHIAZOLE. 



Tables 120 and 121 contain the results of the conductance measure- 

 ments with ammonium hydroxide and with diketotetrahydrothiazole. 

 The first column gives the temperature ; the second, the date ; the third, 

 the concentration in equivalents per liter of solution at the temperature 

 of the measurement ; the fourth, the conductance in reciprocal ohms as 

 actually measured in the conductivity vessel, multiplied by 10 6 ; the 

 fifth, the same diminished by the conductance of the water; the sixth, 

 the equivalent conductance (A) calculated by multiplying the values of 

 the preceding column by the conductance-capacity (0.17861 for the acid 

 and 0.17775 for the base) and dividing by the concentration given in 

 the third column and by 10 3 ; and the seventh, the ionization-constant (K) 



calculated by the expression K = - , r- and multiplied by 10 G . 



Ao(A A-) 



The values of A (the equivalent conductance for complete ionization) 



used in the calculation of the ionization-constant were derived as follows. 



That for the OH - ion at 18 was found to be 173.0 by subtracting Kohl- 



rausch's value* for the sodium ion (43.55) from Noyes and Kato's value 



for sodium hydroxide (216.5, see Part VI). That for the NH + 4 ion at 



18 was found to be 65.4 by subtracting Kohlrausch's value for chloride 



ion (65.44) from Sosman's value for ammonium chloride (130.9, see 



Part VII). In this way the value for ammonium hydroxide was found 



to be 238.4 at 18. Those for ammonium hydroxide at and 25 were 



obtained from the corresponding equivalent conductances of the NH + 4 



and OH~ ions at 18 by means of the temperature-coefficients for the 



conductivities of these ions derived by Kohlrausch.f The values so 



obtained are Anh 4 = 39.3, Aoh = 117.7 and A 0( nh 4 oh) = 157.0 at ; and 



A N h 4 = 75.9, Aoh = 194.7 and A 0(N h 4 oh) = 270.6 at 25. The A values 



for the acid at each temperature were obtained from those for its 



ammonium salt by subtracting the equivalent conductance of the NII + 4 ion 



*Sitzungsber. preuss. Akad. der Wissensch., 1901, 1026-1033. 



flbid., 1901, 10. These coefficients are : 



(A NH4 ) , = ( A N H4)is [1 + 0.0223 (t 18) -f 0.000079 (t - 18 )-} 

 (A 0H ) t = ( Aoh), 8 [1 + 0.0179 (t 18) + 0.000008 (t - 18)-] 

 (A H ) 1 =(A H )is [1 + 0.0154 (t- 18) -0.000033 (t 18) 2 ] 



