124 Conductivity of Aqueous Solutions. Part V. 



INSTRUMENTAL ERRORS. 



In working with dilute solutions of hydrochloric acid it was found that 

 commutating the current from the secondary coil gave a difference of 

 reading of 0.1 0.4 mm. The coil was tested with known resistances 

 and found to show an asymmetric reading only with the higher resistances, 

 an error of 0.1 per cent or more being involved when the resistance ex- 

 ceeded 5,000 ohms. This error was corrected for, however, by taking 

 double commutated readings in all such cases and finding the mean. It 

 was found that commutating the telephone had no effect even with the 

 highest resistances used. 



In the measurement of very high resistances (those above 10,000 ohms) 

 the proximity of the induction coil to the bridge was found to have an 

 influence on the reading, if the distance was less than 40 cm. Such prox- 

 imity was therefore avoided. 



50. CONDUCTANCE-CAPACITY OF THE APPARATUS. 



The conductance-capacity was calculated from measurements made in 

 the bomb at 18 of the conductance of various known solutions of potas- 

 sium chloride and sodium chloride and from the values of the equivalent 

 conductance of these salts as given by Kohlrausch and Maltby.* 



In the course of the work three different values of the conductance- 

 capacity were used, corresponding to the changes made in the lower elec- 

 trode. In all the measurements made prior to April 4, 1904, the bomb 

 was used as it was left by Noyes and Coolidge, in which form it will be 

 designated cell i. On that date the platinizing was mechanically removed 

 from the electrode, which caused a slight change in the capacity, the new 

 value of which (cell n) was used in connection with all measurements be- 

 tween April 4, and June 25, 1904. The quartz cup was then removed from 

 the bomb and a cylindrical electrode substituted for the flat one. The new 

 conductance capacity (cell in) then obtained is that used in calculating all 

 the measurements made subsequently to June 25, 1904. 



The following table shows the actual conductance at 18 of the solutions 

 diminished by that of the water, and the conductance-capacities calculated 

 therefrom. The conductances expressed in reciprocal ohms are given in 

 the table multiplied by 10. The concentration is expressed in milli-equiv- 

 alents per liter at 18. The conductance-capacity is, as usual, the factor 

 by which the observed conductance must be multiplied to give the specific 

 conductance. Each of the measurements was made upon separate, freshly 

 prepared solutions. 



*Wissensch. Abhandlungen phys.-techn. Reichsanstalt. 3, 210 (1900). See also Lan- 

 dolt-Bornstein-Meyerhoffer, Tabellen, p. 744 (1905). 



