122 Conductivity of Aqueous Solutions. Part V. 



for the solvent alone, indicating that this solute does not volatilize appre- 

 ciably. The same result was obtained with hydrochloric acid. 



CONDUCTANCE OF THE WATER. 



A correction was applied in the case of the two salts (but not in that of 

 the two acids) for the conductance of the impurities in the water. This 

 will be fully described in section 51, in connection with the data upon 

 which it is based. 



INCONSTANT BRIDGE READINGS. 



No special trouble was encountered in the sodium chloride measure- 

 ments. It was observed, however, in working with the diluter hydro- 

 chloric acid solutions that the bridge readings at 18, and to a less extent 

 at other temperatures, shifted rapidly when the current was kept on, the 

 displacement being generally in the direction of increasing conductivity. 

 The shifting reached a limit in about three minutes, but on discontinuing 

 the current for a minute or two the reading returned to approximately its 

 original value. It was considered likely that this was due to the ejection 

 by the alternating current of solute which had been adsorbed by the lower 

 electrode. It was not permissible to adopt the final reading, since the ef- 

 fect of ejection would be to concentrate the solution within the cup; and 

 the initial reading could not be accurately determined. It was found that 

 the shifting of the reading was greater, the louder the tone of the induction 

 coil. A Nernst string interrupter, with low vibration frequency, was there- 

 fore substituted for the ordinary induction coil. The total shifting with the 

 string interrupter was much less, and it took place so slowly that no diffi- 

 culty was experienced in making a satisfactory reading. Except at the 

 highest resistances measured the minimum with this interrupter was very 

 good. 



In working with the sodium acetate and the 0.0005 normal hydrochloric 

 acid solution great difficulty was experienced, when either induction coil 

 was employed, in securing constant readings at 218, Cell i (see section 

 50) being then in use. Even after sufficient time had elapsed for the bomb 

 to acquire the temperature of the bath, successive readings made during a 

 half hour exhibited an irregular, somewhat oscillatory shifting through 

 several centimeters on the bridge in the direction of decreased conduc- 

 tivity. If instead of reducing the pressure in the air space originally to 2 

 cm. of mercury as had been the practice, the air was allowed to remain in 

 the bomb, the direction of shifting was reversed, these tests being made 

 with a 0.01 normal sodium acetate solution. It was not possible to find 

 an intermediate pressure which afforded constant readings. The effect of 



