288 



Conductivity of Aqueous Solutions. Part IX. 



lated from the densities of the solid acid and of the water or ammonium 

 hydroxide solution, under the assumption that no change in the total 

 volume occurs on mixing.* The concentration given in the tables below 

 is always that at the temperature of the measurement. 



The atomic weights used were those referred to oxygen as 16.00 as 

 given in the report of the International Committee for 1906. f All weights 

 were corrected for the bouyancy of the air. 



101. APPARATUS AND METHOD. 



The conductivity measurements were made 

 with a slide-wire bridge by the usual Kohl- 

 rausch method. The slide-wire was cali- 

 brated and the resistance coils were com- 

 pared with each other. The conductivity vessel used 

 was one of pipette form devised by Mr. G. A. Abbott 

 in this laboratory. It is shown in Fig. 19. It has 

 the advantages that the solution can be introduced into 

 it and kept in it entirely out of contact with the air, 

 that the electrodes are fully protected against change 

 in position, and that the vessel can be entirely immersed 

 in the thermostat. The capacity of the vessel was 

 about 25 c.cm. ; and the vertical electrodes were about 

 2 cm. square and 1.3 cm. apart. The electrodes were 

 used unplatinized in the measurements with the acid, 

 so as to reduce contamination; but were platinized in 

 the measurements with the better-conducting base and 

 salt. The conductance-capacity of the vessel was deter- 

 mined by measuring in it (when unplatinized) a freshly 

 \_yj prepared 0.002136 normal or (when platinized) a 

 0.0500 normal solution of potassium chloride,! and 



E" I Q 



allowing for the conductance of the water employed. 

 The vessel was immersed in well-stirred thermostats whose tempera- 

 ture was kept constant within 0.01. That at was maintained by a 

 mixture of water and finely crushed ice in large proportion. The ther- 

 mometers used were compared with the laboratory standard. 



*The density of the acid at 25 was found to be 1.673 by weighing a large excess 

 of it in a pycnometer under its saturated solution. That there was in fact no appre- 

 ciable volume-change on mixing was shown by direct measurements of the density 

 of known solutions of the acid and of its salt. 



tSee J. Am. Chem. Soc, 28, 1 (1906). 



$The actual conductances of these solutions in the vessel after allowing for the 

 conductance of the water were 0.0015095 and 0.03256 reciprocal ohms at 18, which 

 correspond to conductance-capacities of 0.17861 and 0.17775, respectively, using 

 Kohlrausch and Maltby's equivalent-conductance values. The same value was 

 obtained at the end of the measurements as at the start. 



