GOODWIN AND HASKELL. — CONDUCTIVITY OF SOLUTIONS. 403 



than 0.5 milligram, or 0.05 per cent in the case of the smallest por- 

 tion. In this way a series of solutions, usually varying in concentration 

 from about 0.0001 normal up to 0.001 or 0.002 normal, were prepared, 

 and their conductance measured. 



Several experiments were made to determine whether the conduc- 

 tivity of dilute acid solutions changed with time upon standing in the 

 covered conductivity vessel in the thermostat. The change upon stand- 

 ing over night amounted to only 0.1 per cent of the conductivity of a 

 0.0002 normal solution. 



In order to confirm the accuracy of the method, similar series of 

 measurements were made with potassium chloride solutions at the same 

 dilutions as in the case of the acids. The results, which are communi- 

 cated in the Section V, agree within 0.1 per cent with those obtained 

 by Kohlrausch and Maltby, in their very accurate determinations pub- 

 lished in 1900.* 



IV. Methods of Correcting for Impurities in Water at 

 Great Dilution. 



We have employed two methods for eliminating the influence of the 

 impurities in the water on the conductivity of tlie acid solutions. Both 

 of these involve the principle that the total effect of the acid and of the 

 impurities in the water on the conductivity of each other is already pro- 

 duced when a relatirely small quantity of acid has been added to the 

 ioater, after which further additions of acid remain unaffected by the 

 impurities. 



In the first method of computation this principle is applied in a di- 

 rect manner by simply subtracting the conductivity of a very dilute 

 acid solution from that of a more concentrated one, and regarding the 

 ratio of this difi'erence to the difference in the respective concentrations 

 as the equivalent conductivity of the acid at the higher concentration ; 

 that is, if Ki and /co are the conductivities at the concentrations q and Cg 

 respectively, Ci being a very small concentration, it is assumed that 



-; = Ac, the equivalent conductivity at the concentration Co.f 



* Wissensch. Abhandlungen d. phys.-technischen Reichsanstalt, 3, 157-227 (1900). 

 Zeitschr. phys. Clieni., 36, 750 (1901). 



t In tlie calculation of Af., it is necessary to apply a slight correction to the 

 observed conductance (/c/), since when the second portion of acid is added the 



