350 ON THE CALCULATION OF THE CONDUCTIVITY OF 



air. The following table shows the proportions in which the* 

 two salts were brought together, and the percentage of S0 4 

 obtained by analysis of the salt freed from the water of crystal- 

 lization By theory the percentage should be 65.27 : 



Percentage of Difference per cent. 

 K 2 SO 4 MgSO 4 SO 4 from theoretical value.. 



1 1.... 1 64.31 -1.5 



II 1 1.038 65.00 -0.4 



III 1 1.13 65.47 +0.3 



The error in a single analysis might be 0.2 per cent. The- 

 constitution of the specimens used was determined from two 

 analyses. The salt used in the double salt determinations was, 

 the specimen III., and another portion of salt prepared similarly 

 to it and which showed the same excess of SO 4 . This excess was 

 probably due to the fact that the double salt was crystallized out 

 of a solution containing an excess of 13 per cent, of MgS0 4 , an 

 excess of which, however, is necessary to prevent the formation 

 of K 2 S0 4 crystals along with those of the double salt. 



Of the double salt solutions referred to in the tables below,, 

 those in italics were made up in the cell itself by the addition 

 of 5 c. c. of water each time in the case of the solutions above- 

 0.1 gr.-eq. per litre, the original quantity h'aving been 100 c.c. 

 The other solutions were made up outside the cell and allowed! 

 to remain for some time before their conductivity was 

 measured. To obtain equimolecular mixtures of the simple 

 solutions, two solutions of K 2 SO 4 and MgSO 4 were made up, 

 of nearly the same concentration. Each of these was carefully 

 analyzed, the difference being found to be 0.2 per cent. The 

 proper amount of water was then added to the stronger solution 

 to make the two equimolecular. Other solutions were made up 

 by diluting these, the same pipette and flask being used in each 

 case to dilute the K 3 S0 4 and MgSO 4 solutions to the same extent. 

 Mixtures of equal volumes were then made in order to obtain 

 equimolecular mixtures of solutions of the two salts. The con- 

 ductivities of these were measured within at most four hours, 

 after they had been made up. 



