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 SO, 
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. 
K2S04 Mgs04 SO4 from theoretical value. 
tre Pa eee Ber. x le Meveie sss OM DIL i yous ote ak eee ae 
TEN acre cece ae EROS. tec xc. 65.00...0..% ~—OM 
iN DAR eens Sins el Spee MSc che o Ps SOOM ene. 2 aap ee ees 
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 ITI., and another portion of salt prepared similarly 
to it and which showed the same excess of SO,. 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 MgSQg, an. 
excess of which, however, is necessary to prevent the formation 
of K,SO, 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 having been 100 ce. 
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,SO, and MgSO, 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,SO, and MgSO, 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. 
