CONDUCTIVITY OF AQUEOUS SUOLUTIONS.—McKAY. 349 
presence of chlorides, and with potassium ferrocyanide for iron. 
In none of these tests was any reaction observed. The solu- 
tions whose conductivities were measured range in the case of 
potassium sulphate from 1 to 0.1 gr.-eq. per litre and from 0.02 to 
0.0066, and in the case of magnesium sulphate from 2 to 0.4, and 
from 0.025 to 0.008 gr.-eq. per litre. All the determinations by 
Kohlrausch which lie within these limits agree with the writer’s 
within the latter’s limits of error, except the value for the solu- 
tion of magnesium sulphate of concentration 0.5, the conductivity 
of which, as measured by the writer, is 0.6 percent. less than the 
value given by Kohlrausch. This difference was found to hold 
in the case of four specimens of recrystallized salt, both Eimer & 
Amend’s and Merck’s. The error of the writer’s determination 
in this case night be 0.4 per cent. 
In the first attempts to prepare the double salt, the K,SO, 
and MgSO, were brought together in equimolecular, or nearly 
equimolecular proportions. In the case of the salt numbered I 
below the solution thus obtained was evaporated until erystals 
began to form. It was then allowed to cool to 75°C. and kept at 
a temperature varying from 60°C. to 75°C., until a large part of 
the salt had crystallized out. The crystals were dried on filter 
paper, and a portion heated in a platinum crucible to a dull red 
heat, until the weight was constant. The amount of SO, in the 
dry salt was then determined. The second specimen was crystal- 
lized out from a solution containing asmall excess of MgSO,, and 
was treated in a similar manner, except that the drying on filter 
paper was omitted. The third specimen was _ recrystallized 
according to a method given in its essentials in Dittmar’s Quan- 
titative Analysis. 87.1 grammes of powdered recrystallized 
K,SO,, together with 153.4 gems. of Eimer & Amend’s chemically 
pure MgSO,+7 H,O, which had not, however, been recrystallized 
by the writer, were dissolved in 350 grammes of hot distilled 
water. The solution was made up to about 645 grammes, and 
after it had cooled to 50°C, put in a porcelain basin and left 24 
hours. The crystals thus obtained were washed in pure water, 
powdered, and then dried on filter paper and by exposure to the 
