SURFACE TENSION OF AQUEOUS SOLUTIONS.—BARNES. 51 
float one could read to 0.1 ec. Corrections for the volume of the 
water contained between every two cubic centimetre marks 
were found and plotted on co-ordinate paper against the reading. 
The pipettes were all employed as much as possible in the same 
way, and none required less than 40 seconds to flow out. Two 
flasks holding a litre and a half litre respectively, were the only 
ones used. These were calibrated by the weight of water they 
held at 18° C. 
Measurement of Specific Gravity. 
The specific gravity observations were made with a pyeno- 
meter of the Ostwald-Sprengel form, holding about 22 cc. All 
observations were made at 18° C. To obtain this temperature it 
was necessary, after filling the pycnometer with the solution at 
about this temperature, to place it in the bath described below, in 
which the temperature remained at 18° C. for a considerable time. 
After remaining in the bath fifteen minutes or more the meniscus 
was adjusted to the mark. If the meniscus now remained 
stationary for a few minutes, the pycnometer was removed, 
carefully cleaned and dried, and then weighed. The barometer 
and thermometer readings in the balance case, where the air 
was kept as dry as possible by means of calcium chloride, were 
taken, and corrections applied for the buoyancy of air. The 
specific gravity of a certain solution of potassium chloride was 
found by this method to have the following values : 
(1) 1.04455 
(2) 1.04458 
(3) 1.04449 
(4) 1.04450 
Mean 1.04453 
Thus results which differed by about 5 in the fifth place of 
decimals from the mean value could be obtained. 
Measurement of Conductivity. 
The method employed by Kohlrausch with the alternating 
current and telephone was used. 
