

SURFACE TENSION OF AQUEOUS SOLUTIONS. BARNES. 51 



float one could read to 0.1 cc. 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 pycno- 

 meter of the Ostwald-Sprengel form, holding about 22 cc. All 

 observations were made at 18 0. 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. 



