34 



OSMOTIC PRESSURE OP AQUEOUS SOLUTIONS. 



the following tabulation of data taken from the record of a single 

 manometer (No. 9). The meniscus correction (double) in this instru- 

 ment is 0.17 calibration unit, and the volume of the nitrogen under 

 standard conditions of temperature and pressure is 454.14 calibration 

 units. The temperature in all cases is 25°. Column I in Table 1 gives 

 the weight-normal concentration of the solutions; II gives the observed 

 pressure in atmospheres; III shows the volumes of the compressed 

 nitrogen reduced to standard temperature; IV, the corrections in 

 fractions of an atmosphere for the double meniscus; V, the relative 

 osmotic pressures, the pressure of the 0.1 normal solution being taken 

 as unity; and VI, the relative corrections for meniscus, the correction 

 for the 0.1 normal solution serving as the unit. 



Table 1. 



Particular attention is called to columns V and VI, where it will be 

 seen that, while the osmotic pressure increased a little over ten-fold, 

 the value of the meniscus correction increased nearly 88-fold. Ex- 

 pressed in heights of a mercury column, the correction for meniscus 

 in the case cited in the table increases from a value of 2.4 millimeters 

 to one of 211.5 millimeters. 



The method of obtaining the meniscus correction which is given 

 above is believed to be entirely correct in principle. Nevertheless it 

 has been found, in applying it, that the calculated volume of the 

 meniscus is always less than it would have been if the form of the 

 meniscus were truly spherical, as it is generally assumed to be. The 

 experimental correction is usually just about three-fourths that calcu- 

 lated from the supposed spherical form of the meniscus. The difference 

 may be due to unavoidable errors in reading the length of the short 

 calibrating threads. If these are always read "too short," the obvious 

 result would be a too small correction for the meniscus. However, 

 the error, if error it is, is not of a cumulative character. Moreover, if, 

 in calibration, one reads habitually "too short," he will repeat the 

 offense in reading pressures. For these reasons, it is believed to be 



