186 PROCEEDINGS OF THE AMERICAN ACADEMY. 



V. Procedure for the Specific-Volume Measurements. 



To determine the specific volume of a solution at any temperature, 

 such an amount of solution is weighed into the bomh as will bring the 

 liquid level up onto the auxiliary electrode at that temperature. This 

 amount was determined by successive heatings with increasing volumes 

 of solution. 



A pipette of the form represented by Fig. 8 was made for each of 

 the temperatures 218°, 281°, and 306°. The stem is graduated between 

 a and b, and the capacity up to these points is roughly determined by 

 weighing. The volume of the pipette is made such that for 

 w ater or dilute solutions it will deliver the right amount into 

 the bomb when filled up to the point b. For more concen- 

 trated solutions the expansion is less, so that more of the 

 solution must be used. The graduations on the pipette serve 

 \ only as an indication of how much solution to take. The 



exact amount used is obtained by weighing the pipette filled 

 and then again after discharging. During the weighing the 

 tip is covered with a small test tube, c, which is held on by 

 N / the rubber band, d. 



The bomb is first dried out by rinsing it with alcohol and 

 ether. The residue left by the ether upon evaporation is 

 sufficient to affect the conductivity of the diluter solutions 

 employed, so that no attempt was made to determine the con- 

 ductivity of such solutions at the same time as their specific 

 Figure 8. volume. The solution is boiled to expel the air. This 

 increases the concentration slightly ; but this is of no conse- 

 quence if, as was usually the case, the experiment was made solely to 

 determine the specific volume. If it was also to serve for conductivity 

 measurements, the solution was boiled gently in a tall platinum' vessel 

 which was weighed with its contents before and after boiling. This gave 

 the loss of solvent during the operation. Knowing this and the amount 

 of solution originally present in the cylinder, the final concentration is 

 easily calculated. After weighing the solution in from the pipette, the 

 bomb is closed, and the air pressure reduced to 2 cm. Upon heating, 

 careful watch is kept of the readings with the auxiliary electrode to make 

 sure that too much solution has not been put in. After the conductivity 

 of the upper chamber has been constant long enough to show conclusively 

 that the temperature has become stationary and that the bomb is ab- 

 solutely tight (even the slightest leak being of course indicated by a 



A 



