106 Studies on Solution. 



the cross-piece, held vertically with the regulating finger on the opposite 

 end of the cross-piece. The control finger is maintained throughout the 

 operation at this opening and the danger of contamination by suction 

 is removed. A tube filled with a mixture of calcium chloride and 

 soda lime is inserted in the rubber tube leading from the glass stop- 

 cock on the base of the T to the mouth, for obvious reasons. The 

 50 c.c. burettes adopted were calibrated at 2 c.c. intervals by weight. 



In order to titrate with phenolphthalein in an atmosphere free 

 from carbon dioxide the following apparatus was constructed, partially 

 as suggested by Hendrixson: 1 A carboy was connected to an ordinary 

 tire pump and served as a gas reservoir. The air was led through 

 three wash bottles, the first containing concentrated potassium hydrox- 

 ide solution, the second a more dilute solution, and the third pure 

 water. The titration was effected in an Erlenmeyer flask closed with 

 a rubber stopper, which in turn was fitted loosely around the burette 

 tip, serving in this way as a vent for the stream of air passed slowly 

 through the solution. 



The difficulty in desiccating our acids when once purified was 

 solved by means of a vacuum drying-oven designed by Dr. Davis and 

 constructed with the help of the authors (see Chapter II). In this 

 apparatus the lamp heating-unit maintained a temperature of 65 

 and an ordinary suction-pump kept a reduced pressure of 70 to 80 mm., 

 so it is easily seen that with the added help of a strong dehydrating 

 agent, such as sulphuric acid or phosphorus pentoxide, all traces of the 

 crystallizing solvent could be removed, since water boils at about 47 

 at this pressure. In proof of this practically all the organic acids 

 titrated theoretically. 



PROCEDURE. 



The sodium ethylate was standardized by titration with N/10 

 HC1 in a carbon-dioxide-free atmosphere, as described previously. 

 When the ethylate was standardized, the organic acid from which 

 the salt was to be made was weighed out in quantity sufficient to give 

 100 c.c. N/10 salt solution and this weight was confirmed by titration, 

 which showed a very general concordance, giving added proof of the 

 purity of the acids. In dealing with very deliquescent substances, as 

 trichloracetic acid for example, we weighed by difference, making ap- 

 proximate standard solutions rather than exactly N/10 strengths; but 

 even in this case we obtained confirmation of our work. The non- 

 deliquescent, crystalline acids were weighed on a watch crystal, the 

 deliquescent ones in glass-stoppered weighing bottles; but in both cases 

 the acids were washed through a funnel into the 100 c.c. measuring 

 flasks with conductivity alcohol and made up to mark at 25. Several 



'Journ. Amer. Chem. Soc. 37, 2352 (1915). 



