E. T. McGuinness and K. S. Clarke Seton Hall Universitv South Oronge, New Jersey 07079
( 1
Preparation and Standardization of Constant Boiling Hydrochloric Acid
The prcparatiou of a standard solution of hydrochloric acid by azeotropic distillation is a thoroughly investigated and document~edprocedure (1-9). The method oflers distinct advantages over the titrimetric standardization of a separately prepared sample of hydrochloric acid. References to the method in various textboolrs (10-14) usually include a tabular citation of the original data of Foulk and Hollingsworth (2),Hulett and Bonner (I), or Ronner aud Wallace (6) relating operating pressure to system composition. Since the azeotrope composition is relatedonly to the single variable of syst,empressure and the control of this pressure to within 0.2 mm of mercury is'casily maintained, we have found it more convenient to relate the azeotrope compositiorl to the system pressure in terms of a calibration curve when carrying out the distillation. When the data of I'oulk and Hollingsworth (2) and Ronrier and Titus (5) is represented graphically all calculations pertaining to the HCl concentration in the aseotrope can be made from this graph for any pressure setting
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Journal of Chemiml Edvcofion
between 730 and 770 mm Hg. Since the system pressure is readily calculated from any manometer setting of convenience it becomes a simple matter to exploit this method on a routine basis. Experimental Design
Continuous control over the operating pressure is maintained by joining a vacuum system consisting of a water aspirator, 20-1 ballast hoitle, and a benzyl benzoate or a-bromonaphthalene filled manometer to the distillation apparatus. The vacuum system described by Daniels, et al., (15) can be used for this purpose. We prefer to operate below ambient pressure with a level differencein manometer fluid between 40-90 mm. We have found it convenient to use a Iiontes No. Ii-54400 (Kontes Glass Co., Vineland, N.J.) distilling receiver mounted with four 300 ml flasks (I
