Fractional Distillation and Its Application in the Concentration of the Heavy Isotopes of Oxygen and Hydrogen

Abstract

IN a previous communication¹ we described a convenient type of fractionating column suitable for the concentration of the heavy isotopes of oxygen and hydrogen in water. The glass assembly was efficient for comparatively slow distillations and was capable of producing valuable enrichments of O¹⁸ in sufficient quantities of water to be useful for tracer studies. A column 12 ft. in length and ¾ in. in diameter had efficiency equivalent to about 450 theoretical plates for a boil-up rate of 500 ml. per hour, and, to give an illustration of its performance, in twenty-four days of continuous distillation at atmospheric pressure it produced 500 ml. of water with nearly a three-fold enrichment of O¹⁸. As expected, the production of the desired isotopes is increased by operating the column under reduced pressure. Thus, a five-fold enrichment of O¹⁸ is obtained after six weeks of continuous distillation at 150 mm. pressure. A further increase results by periodically replacing the reservoir water (which becomes lighter during the course of an experiment) by fresh water. It is more convenient, however, to use the same stock throughout a run, and this has generally been our practice with this column.