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D. C. GRAHAME AND G. T.SEABORC [ C O N T R I B L T I O S FROM THE C I I E Y I C A I . LABORATORY O F TIiK
t:o1. 60
UNIVERSITY OF
CAI.IPORNIA
]
The Distribution of Minute Amounts of Material between Liquid Phases BY D. C. GRAHAME AND G. 'r. SEABORG It frequently happens i n chemical investigations that a knowledge of the behavior of very small amourits of material in solution, either aloiie or accompanied by larger amounts of other substances, becomes of considerable importance. Particularly in the use of radioactive substances as indicators for chemical investigations or in the identificatioii of newly discovered artificially prepared radioactive isotopes is it desirable ~ C know what chemical behavior may be expected of minute quantities of radioactive matter in the absence of appreciable amounts of its inactive isotopes. The work oi Fajans, Paneth, Haliri and others' has led to the formulation of rules concerning the adsorption or coprecipitatioii of minute amounts of material upon precipitates formed under various conditions. Studies of this sort lead to qualitative conclusions only and do not permit any very accurate prediction as to the behavior of untried substances. It seemed likely, on the other hand, that minute amounts of material would distribute themselves betweeii liquid phases in a simple manner owing to the absence of adsorptioii phenomena so characteristic of the solid phase. I t could not be foretold. of cour:w, whether the walls of the containiiig vessel or the dust particles inevitably present in the solution would exhibit sufficient adsorptioii of the microcomponent to infliicncc thc. cxpcrimeiital results.
I. Partition of Gallium Chloride between Ether and Hydrochloric Acid Experimental De&ils.--LCthcr (99.3%) i i a s dricti w i i h anhydrous calcium chloride and metallic sodiuiir. then distilled in a n all-glass still (b. 1). 34.4 :k 0.2') Hydrochloric acid, 0 ,Y. n'as distilled ill an ail-&?.s i t i l l and shaken with ether t o reiiio\v possible traces of gallium chloride. Cheinically pure zinc cliloride \vab dissolved in tj S hydrochloric acid and freed froin galliuiii by I-cpeatcrl extractions of gallium chloride w i t h frcsli etiicr p i e p a r d as above. l h e solution so preparcd war; t'Vd])tJrated to remove hydrochloric acid, rcdissolvcd in tloul)ly-distillcd water and clectrolyzcd between a carLori cat li,jtlc ai10 platinuin anode to give a thin deposit of galliuiii-frce zinc The zinc was bombardcd ill air with 8.0 &IC\. dcutcroiis froni the Berkeley cyt.lotron to Corm, among ot1it.r thiiigs. radioactive isotopes of ~ a l l h i i i . From t h e irircnsitv of 1 he (1) A swnuiur)' .%ridd i m ~ s a i b ~ofi tlirsc invustigarions is f o i i n r l Hahu's " A p p l i d I ~ , , ~ i i ~ ~ , l i ~ ,n' i i ~Corncil ~r.. I Ithaca. X , Y , 1931;
iii
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radioactivity produced (-lo-* millicuries of sixty-eight minute gallium) we estimate that the amount of gallium formed was about lo-'* g.* The .sample of zinc containing this gallium was dissolved in 6 N hydrochloric acid (prepared as above) and shaken with 25 cc. of ether, whereby most of tlic radio-gallium was extracted as gallium chloride. 'This ether estract was shaken several times with 6 N hydrochloric acid (saturated with ether) to remove traces of zinc chloride from the ether solution after which the distribution ratio of the gallium chloride remaining in the ether was determined in the following manner. To the ether solution in a cylindrical separatory funnel a n approximately equal volume of 6 N hydrochloric acid (saturated with ether) was added. The mixture was brought t o a temperature of 20.0 0.1' in a water thermostat and shaken thoroughly to establish equilibrium between the liquid phases. After the volumes had been marked, the aqueous layer was drawn off very carefully into a second separatory funnel and shaken again a t 20" with a n equal volume of ether already in equilibrium with 6 N hydrocliloric acid. The two ether cstracts thus obtained were evaporated to dryness on shallow copper trays of identical size and shape which could be placed in a reproducible manner under a Lauritsen type quartz fiber electroscope or under a thin-walled Geiger-bfiiller counter. In order to obtain a fairly uniform deposit o n the copper trays, a few drops of alcohol were added to the ether during the evaporation process and the solution,was rocked back and forth by hand during the final stages of the evaporation. Gentle heating hastened the evaporation, but the solution was not boiled. The ratio of the intensities of the radiations from the radioactive gallium on the trays gave a measure of the relative amourits of gallium chloride present in the two ether estracts. Prom this ratio and a knowledge of the voluriies of the ether a i d aqueous phwes, it was possible t i ) calculate by a meihod of successive approximations the distribution ratio of the galliuni chloride between the two liquid phases. Because of the estreme thinness of the deposits on the trays self-absorption of the radiation by [lie body of the sample did not need to be considered in most instanccs. In certain experiments, however, the amount of material present in the trays was sufficient to absorb an appreciable fraction of the &particles emitted by the saniplc. I n such cases the relative intensities were estimated with a Geiger counter under conditions such that only y-rays were detected. The counting rate was then practically indcpendent of the thickrirss of the samples over the range of thicknesses used. f
Results.- -'There are two known isotopes of gallium formed by the bombardment of zinc with deuterons, with half-lives of sixty-eight minutes ( 2 ) This estiinair ,fiIw t;ihrs i i i t n .iccoiint t h e fact tli;it other aiid riou-rarlii)activrl drv formed IsutvpPs ut ;.alliuni tr.icIioa
