April, 1936
COMMUNICATIONS TO THE EDITOR
693
THE PHOTOCHEMICAL FORMATION OF ETHYLENE IODIDE IN SOLUTIONS OF CARBON TETRACHLORlDE Sir :
oxygen from Lake Michigan water with the same hydrogen. This difference in density Dole (private communication) has since revised to 6.0 p. p. m. Morita and Titani [Bull. Chem. SOC. Ethylene iodide, which decomposes photo- Jafian, 11, 36 (1936) J comparing waters made chemically when exposed to the 303 and 313 from essentially pure protium report a difference mp mercury lines [THIS JOURNAL,57, 2411 of 8.0 p. p. m. due to the difference between at(1935)] and undergoes an iodine sensitized de- mospheric oxygen and water oxygen. We have composition at wave lengths of 436 to 579 mp found in this Laboratory differences of 5.8 and 6.2 [Dickinson and Nies, ibid.,57, 2382 (1935)], has p. p. m. in two experiments in which we have combeen found to be formed rapidly when solutions pared the densities of protium oxide from atmosof ethylene and iodine in carbon tetrachloride pheric oxygen with protium oxide from water are exposed to red light. A tungsten lamp with oxygen. Urey and Greiff [THISJOURNAL, 57,325 a Corning Filter No. 241 having maximum (1935) ] calculate for the reaction transmission at a wave length of ca. 700 mp was 02'6 2HaO'S (I) = 0 2 * 8 2H20'6 (1) used. Solutions containing iodine were thor- an enrichment factor 1.01at 0'. This corresponds oughly shaken in an all-glass apparatus at 25' to a water density difference of not more than 2.0 under a constant pressure of ethylene. All air p. p. m. since the enrichment factor diminishes was removed from the system by evacuation while with increasing temperature. the solution was frozen with a carbon dioxidePart of the difference between these figures may alcohol mixture. The rate of disappearance of be explained if one assumes that the atmosphere iodine was determined by light absorption. No is in equilibrium with the ocean in respect to oxymeasurable dark reaction occurred over periods gen isotope concentrations. We find that Lake of thirty-six hours. The rate of the reaction was Michigan water is heavier than Cambridge tap dependent on the pressure of ethylene and fell off water by 0.4 * 0.3 p. p. m.-a negligible differwith decreasing concentrations of iodine. Since ence. Gilfillan 56, 406 (1934)] reports that the efficiency of formation of iodine atoms from ocean water is 2.3 p. p. m. heavier than Camexcited iodine molecules may be small at X 700 bridge tap water. We have found a difference of mp (although the falling off in this efficiency with 1.8 p. p. m. [ib.id., 56, 1650 (1934)l. Thomson, increase in wave length is not as great (Dickinson Wirth and Utterbeck's results [ibid., 57, 400 and Nies, Zoc. cit.) as was formerly thought) the (1935) ] indicate that ocean water in general is not observed photoiodination a t 700 mp may possibly more than 1.7 p. p. m. heavier than their fresh proceed through the action of excited iodine mole- water. cules, whereas the photo-decomposition yields ioFresh water, being essentially a distillate from dine atoms and the sensitized decomposition pro- the ocean, is presumably lighter because of the ceeds through the action of iodine atoms. This greater volatility of water containing the lighter mechanism may obtain in the photoiodination of isotopes of hydrogen and oxygen. Although the butene-1 by incandescent lamps as reported revapor pressures given by Wahl and Urey [ J . cently by Forbes and Nelson [THISJOURNAL, 58, Chem. Phys., 3, 411 (1935)l indicate that more 182 (1936)]. than half of the change in density occurring when DEPARTMENT OF CHEMISTRY ROBERTE. DERICHT normal water is evaporated is due to separation of UNIVERSITY OF ROCHESTER EDWIN0. WIIC the oxygen isotopes, yet it is improbable that more ROCHESTER, NEWPORK RECEIVED FEBRUARY 17, 1936 than 1 p. p. m. of the density difference between ocean water and fresh water is due to the oxygen isotopes. AN EXPLANATION OF THE RELATIVELY LARGE It seems improbable that either the density CONCENTRATION OF 0l8IN THE ATMOSPHERE measurements of the theoretical calculations are Sir: sufficiently in error to account for the remaining Dole [THISJOURNAL, 57, 2731 (1935)J finds in difference of 3 p. p. m. The conclusion to which preliminary experiments that water made by com- this leads, namely, that the atmosphere is not in bining atmospheric oxygen with hydrogen is 4.6 equilibrium with the waters of the globe with rep. p. m. heavier than water made by combining spect to its content of oxygen isotopes, is less sur-
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