The promising micromethod of Unterzaucher for the direct determination of oxygen in organic compounds has been investigated. The procedure involves pyrolysis of the compound in a stream of nitrogen and conversion of all the oxygen in the pyrolysis products to carbon monoxide over carbon at 1120°C.The carbon monoxide is oxidized to carbon dioxide by iodine pentoxide, and the equivalent amount of iodine liberated is determined titrimetrically. A furnace meeting the high-temperature requirements is described. Criteria are presented for the selection of carbon which gives quantitative conversion of the oxygen to carbon monoxide, and iodine pentoxide for quantitative oxidation of the carbon monoxide.The results obtained to date in this laboratory show over-all precision and accuracy somewhat less than those now obtained in carbon and hydrogen analyses. The method, however, possesses several outstanding advantages over other methods for oxygen determination, in that the apparatus is somewhat less elaborate, the presence of other compounds, such as sulfur, nitrogen, and halogens, has no effect on its applicability, and catalyst poisoning does not present a problem.ALTHOUGH oxygen is one of the most commonly occurring il constituents in organic compounds, there is, at present, no entirely satisfactory method for its direct determination. The lack of such a method is clearly emphasized in the recent excellent review by Elving and Ligett ($), who present a critical examina-

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topic mixtures as test liquids, and indicated that preliminary experiments had been successful.Hawkins suggested a mixture of ethylbenzene and chlorobenzene as an ideal test mixture for columns with up to 80 plates, and also for tests a t both atmospheric and subatmospheric pressures.Its relative volatility ranges from 1.10 a t 760 mm. to about 1.12 at 20 mm. of mercury pressure. The use of an n-heptanemethylcyclohexane mixture a t reduced pressures was also suggested.F. E . Williams of Hercules Powder Go. pointed out the lack of test mixtures composed of compounds other than hydrocarbons. Rossini felt this was because hydrocarbons were more easily obtained in the pure state than other types of compounds. INTERPRETATION OF DATAWilliams pointed out the complexities of analyzing break cuts to obtain over-all composition, and the desirability of being able to calculate composition directly from the boiling point or refractive index curves. Schoenberger recommended the use of the equal-area cut-point method for low temperature distillations, but also indicated this method had definite limitations. Rossini observed that from accurate boiling points and vapor pressuretemperature curves it is possible to calculate the boiling point of an equimolar mixture and thus establish the cut point. The additional difficulties which result from the presence of a third component during the break were noted.Hawkins described the calibration of columns with known mixtures, in order to obtain arbitrary correction factors for locating cut points and account quantitatively for the material subjected to analytical distillation.

Lithium greaseLess than 0.099 0.1 0.103 stopcocks should not be used in the direct path of the distilling vapors, as they will hold, by capillary action, part of the first water-rich distillate, and complete recovery of water will not be accomplished.

Coil and ring gas burners are described which fulfill the requirements of the thermal decomposition method for the direct determination of oxygen in organic compounds. The coil burner is designed for pyrolyzing the sample at 900°to 1000°C .; however, it is capable of producing a temperature of 1300°t o 1350°C. inside the reaction tube. The ring burner is designed to provide a temperature of 1100°C. near the end of the furnace used for conversion of the pyrolysis products to carbon monoxide. These gas burners have also been found useful in other microcombustion methods of ultimate analysis. The burners, which utilize a mixture of propane gas and air, are inexpensive, heat and cool the reaction tube rapidly, and provide a uniform distribution of heat around the tube. INTHE thermal decomposition method for the direct determination of oxygen in organic compounds, first proposed by Schiitze (2), the substance is py'rolyzed in a clear quartz tube in a stream of pure nitrogen at a temperature of 900°to 1000°C.

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