ANALYTICAL EDITION
March 15, 1935
20 per cent as the most convenient concentration; 0.25 ml. is theoretically sufficient when the volume of the reagents is 0.3 ml., but 0.4 cc. is taken when the reagent volume is less than 0.3, and 0.5 ml. when it is above. 7. Results obtained on the same water by the author have varied by ==0.007ml. of oxygen per liter. The accuracy is sufficient to warrant calibration and correction of the 2-ml. buret employed, as errors on these burets up to 0.01 ml. are not uncommon. A comparison of the absolute values for distilled water a t different temperatures with Fox's (1) tables revealed a systematic discrepancy of 1 per cent which has to be added to the titration results. A similar discrepancy has been observed before (2), but an explanation has not, so far, been found. CONCLUSIONS The method described was worked out mainly for biological purposes, but should also be useful industrially for the determination of oxygen in deaerated water. A serious source of error in the Winkler titration of water with a very low oxyaen content is the raDid absorwtion of air from the atmosphere. This error is counteracted, but cannot be abolished,
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by taking very large samples. I n the syringe method here described any possibility of contamination with air is excluded. When the amount of oxygen is below 0.5 ml. per liter there is no danger of loss of iodine, the buret only is required for the titrations, and the corrections for final volume and for oxygen in the reagents can be combined.
SUMMARY By the use of 10-ml. syringe pipets for the Winkler determination of oxygen in water, contamination with air from the atmosphere can be completely avoided. The accuracy can be increased a t least to *0.007 ml. of oxygen per liter, by avoiding loss of iodine and by corrections for the final concentration of iodine and for oxygen in the reagents. LITERATURE CITED (1) F ~Landol&B~rnstein, ~ , 5. ~ ~ fI,l p.. 715. (2) Jacobsen, Medd. Kommiss. Havunders$gelser Series Hydrografi I, No. 8 (1905). (3) Van Weekbzad*301 No. 2o (1933). (4) Yoder and Dresher, Combustion, April, 1934. R ~ C I ~ I VSeptember BD 18, 1934.
Fluorescence of Gaseous Acetone as a Test for Traces of Oxygen GLENN H. DAMON, Michigan College of Mining and Technology, Houghton, Mich. N A RECENT investigation by Damon and Daniels (1) it was noted that the photolysis of pure acetone vapor was
I
accompanied by a relatively intense green fluorescence. However, when even a trace of oxygen was present in the reaction cell, the fluorescence was a faint blue instead of green. It was also found that a sharp change in color from blue to green took place when the irradiation was continued for a period of time, roughly dependent upon the amount of oxygen present in the cell. This change in fluorescence suggests the possibility of its use as a sensitive semi-quantitative test for traces of oxygen. A method for the detection of traces of oxygen in samples of various gases should have a wide range of application, provided the gases with which the oxygen is mixed have no effect on the fluorescence of the acetone. Qualitative tests (1)show that nitrogen, hydrogen, carbon monoxide, carbon dioxide, chlorine, ethylene, methane, ethane, ethyl ether, and water have no effect on the fluorescence of pure acetone vapor. The time for the color change from blue to green was not materially changed by the addition of the above-mentioned gases.
s.,
length less than 3000 but the 3130 1.line of the mercury arc is transmitted with sufficient intensity for this test. In order to observe the fluorescence change, the reaction cell must be either in a dark room or in some type of enclosure which can be made relatively dark. hfAX1hfUR.Z SENSITIVITY O F
The maximum sensitivity of the fluorescence test for oxygen is determined by introducing known quantities of air into a cell containing pure acetone vapor. Air is sealed into a thin glass capillary tube, I, of known volume. The side container, H , is then sealed onto the main cell at G. Liquid acetone is placed in E and the entire system evacuated until most of the liquid acetone is evaporated and all air removed.
APPARATUS The apparatus is relatively simple and inexpensive. Figure 1 shows the essential materials for this work. Auxiliary apparatus for the purification, storage, and transfer of gases may be required. A capillary quartz mercury vapor lamp ( d ) , A , is the most satisfactory source of ultraviolet light, but a commercial lamp was found to give sufficient intensity for the test, and has the advantage of a more uniform intensity over a long period of time. A Corning Red Purple Corex No. 986 light filter, B, satisfactorily cuts out the visible light in the mercury arc. C is a 6-cin. quartz focusing lens (f = 10 em.). The reaction cell, D, is made from a round-bottomed Pyrex flask. Pyrex glass cuts out all radiation of a wave
TEST
FIGURE 1
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INDUSTRIAL AND ENGINEERING CHEMISTRY
The cell is sealed off a t P and placed in the water bath, where the pressure of the acetone vapor is raised to and kept at approximately one atmosphere. The appearance of a green fluorescence on irradiation proves that the cell is free from all oxygen except that in the capillary. The oxygen is introduced by removing the cell from the water bath and breaking capillary I by striking it against the bottom of container H . The sensitivity of the test is then determined by the time of irradiation required for the reappearance of the green fluorescence. Table I shows typical results using a capillary arc lamp. Variations in the intensity of the incident light and in the measurement of such small quantities of oxygen prevent the test from being rigidly quantitative, but the data show that the test is sensitive to approximately one micromole of oxygen. TABLE I. S~NSITIVITY OF FLUORESCENCE TEST Test No. Volume of 02 (S.T. P.), cc. Time t o green fluorescence, min. Partial pressure of 02,mm. Molecules Oz X 10-17
1 0.094 12
0.031 25.4
2 0.020
5 0.07 6.7
3
0.006 2
0.02 1.6
4
0.003
