Document Xz1NdXEBJ23ODBNEkXKZp2B0g

SILVERMAN-HUSAIN--NITROGEN OXIDE-ARC WELDING 139 Total fume samples were obtained with the sampler described by Silverman and Ege.6 Oxides of nitrogen were collected simultaneously in a pair of evacuated gas sample flasks connected in series. One flask was analyzed for nitrogen dioxide and the other for total oxides. In order to determine nitric oxide (NO), the gas sample flasks were followed (experiments 4, S and 6) by two freezing traps similar to those described by Tebbens and Drinker,7 placed in a liquid nitrogen bath. These traps remove higher oxides of nitrogen and leave only nitric oxide. Low temperature vapor pressure properties of the oxides, indicated in table 2, show that at least 77.S p. p. m. of NO can escape this trap, whereas all others should be retained. Gases were drawn through the traps continuously at a rate of 1 L. per minute. It was necessary between samples to warm the traps to allow condensed oxygen and carbon dioxide to volatilize. By this means it was possible to determine NO in addition to NO2 and total oxides. In run 6 two grab samples were collected after the freezing trap, one of which was analyzed for NO as total oxides; the other was analyzed for NO as NO2. This gave an indication of the rate at which NO is oxidized to N02 in the short period of passing into the flask containing an absorbing reagent. . The analytic method employed for nitrogen dioxide was that using /3-naphthylamine 6-8 disulfonic acid reagent with-the a-naphthylamine method as outlined in Snell and Snell.8 This method detects nitrogen dioxide (NO2), nitrogen trioxide (N2O3) and nitrogen tetroxide (N.O.). Harrold and associates 9 indicated the desirability of using this method. We found it was necessary to prepare fresh standards daily to get uniform and accurate results. Table 2.--Low Temperature Properties of Oxides of Nitrogen* Gas NO NOa N2O5 N2O3 N2O Temperature Range, C. -- 200 to --161 solid --100 to -- 40 solid -- 30 to + 30 solid -- 25 to 0 liquid --144 to -- 90 solid * Based on International Critical Table data, t Temperature of liquid nitrogen bath. Vapor Pressure at --196 0.,t Mm.Hg. 0.059 1 x 10-2* 1 x 10-86 3.98 X 10-" 1.2 X 10- Gas Escaping Trap at Atmospheric Pressure, P.p.M. 77.5 0.000 0.000 0.000 0.001 For total nitrates, the United States Bureau of Mines' method 10 using phenoldisulfonic acid was employed. All samples were analyzed on a photoelectric colorimeter (Klett or Coleman). Although it has been indicated that nitrous oxide may be present, it is very difficult to determine this gas, since there are no direct procedures. The methods available are too compli cated to use in a situation such as resulted in this experiment, and therefore attempts to determine N2O directly were unsuccessful. Attempts to oxidize N2O to total nitrates or to reduce it to ammonia failed, since only 3 per cent conversion was attained in one case and less than 1 per cent in the other. This is in agreement with other studies which indicate the chemical stability 6. Silverman, L., and Ege, J. F., Jr.: A Welding Fume Sampler, J. Indust. Hyg. & Toxicol. 26:316, 1944. 7. Tebbens, B. D., and Drinker, P.: Ventilation in Arc Welding with Coated Electrodes, J. Indust. Hyg. & Toxicol. 23:322, 1941. 8. Snell, F. D., and Snell, -C. _T.: Colorimetric Methods of Analysis, Including Some Turbidimetric and Nephelometric Methods, ed. 2, New York, D. Van Nostrand Company, Inc., 1936, vol. 1. 9. Harrold, G. C.; Meek, S. F., and McCord, C. P.: A Chemical and Physiological Investi gation of Electric Arc Welding, J. Indust. Hyg. & Toxicol. 22:347, 1940. I 10. Beatty, R. L.; Berger, L. B., and Schrenk, H. H.: Determination of the Oxides of Nitrogen by the Phenoldisulfonic Acid Method, R. I. 3687, United States Department of the Interior, Bureau of Mines, February, 1943. ..