DISCUSSION AND CONCLUSIONS
From t l i r data of Figures I , 2, and 4, it appears that hydrolysis of the complex occurs rapidly in alcoholic solution at, room temperature. A decrease from 430 to 165 takes place over a 06hour pcriod at the 2-p.p.m. boron concentration, whereas no difference was observed in readings taken betwecn 16 minutcs and 2 hours. The rate of decrense is the same a t all concentrations used, as shown by straightline ciirveq in Figurr 1 and the slopes of the ciirvcs for thc room tcmpcrature readings plottcd on semilog paper for 0.2-, 1.0-, and 2.0-p.p.m. boron concentrations. That thc hydrolysis is affccteri by tcmpcraturc is wcn hy the
ncgligiblc decrease in color of samples stored at 0" C. (Figure 2). Dry storage of the boron-curcumin complex showed the noimal hydrolysis of the complex at room temperature following addition of alcohol to the samples, provided samples were not stored longer than 24 hours. If the samples were stored dry for 1 to 4 weeks, the normal hydrolysis was replaced by a 2-hour lag in maximal color development. The development of a lag pcriod for the 2-p.p.m. sample at 2week dry storage resultfd in a decrease in wading from 440 to 270, with full rccovery a t 2 hours. Alcohol addition to dry storage mmplcs a t 0, 1, 2 , or 3 days (Figure 4) resulted in thc same amount of hydrol-
ysis regardless of the length of time of storage. Again samples, stored in alcohol R t 0" C. showed only a small decrease in color reading up to 5 days as compared to the rapid decrease a t room temperature. The curcumin-oxalic acid reagent is stable when refrigerated. A reagent sample stored for 1 ycar a t 0" C. gave readings when used in boron detcrmination identical with those obtained the previous year with the same reagent. LITERATURE CITED
(I) Dible, W. T., Truog, E., Berger, I
C O R R E C T I O N S FOR P R E P b R l N G NITROGEN O l O X l D E GAS M I X T U R E S
0
Figure 5. mixtures
200 400 SO0 NITROGEN OlOXlOE PbRTIPL PRESSURE.
mm. H g
aoo
Corrections for preparing nitrogen dioxide gas
pressure), Thus the tank gage pressure is very sensitive to temperature. On a cold day i t is possible for air to enter the tank when the valve is opened. Cooling due to evaporation of the liquid nitrogen dioxide in the tank or throttling in the needle valve was also troublesome. The pure gas is too corrosive for any connections other than glass. Much steadier operation waa obtained by metering a tank mixture (0.5% nitrogen dioxide in air or nitrogen is recommended), Ordinary rotameters were used for flow measurements. Motor-driven glass syringes were also successful for metering lower concentrations of mixtures. The tank gas mixture was analyzed gravimetrically by passing it through two absorbing U-tubes in series and then through a wet-test meter to measure the volume of unabsorbed gas. Temperature and barometric pressure readings were made. Two thirds of each tube was filled with Ascarite and the remaining third, on the outlet end, with Anhydrone. Both tubes were weighed on an analytical balance before and after the run. The gain in weight of the first tube represented the absorbed nitrogen dioxide, while the unchanged weight of the second tube demonstrated the high absorption efficiency of the first. The tank mixtures were reasonably assumed to contain negligible amounts of water vapor. Serious discrepancies between the analyzed and nominal values of tank mixtures indicated that the supplier had neglected the large deviations of nitrogen dioxide from the ideal gas laws. This occurs because nitrogen dioxide partially dimerizes in reversible equilibrium affected by both the temperature and the partial pressure of nitrogen dioxide. The extent of this effect is shown in Figure 5 computed from available data (19).
Thus if I-atm. pressure of nitrogen dioxide is introduced into an evacuated tank and the latter is then pressurized to 100 atm. with air or nitrogen, the actual concentration is 1.7%, although the nominal concentration is 1%. Analytical results for some tanks were so high that they indicated the probable presence of liquid nitrogen dioxide. When the gas was introduced into these tanks, apparently atmospheric pressure was exceeded or the tank wm below the condensing temperature. The percentage composition of a gaa mixture in such a tank is variable and, in this case, it is calculated as the vapor pressure of nitrogen dioxide (corrected to ideal conditions) a t the tank temp6rature divided by the total pressure of the gas in the tank. Such a calculation is complicated, because the high tank pressure affects the vapor pressure of liquid nitrogen dioxide appreciably. By specifying a tank mixture in which the partial pressure of nitrogen dioxide is considerably below 1 atm. during the filling operation, this error may be avoided. Low concentrations of nitrogen dioxide in air may be determined using Griess-Saltzman reagent (14). Levels above 1 p.p.m, may be sampled in evacuated bottles containing 10 ml. of the reagent, lower levels by using a midget fritted bubbler (maximum pore diameter of 60 microns) a t a flow rate of 0.4 liter per minute, A direct redviolet color appears and may be r e d spectrophotometrically a t 550 rnk after allowing 15 minutes for full color development. The standardization with sodium nitrite is empirical, a8 described in the original paper (14). Phosgene. Phosgene mixtures were prepared by a double dilution system, The pure gas, from a cylinder containing the liquid, was metered with an asbestos plug flowmeter. The test data suggested that although the purity
of thc gas was listcd by the manufacturer as 99.0% minimum, an inert gas was actually present in the tank. This may have been carbon monoxide resulting from partial decomposition of the phosgene. Although the initial purity of the gas issuing from the tank was less than 50%, this value rose rapidly to 100% after the tank had been used for a moderatc time. Thus the impurity appeared to be flushed out readily. Since no proved methods of chemical analysis wcre available for low concentrations of phosgene, intermediate concentrations were sampled from the first dilution gas stream. The iodometric method of Matuszak (10) was applied successfully. The sample air stream is bubbled through 2% sodium iodide solution in anhydrous acetone, and a molecule of phosgene reacts to liberate a molecule of carbon monoxide and two iodine atbms. Matuszak employed a ritandard thiosulfate solution and starch indicator for titration of the liberated iodine. However, he recornmended certain extra steps prior to the final titration to prevent errors caused by side reactions, Thus in the presence of moisture less iodine may be liberated because of the
