A N A L Y T I C A L EDITION Vol. 6, No. 5 gas is then admitted until the manometer remains constant at TABLEI. VACUUMDISTILLATION AT 40 MM. PRESSW~ the working pressure, generally 8 to 20 mm. of mercur dependORIQINAL TOPPEID ing upon the extent of to ping desired. This gas suppr; is easily CRUDJJ CRUDJJ~ Initial temp., C. 114 194 controlled by a fine neeie valve which has a constant pressure 1.35 0.0 of one ound r square inch (0.07 kg. per sq. cm.) gage on the 8.80 0.0 inlet d e , so t%t in effect the needle valve acts as a flowmeter, 15.70 0.0 and, once the initial evacuation ressure and working pressure 28.20 1.2 35.75 11.5 have been fixed, there will be no gctuation unless leaks develop. 43.55 21.0 There will be small amounts of dissolved gas evolved from the a Topped at 158; C. (boiling turpentine) and 19 mm. total pressure with crude, but, if the pump has ample capacity and the crude input about 18 mm. partial Dressure of natural 888. to the degasser is kept reasonably constant, these gases will not A four-unit apparatus has also been constructed, in which the units are connected in parallel to the crude-oil source, topped-oil receiver, gas inlet, distillate receiver, and vacuum pump. Topped oil from this apparatus, using nitrogen as the inert gas and a temperature of 158’ C., shows virtually the same characteristics as that given in Table I. There is a small gap between the topped oil and the distillate, as shown in Figure 2, where distillation curves for the crude oil, topped oil, and distillate are given. These are all made with a standard Engler apparatus. The curves indicate that the separation is fairly sharp. The apparatus described is very flexible from an operating standpoint. Liquids covering a wide range of boiling points may be used as the heating medium, and pressures may be VOLUME DISTILLED, PER CENT varied over a considerable latitude. The partial pressures FIGURE2. ENGLER DISTILLATION CURVES of the gas used may also be changed to suit conditions, as may the kind of gas used. It is obvious that the capacity of such appreciably affect the pressure. A flowmeter couldibe inserted advantageously in the gas supply line t o afford visual evidence an apparatus is small. The four-unit set-up has a capacity of the amount of gas entering. After a constant working pres- of 200 to 300 grams of topped oil per hour when used with sure has been set, the crude is allowed to enter slowly until tem- the crude oil mentioned above under conditions removing perature equilibrium in the fractionating tower is attained, when about 21 per cent of the crude. The apparatus may be conthe rate of crude input is fixed t o maintain the desired temperature at the top of the fractionator, as indicated by the copper- structed readily from materials usually available in the laboraconstantan thermocouple, W. If the entire ap aratus is well tory. insulated, uniformly reproducible results shoufd be possible LITERATURE CITED since the following factors, which also control the reflux, are fixed: total and partial pressure, heat input, and crude input. (1) Smith, H. M., Bureau of Mines, Tech. Paper 428 (1928). (2) Smith, H. M., et al., Ibid., 477 (1930). This apparatus has been used for topping a crude oil from RJJCJJIV~D May 25,1934. Presented before the Division of Petroleum Chemthe Port Neches Field, Texas. The characteristics of the iatry at the 12th Midwest Regional Meeting of the American Chemical original crude and of the topped oil, as indicated by vacuum Society, Kansaa City, Mo., May 3 to 8 , 1934. Published by permission of distillation at 40 mm. pressure, are shown in Table I. S. Bureau of Mines. (Not subject to copyright.) 374
Determination of Phosgene by the Soda Method I
Effect of Fire-Extinguisher Chlorinated Hydrocarbons MARYAN P. MATUSZAK,~ U.S. Bureau of Mines, Pittsburgh, Pa.
I
T HAS been claimed (6) that values obtained by the U. S. Bureau of Mines with the alcoholic soda method (2,S),for phosgene produced by oxidation of carbon tetra-
chloride, were too high because of “hydrolysis of carbon tetrachloride and other chlbrinated hydrocarbons.” That no error due to the presence of carbon tetrachloride was found in blank determinations made under the specified conditions of analysis was confirmed by a tube experiment (2, Table 111), in which three determinations showed no phosgene whatever, although a concentration of carbon tetrachloride of 14,000 p. p. m. was present. In several similar blank determinations the writer has likewise failed t o detect any error due to absorption and saponification of carbon tetrachloride, even when using a more sensitive technic (4) in the Mohr titration than the earlier workers. It is not implied that carbon tetrachloride cannot be Present address, 301 South Creek Ave., Bartlesville, Okla.
saponified by alcoholic soda. But if the conditions of analysis used in the earlier work-absorption, a t 0.5 liter per minute, of 4 or 5 liters of air Containing carbon tetrachloride up to 5850 p.p.m., or of 0.5 to 1 liter containing up to 14,700 p. p. m., by a petticoat-bubbler ahsorber containing 50 cc. of N sodium hydroxide in 85 per cent alcohol-are maintained, and if neutralization is not unreasonably delayed, no error due to this compound is present. Chloroform, the next most abundant component of commercial fire-extinguisher liquids, saponifies more readily than carbon tetrachloride (6). Hence, experiments were made to determine the concentration a t which it causes a detectable error under the conditions of analysis. Chloroform-containing air samples, 5.08 liters in volume, were absorbed by 50 cc. of N sodium hydroxide in 85 per cent alcohol in a petticoat-bubbler absorber during 10.5 minutes. The Mohr determinations were made with great care. Neutrali-
September 15,1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
zation was made to phenol hthalein with nitric acid, concentrated at first and 0.25 N near t t e end. Althou h no effort was made to hurry the work, neutralization was usua!ly made within about 10 minutes after absorption. Heat liberated during neutralization was removed by cooling with tap water, to avoid decreasing the sensitivity of the chromate indicator. Then 1 cc. of M sodium bicarbonate was added, t o insure a pH of about 9, and 1 cc. of 10 per cent potassium chromate. Comparison of the titrated solution was made by reflected (not transmitted) yellowish light against a gray background with a freshly prepared reference solution containing similar amounts of reagents and a slight excess of sodium chloride. Some flasks of Pyrex glass made the yellow solution appear darker than others, an effect that appeared to be independent of wall-thickness; hence, the flasks used were matched to eliminate this effect. Titrations were continued until the reddish end point persisted for at least 5 minutes. This sometimes took 15 minutes or more, for although an apparently permanent end point was reached with the first 2 or 3 drops of 0.00818N silver nitrate, a much larger volume could be added after several minutes. The data are given in Table I.
375
hydroxide absorbs phosgene very effectively and is more stable and absorbs less chlorinated hydrocarbons. The method of purification of fire-gases with zinc and mercuric sulfide (1) is preferable to the original method of purifying with silver nitrate and antimony trisulfide ( 2 ) . The principal objection to the older method-that nitric acid, formed in the removal of hydrogen chloride by silver nitrate, reacts with antimony trisulfide to give hydrogen sulfide-is obviously inoperative if the gas is passed first over antimony trisulfide and then over silver nitrate, for any hydrogen sulfide formed by reaction of the former with hydrogen chloride is removed by the latter. LITERATURE CITED
(1) Anonymous, Jahresber. &em.-techn. Reichsanstalt, 5, 11-20 (1926). (2) Fieldner, Kata, Kinney, and Longfellow, J. Franklin Inst., 190, 543 (1920). (3) Fieldner, Oberfell, Teague, and Lawrence, J. IND.ENQ.Can 11, 523, 527 (1919). TABLEI. ABSORPTIONAND SAPONIFICATION OF CHLOROFORM (4) Kolthoff and Furman, “Volumetric Analysis,” Vol. 2, pp. 211-24, APPARENT APPARENT John Wiley & Sons, N. Y., 1929. CELoR oFoR M PHOBG~NE CHLOROFORM PH00081NE (5) Kunke, J . Assoc. Oficial Agr. Chsm., 12, 264-76 (1929); C. A., P.p . m. P.p . m. P.p . m. P.g. m. 23, 4772 (1929). 0 3990 43 1000 (6) Olsen, Ferguson, Sabetta, and Scheflan, IND.ENQ.CHEM.,Anal. 3 6410 59 1410 2 6750 92 1430 Ed., 3, 189-91 (1931). 3 5170 113 1496 153 10920 16 1950 R ~ C E I V EApril D 21, 1934. Published by permission of the Director, U. 8. 44 14S00 196 2510 14600 190 Bureau of Mines. (Not subject to copyright.) 43 2530
Since, in the fire experiments (2, Table 11),the concentration of fire-extinguisher liquids varied from 2000 to 5130 p. p. m. (calculated as carbon tetrachloride) and since only about 10 per cent of this was introduced as chloroform, no error due to absorption and saponification of this compound was present. Such error, even with the more sensitive titration technic, does not begin to appear until the chloroform concentration is a t least twice the maximum introduced in the fire experiments. In the tube experiments (2, Table IV) the initial concentration of chloroform was of the order of 1400 p. p. m. But, even if it all escaped decomposition or oxidation-which could scarcely have been true, as the total concentration of chlorinated hydrocarbons decreased by about 38 per centa detectable error was unlikely, as the air samples and the absorption periods were only one-fifth or one-tenth as large as those used in obtaining the data of Table L Moreover, any possible error must have been negligible in comparison with the phosgene reported, 3700 to 3800 p. p. m. Other experiments showed that Pyrene, a typical fireextinguisher liquid (2, KO. l), was several times more resistant to saponification than chloroform, indicating that the values of 15 to 60 p. p. m. for phosgene found in fire-gases by the Bureau of Mines were not subject to any appreciable error because of chlorinated hydrocarbons introduced as fire-extinguisher liquids. The alleged high soda values obtained by other workers (6) were probably due to insufficient removal of hydrogen chloride or precipitation of silver carbonate in the Mohr titration (4). The former appears to account for the only numerical data published in support of the alleged error, which were obtained with the unpurified gas from a toluene solution of phosgene and not with purified fire-gases; the latter, for the high values obtained in experiments on the thermal decomposition of mixtures containing carbon tetrachloride, for which no numerical data were published. Such error would be the more prominent the larger the air samples taken for analysis. The soda method can be improved by acidifying with nitric acid and boiling out the carbon dioxide before neutralizing and titrating, and can also be rendered less objectionable by eliminating the use of alcohol. Aqueous N sodium
A Distillation Apparatus for Phenols in Water ELDONA. MEANESAND EDWARD L. NEWMAN Wichita Testing Laboratories, Wichita, * Kans.
T
HE apparatus illustrated was designed for the steam distillation of phenols from water solutions, and is simpler and more compact than the usual type. Instead of the box with a series of tubes and connections as described by Shaw (I), the outfit is condensed into a single unit. This consists of a glass tube, A , divided into two compartments B and C. In part B is placed distilled water and in art C is placed the sample to be distilled. ThrougR an inner tube fitting down into the lower compartment a slow stream of washed air is passed. The air becomes saturated with moisture and passing up is deflected down through the sample, releasing its moisture and maintaining a fairly c o n s t a n t volume. The tube is surrounded by a glass jacket. Steam, generated in flask D,passes up around the tube and escapes at the top, maintaining the temperature for distillation of the sample. The phenols present are thus distilled over and are condensed and collected in a graduated cylinder. Connections with which the vapors come in contact are made by means of ground-glass stoppers. No rubber tubes or stoppers are used, thus eliminating any possible contamination.
/
Any suitabIe indicator may be used to ascertain the amount of phenol in the distillate. LITERATURE CITED (1) Shaw, J. A,, IND.EKG.CHEM.,Anal. Ed., 1, 118 (1929). RBCEIYED July 11, 1934.
