INDUSTRIAL A S D ENGINEERING CHEMISTRY
390
the catalyst (SnS), which was added. The amount of sulfide sulfur increases with the time of hydrogenation, while the pyritic and organic decrease. The pyritic sulfur may be high, because it is determined directly from the nitric acid extraction and may contain some of the organic sulfur. Residue 1 (least hydrogenated) has a much higher total sulfur content than residues 2,3, and 4,which have almost the same amount of sulfur; yet residue 4 (13.8 grams) has about the same amount (0.88 gram) as residue 2 (26.8 grams) which has 0.86 gram. The sulfate sulfur is shown to be erratic by the data in Tables? and 11. Since residue 4 had been standing in the laboratory considerably longer than the others and had a higher percentage of sulfate sulfur, it was suspected of having gained a t the expense of the sulfide sulfur. The writers wish to thank C. H. Fisher and Abner Eisner of
VOL. 10, NO. 7
the Organic Laboratory for providing the insoluble residues for this work. Literature Cited (1) Am. SOC.Testing Materials, “Standards on Coal and Coke,” p. 21, 1936. (2) Fisher, C. H., and Eisner, Abner, IND.ENG.CHEM., 29, 1371-6 (1937) (3) Fuel Economist, 13, 495-7 (1937). (4) Griffin, R. C., “Technical Methods of Analysis,” 2nd ed., p. 142, New York, McGraw-Hill Book Co., 1927. (5) Powell, A. R., Bur. Mines Tech. Paper 254 (1921). (6) Powell, A. R., IND.ENG.CHEM., 15, 951-3 (1923). (7) Powell, A. R., and Parr, S. W., Expt. Sta., Univ. Illinois, Bull. 111, 10-35 (1919).
RECEIVED May 3, 1938. Presented before the Division of Gas and Fuel Chemistry a t the 95th Meeting of the American Chemical Society, Dallaa, Text%, April 18 to 22, 1938. Published b y permission of the Director, Bureau of Mines. United States Department of the Interior. (Not subject to copyright.)
Determination of Small Quantities of Methvl Bromide in Air J RUTH L. RUSBEY AND NATHAN L. DRAKE Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, College Park, RId.
A method is proposed for the determination of methyl bromide in air of fumigated spaces. The procedure involves saponification of the methyl bromide by alcoholic potassium hydroxide, removal of the alcohol, oxidation of the bromide to bromate by sodium hypochlorite, and iodometric titration of the bromate. Results are reported of analyses of 13 samples ranging from 0.0480 to 0.0065 gram. The average error is -1.7 per cent; the greatest error is -3.5 per cent.
T
HE discovery that methyl bromide is an effective fun& gant for a number of insects and is a t the same time
relatively innocuous to plant tissues has resulted in a good deal of experimental work with this compound by entomologists. Consequently, the need has arisen for a method of determining methyl bromide in the air of fumigated spaces, and it is the purpose of this paper to present such a method. There is little information in the literature bearing directly on the determination of methyl bromide. Kuckolls (5) determined the concentration of alkyl halides, including methyl bromide, in air by condensation with liquid air and subsequent pressure measurements a t the original temperature. Glaser (2) reported determining the methyl bromide content of air in a refrigerator factory by drawing 100 liters of air through sodium methylate solution, then acidifying and titrating with 0.01 X silver nitrate and ammonium thiocyanate. The Dow Chemical Company (1) has proposed a method which involves saponification of the methyl bromide with alcoholic potassium hydroxide solution and subsequent titration with standard silver nitrate solution, using dichlorofluorescein as an adsorption indicator
h number of samples of methyl bromide were analyzed in this laboratory by the Dow method, but with small samples the end point was very unsatisfactory. The procedure to be described is more time-consuming, but the end point is much sharper and easier to detect. Oxidation of the bromide to bromate also introduces a sixfold magnification in the results, which further contributes t o the accuracy. After saponification with alcoholic potassium hydroxide, the bromine of methyl bromide is in the form of potassium bromide. The alcohol can be removed readily and an aqueous solution obtained which contains potassium bromide and excess potassium hydroxide. Leipert and Watzlawek (3) have described a method, based on earlier work by van der hleulen ( d ) , for the microanalytical determination of bromine in organic substances which consists essentially in combustion of the substance in oxygen, absorption of the combustion products in aqueous sodium hydroxide solution, and subsequent oxidation of the bromine to bromate. The oxidation and titration processes were easily adapted to a larger scale for the present purpose. The method of analysis to be described involves passing air containing methyl bromide through heated alcoholic potassium hydroxide solution to produce saponification. The mixture is diluted with water and the alcohol removed by distillation. The bromide is then oxidized to bromate by sodium hypochlorite in slightly acid solution, the excess hypochlorite removed, potassium iodide added, and the iodine titrated with standard sodium thiosulfate solution. Apparatus A special saponification apparatus is required, which is shown in Figure 1. (This is a slight modification of an apparatus described in a private communication from the Dow Chemical Company.) The glass tubing is 6 mm. in diameter except for portion EE, which is capillary tubing of about 1-mm. diameter. The bulbs are 3 cm. in diameter except for the three at the bottom, whose diameter is 2.5 cm. A tin can of suitable dimensions, covered with thin asbestos, is used for the jacket, D, which is held in place by a rubber stopper at F. A piece of cardboard is used
JULY 15, 1938
391
AXAL'k-TICAL EDITIOM
to extend the jacket above the side arm. There is a 10/30 female standard taper connection at -4for attaching the sampling bulbs. Air-sampling bulbs were made from pieces of P rex tubing 7 cm. in diameter and 50 em. long, d r a m down on t l e ends and sealed to stopcocks ground for high vacuum. A 10/30 male standard taper connection was sealed on at one end. These bulbs, which had a capacity of approximately 2 liters, were highly evacuated and tested for leaks over a period of several days. Samples were taken by evacuating a bulb and then opening one of the stopcock. to the fumigated air.
0.1 Ar or 0.05 K,depending upon the size of the methyl bromide sample. Starch indicator solution. 2 N hydrochloric acid. Methyl bromide obtained by fractional distillation of t,he commercial product. After considerable low-boiling material, probably wet, had been collected, the fraction boiling at 3.4' to 3.6" C. was retained for use. Samples of this were sealed and weighed in the glass capsules previously mentioned.
Experimental Procedure Twenty-five milliliters of the alcoholic potassium hydroxide solution and 10 ml. of ether were introduced into the saponification apparatus through stopcock G. This stopcock was then closed, but the one at A was left open. Jacket D was filled with small lumps of solid carbon dioxide and was kept filled throughout the saponification. One of the sample capsules was placed in the sample adapter of Figure 2 and held in place by the glass rod. The sample adapter was then connected to the saponification apparatus. A compressed-air line was attached to stopcock L, and air was passed through the apparatus at the rate of 3 bubbles per second. The three bulbs a t the bottom of the saponification apparatus were immersed in a water bath so t h a t water covered the bulbs but did not reach capillary tube E. The bath was kept at 68" C., a temperature that caused the ether t o siphon down through the capillary tube about once every minute or two but did not cause any loss of ether vapor a t C. While the water bath was heating, solid carbon dioxide was packed around the portion of the sample adapter where the sample lay and was kept there for a t least 10 minutes. The sample was thus cooled so that it would not evaporate instantaneously when the capsule was broken. When the ether was siphoning regularly and the sample was well chilled, the capcule was broken by glass rod M and the solid carbon dioxide was removed from around the sample. The rate of evaporation of methyl bromide was controlled, when necessary, by the application of solid carbon dioxide, so that about 20 minutes were required for complete evaporation. The stream of air was then continued for one hour. The stopcock a t A was then closed and the apparatus taken down. After the solid carbon dioxide had been removed from the jacket, the saponification apparatus was rinsed thoroughly with distilled water. The combined washings were put in a 500-ml. round-bottomed flask, distilled water was added to make the volume about 250 ml., and distillate was removed until it gave no more than an extremely faint iodoform test,. Water was added occasionally so that the final volume was about 150 ml. Removal of the alcohol is necessary to avoid reduction of the sodium hypochlorite that is added later.
5s-
50--
45.-
40--
35.-
l
i E 30--
w b
-
--
f
25-
u
-
20.-
Is--
io--
5-
0-
b
5
10 15 CCNTIMETCRS
FIQURE 1. SAPONIFICATIOS
20
4
25
APPARATUS
The device shown in Figure 2 was made for the introduction of weighed samples of methyl bromide into the saponification apparatus. It was fabricated mainly from a 24/40 standard taper ground-glass joint, K , K'; a 10j30 connection at H fits the saponification apparatus, and an indentation a t I holds the sample capsule in place. M is a glass rod which slides through the rubber slip joint, N . The rod is flattened and slightly indented on the inner end. Small glass capsules to contain samples were made of the shape shown in 0 of Figure 2.
Reagents Ethyl alcoholic solution of 20 grams of reagent-quality potassium hydroxide per liter. Diethyl ether. Solid carbon dioxide. Solution of sodium hypochlorite made by absorbing 7 grams of chlorine in 100 ml. of 12 per cent aqueous solution of reagentquality sodium hydroxide. Reagent-quality sodium chloride. Reagent-quality boric acid. A 10 per cent aqueous solution of reagent-quality sodium formate. Reagent-quality potassium iodide. A 5 per cent aqueous solution of ammonium molybdate. A standardized solution of sodium thiosulfate, approximately
I H
n
/
u \
v
o A
I
FIGURE 2. SAMPLE ADAPTER The flask containing the residual liquid was placed in a boilingwater bath, and to it were added 20 ml. of sodium hypochlorite solution, 5 grams of sodium chloride, and 10 grams of boric acid. Heating in the water bath was continued for 15 minutes, whereupon 20 ml. of sodium formate solution were added to destroy the excess hypochlorous acid. The contents of the flask were next boiled for 5 minutes, and cooled, and potassium iodide crystals, a few drops of ammonium molybdate solution, and 50 ml. of 2 N hydrochloric acid were added. The iodine liberated was titrated with standard sodium thiosulfate solution, starch being used as indicator. One milliliter of 0.1 N sodium thiosulfate is equivalent to 0.00158 gram of methyl bromide. It has been determined that 2-liter air-sampling bulbs can be completely flushed out in 2 hours by a current of air flowing at the rate of 100 ml. er minute. This fact was established by placing a 2-liter bulb !et ween the saponification apparatus and the sample adapter.
*
1NDUSTRIAL AXD ENGINEERING CHEMISTRY
392
OF METHYL BROMIDE DETERMINATIONS BY TABLE I. ACCURACY
THE
MeBr Used Gram 0.0480 0.0355a 0.0333 0.0312 0,0299 0.02930 0.0288@ 0,0278 0,0244
0.0145 0,0125 0.0079
0.0065
METHOD DESCRIBED
Normality
of NaiSiOs
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.05 0.1 0.05 0.05
MeBr Found Gram 0.0474 0.0352 0.0326 0.0304 0.0294 0,0286
0,0279 0.0271 0.0238 0,0140
0.0126 0.0077 0.0066
Error
%
-1.2
-0.8 -2.1 -2.6 -1.7
-2.4 -3.1 -2 5 -2.5 -3.5 +0.8 -2..5
+l.5
Av. -1.; 0 R u n a i t h 2-liter sampling bulb between sample and saponification apparatus.
The results are given in Table I. The average error of 13 analyses is -1.7 per cent; the greatest individual error is
VOL. 10, N O . 7
-3.5 per cent. Samples ranged from 0.0480 to 0.0065 gram. The reproducibility and accuracy of these results are probably much greater than the reproducibility of fumigating conditions. The quantity of methyl bromide used in fumigating is usually about 2 pounds for each 1000 cubic feet of space, which is equivalent to approximately 0.064 gram in a 2-liter sample of air. Consequently the range of samples analyzed probably coincides roughly with that encountered in actual practice. The use of more dilute thiosulfate would permit the determination of smaller samples.
Literature Cited (1) Don- Chemical Co., private communication. (2) Glaser, Deut. 2. ges. gerichtl. MecZ., 12,470-4 (1928). (3) Leipert and Watslawek, 2. anal. Chem., 38,113-16 (1934).
(4) Meulen, ran der, Chem. Weekblad, 28, 82 (1931). (5) Nuckolls, Underwriters' Laboratories' Rept., Mise. Hazard No. 2375 (November 13, 1933). RECEIVED May 6, 1938.
A Modification of the Markley Melting Point Apparatus MILTON S. SCHECHTER AND H. L. HALLER Bureau of Entomology and Plant Quarantine, U. S. Department of .4griculture, Washington, D. C.
T
HE Markley melting point apparatus (1) has been used
satisfactorily for some time in this laboratory. The apparatus is essentially a large Thiele tube in which very rapid circulation of liquid is obtained through the use of an efficient stirrer, ensuring rapid interchange of heat between
the liquid, the melting point tube, and the thermometer. However, the usual methods of attaching the melting point tube to the thermometer have proved very troublesome. The use of a small rubber band or a small spring requires the removal of the thermometer from the bath, the attachment of the melting point tube, and the replacement of the thermometer in the bath each time that a reading is to be taken. Furthermore, there is always the danger of breaking the thermometer . The apparatus was therefore modified by sealing to it two side arms of 3-mm. tubing in such a position and a t such an angle that, when melting point tubes are inserted, their lower ends come in contact with the thermometer bulb. The side tubes should be long enough so that their open ends will come above the highest level to which the liquid in the apparatus will rise during its operation. It is advantageous to have the angle between the side tubes and the vertical as small as possible, about 35 degrees. Each side arm is wound with a short piece of wire (such as No. 25 chrome1 A), the end of which is bent over the opening in such a manner as to press the melting point tube against the inner surface of the side-arm tube. The melting point tube will thus be held steady and the lower end will be pressed in contact with the front of the thermometer bulb. This modification of the apparatus simplifies the determination of melting points, since the melting point tubes can readily be inserted or withdrawn through the side arms. The thermometer may be left permanently in place by inserting it through a cork having a 90-degree sector cut out so that the cork Kill not block part of the thermometer scale. A commercial grade of chlorinated diphenyl, as recommended by Dr. Markley in a private communication, has been found to be a satisfactory substitute for the usual sulfuric acid-potassium sulfate mixture.
Literature Cited (1) Markley, K S., IND. ENG CHEX, Anal Ed., 6, 475 (1934). FRONT VIEW
SIDE V I E W
RECEIVED .\pril 26. 1938.
