538
Vol. 16, No. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
A Modification
of the Ethanolamine Hydrolysis Method for Determination of Methyl Bromide ROBERT D. CHISHOLM AND LOUIS KOBLITSKY
United States Department of Agriculture, Bureau of Entomology and Plant Quarantine, Moorestown,
T
H E study of the insecticidal value of methyl bromide as a fumigant requires a method for determination of this compound mixed with air. A modification of the method described by Stenger et al. (I) has been developed for its determination in the atmosphere of chambers during fumigations. The sampling methods described by Stenger et al. (I) for various reasons could not be applied directly under some of the conditions which the authors encountered in their work, which required taking successive samples from several locations simultaneously. The modification developed involves withdrawal by aspiration of a portion of the atmosphere of the chamber, passing it through a series of absorption tubes packed with sand wet with ethanolamine, and subsequent determination of the bromide ion by the Volhard method. In this way gas losses during sampling are avoided. Various types of absorption tubes may be used. The one which the authors found most satisfactory was made from 1-cm. (inside diameter) glass tubing bent in the form of a V, with the bend flattened so that the packing could be retained in one arm. The sand used for packing was of such a size t h a t it would pass through a 10-mesh screen but be retained on a 16-mesh screen. It was prepared for use by digesting with concentrated nitric acid, washing free of acid, and igniting. The absorption tubes, each containin a column of sand 25 cm. high, moistened with 2 ml. of ethansamine, were connected by means of inverted Utubes, and all joints were rubber-covered glass to glass. The number of absorption tubes in series is dependent upon the concentration of methyl bromide and the rate of aspiration. The authors used four. absorption tubes and a sampling period of 20 minutes. A 2-liter sample was taken for a concentration of 453.6 grams per 28,320 liters (1 pound per 1000 cubic feet) and a 1-liter sample for concentrations of 0.9 and 1.8 kg. (2 and 4 pounds). Usually more than 70% of the methyl bromide was
A
Simplified Fritted-Glass Bubbler RICHARD KIESELBACH Bakelite Corporation, Bound Brook,
N. J.
I
N T H E course of work involving the absorption of gases, a need was felt for a fritted-glass bubbler having the following advantages not to be found in the conventional jar type of bubbler. There should be no dead spaces in the bubbler, so that a minimum of absorbing solution could be used effectively. A minimum of wash water should be required to wash out the solution a t the end of a run. The possibility of loss of liquid while draining and washing should be reduced to a minimum. It should be possible to connect a series of bubblers quickly and easily, without the use of rubber tubing, and without difficulties of alignment. The bubbler should preferably be compact, rugged, and inexpensive. The bubbler shown in the illustration proved to be the answer to the problem, and is of the simplest possible design. When a gas flow rate of 300 ml. per minute is used, the bubbler operates aficiently with as little as 15 ml. of absorbing solution. For special applications, the dimensions could, of course, be altered. I n operation, a series of bubblers is set up in the following manner: The No. 1 bubbler is inserted in the standard taper neck of a flask bearing a tubulature for the entrance of the gas. A slight
N. 1.
recovered from the first absorber, about 20% from the second, 6% from the third, and 2 % from the fourth. Following sampling, the contents of the absorption tubes were washed into Erlenmeyer flasks, and the bromide ion was determined by the Volhard method. Since ethanolamine retards the end point, a blank on the same amount of ethanolamine should be carried through the procedure and allowed for in calculating the results. This method has given results reproducible with a standard deviation of +0.01 pound with methyl bromide concentrations of approximately 1 pound per 1000 cubic feet. The amounts of methyl bromide recovered from a fumigation chamber of 1000 cubic feet capacity ranged from the equivalent of 96 to 1007, of a 1-pound charge (mean recovery 9793, 95 to 100% of a 2-pound charge (mean recovery 97%,), and 91 to 98% of a 4-pound charge (mean recovery 95%). The samples were taken 15 minutes after introduction of the fumigant. However, thir chamber was exposed to the effect of wind. A statibtical analysis was made, u i n g the results obtained from 88 individual samples, to calculate the normal rate of leakage and the increased rate due to wind of different velocities. Using the calculated conrentrations in the chamber a t the time of sampling and comparing with the analytical results, the recoveries were between 1 and 2% greater than those presented. ACKNOWLEDGMENT
The authors are indebted to W. E. Fleming for the statistical analysis of certan of the data. LITERATURE CITED (1) Stenger, V. A., Shrader, S. A.,
CHEM., ANAL.ED., 11, 121
and Beshgetoor, A. W., IND.ENG. (1939).
pressure (lung power is enough, where permissible) is applied a t the tubulature, and the absorbing solution poured into the bubbler. The tubulature is closed by means of a stopcock or pinchclamp to maintain the pressure, and a second bubbler inserted in the neck of the first. The process is repeated for rls many bubblers as are required, and the apparatus is ready for use. Atthecompletionof a run, a suction is applied a t the tubulature of the flask, pulling the solution into the flak. A verv small amount of water from a wash bottle is required to wash down the bubblers, this being sucked down in the same way. Obviously, loss T 24/40 of liquid is next to impossible a t this stage. Ideally, the receiving flask should be so designed that it can be used as a vessel for subsequent reactions.
I
This type of bubbler has on e d i s a d v a n t a g e -t he necessity of maintaining a gas pressure while filling, and until putting into operation--which may preclude its use in certain appiications. For many purposes, however, this inconvenience is more than compensated for by thr advantages listed above.
