I S D r S T R I A L A S D E S G I S E E R I S G CHE;WISTRY
January 15, 1930
107
Apparatus for Destructive Oxidation of Organic Ma= terial in the Determination of Metals in Foods’ J. W. Barnes I\SECTICIDE
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B L R E A LOF
CHE\lISTRY A \ D
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HE apparatus described in this article consists of
ordinary laboratory equipment, slightly modified for use in the total oxidation of organic material. The complete oxidation of organic material in the determination of metals in foods. or in similar processes, calls for the addition of reagents under optimum conditions and the disposal of the irritating fumes of the oxides of nitrogen and sulfur. This apparatus was used in the determination of arsenic in fruit and vegetables ( I , 2, 3 ) . The present article is devoted exclusively to a description of this apparatus because of its much wider application. It has been found convenient and efficient in this laboratory.
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will produce less spattering. The glass in the funnel should be as resistant as that in the flask itself. The wash bottle is of the regulation all-glass type but with the following modifications: I n the stopper is a vent which may be closed m-ith the thumb. This makes it possible to attach the bottle to a source of air pressure and temporarily to close the vent when it is desired to deliver the acid. The delivery tube has a Bunsen valve near the bottom. as shown. The outside arm of this tube is considerably more than the usual length; in this particular case i t is 60 cm. long. This combination of apparatus permits the use of a number of flasks a t one time on a hot plate, and the long arm of the wash bottle a l l o w convenient delivery of portions of acid to each flask. This equipment is decidedly more convenient for the operator than casseroles. pipets, and watch glasses, the equipment sometiiiies recommended. Elaborate Equipment
The apparatus shown in Figures 2 rind 3, a more elaborate set-up for a laboratory hood of moderate size, is an adaptation of’ a Kjeldahl nitrogen apparatus to the particular conditions of the problem. The essential features of the apparatus art’ as follows: The tube (A) for leading the fumes away must be resistant to nitrogen acids, as well as to sulfuric acid. The one in uqe by the writer is of Pyres, but terra cotta or ;acid-resistant iron might serve as well. It is 10 cm. in diameter and 127 cm. 111 length. If flask. are kept in po\ition, whether actually
Figure 1
TKOgeneral sets of equipment are described. (1) a simple arrangement for use on the hot plate and (2) a more elaborate permanent set-up for a hood. Simple Equipment
The arrangement shown in Figure 1 may be used on an ordinary hot plate in a hood with a good draft. It is suitable for laboratories having only occasional need for such oxidation or for an emergency when the more elaborate equipment is not available. I t is an adaptation of an allglass wash bottle, a n Erlenmeyer flask, and a funnel. The lip of the Erlenmeyer flask is bent upward in three places for the purpose of supporting the funnel a little above the flask so as t o allow the escape of fumes through this space and not through the stem of the funnel. Otherwise, the sudden rush of vapors attendant on addition of fresh acid would blow a portion of the acid back u p the tube of the funnel, resulting in loss of acid as well as in some danger to the manipulator. With sufficient care these supports may be made high enough for this purpose and yet not interfere with a stopper when the flask is to be used for other purposes. The wide-mouth flask is convenient, as many samples t o be analyzed are bulky. The funnel is bent as shown so the acid lvill flow down the side of the flask before reaching the reacting material. This 1
Received October 5 , 1929
Figure 2
in use or not, a better draft is obtained because of-the partial stopping of the holes. The glass cylinder with one bank of burners has been in use in the U.S.Food, Drug, and Insecticide Administration for several years, but the other modifications mentioned here were adapted in this laboratory. A glass tube ( B ) leads from a reservoir of nitric acid, and
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A-YdLI'TICAL EDI TIO-Y
side tubes with stopcocks lead froin this tube to the reaction flasks. Reference is frequently made in the literature to the fact that it is desirable to add the nitric acid slowly. With these tubes the acid may be allowed to drip as s l o ~ d y as desired. Actually, the acid is most efficient v-lien it is added just at the cliarring point of the organic material. T h e most effective of several lubricants tried on the stopcocks was graphite. The reservoir containing nitric acid (C) is placed so that the acid runs by gravity to the stopcocks after the siphoning action has been established. The E reservoir may be an ordinary acid b o t t l e on a ring-stand s u p port. A pos=.ible modification would be a pear-shaped reservoir, suspended from a net, with a glass delivery tube sealed t o t h e & "3 bottom. This m u l d E obviate the annoyance of occasionally having Figure 3-Detail of Figure 2 t o s t a r t t h e siphon again, but would introduce an additional danger of breakage. The acid is delivered to this reservoir by pressure
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from a much larger storage reservoir not shown in the diagram. Kjeldahl flasks ( D ) of 800 cc. capacity, reduced to a convenient length (in t'his case 28 cm.), are used. The lips should not be re-formed, as this causes them to catch on the edge of the holes in the outlet cylinder. By making a slight depression (D,Figure 3) it is possible to insert the mouth of the flask further into the cylinder, thus increasing the efficiency of fume disposal. The gas is delivered froin the intake (E) to horizontal Bunsen burners, bent as indicated. This effects a great saving in the height of the apparatus. The valves of the burners are also out far enough to allow convenient access. Iron support rods ( F , Figure 3) for the glass tube ( B ) , not shown in Figure 2, are used. An asbestos curtain (G, Figure 3) reduces the amount of heat reflected from the upper row of burners against the stopcocks on the acid delivery tube, not shown in Figure 2. This arrangement permits the use of a double tier of apparatus. The lower tier may be devoted t o the actual oxidation, and the upper tier to the final expulsion of nitrogen oxides and the destruction of the nitrosyl-sulfuric acid. The long-neck glass wash bottle described is very convenient for adding water to the flasks in position. The stream should be directed against the wall of the flask rather than directly into the acid. The addition of a small amount of ammonia will aid in completing this reaction. This apparat'us is distinctly more efficient in the disposal of fumes, consumption of reagents, and saying of time than the simple equipment first described. Literature Cited (1) Barnes, IXD.ENG. CXEX., 21, 172 (1929). (2) Barnes and ?rIurray,Ibid.,21, 1140 (19291. (3) Barnes and Murray, I b i d . , Anal. Ed., 2, 29 (1930).
A Convenient Arrangement for a Titration Table' J. W. Stillman and T. L. Bartleson E. I.
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HEN standardized solutions for volumetric analysis are used regularly in considerable amount, it is advisable to make up large quantities a t a time. For convenience the bottle containing the standard solution should be connected to the buret in some form of a closed system. One common method is to place the stock bottle on a shelf above the laboratory table, the buret being filled by gravity flow. This arrangement has several disadvantages, chief of which are that if a leak develops in any part of the line connecting the bottle and the buret the whole solution may run out, and that when several solutions are maintained the row of bottles and connecting tubes makes a clumsy appearance. The accompanying figure shows a convenient arrangement which presents a neat appearance. A is a 20- or 40-liter bottle which is set on the floor below the table. In one hole of the stopper is inserted a soda-lime tube through which air enters as the solution is used. Through a second hole runs a glass tube reaching to the bottom of the bottle and connecting with the three-way stopcock of the buret. The buret is mounted on a special rod, B. This rod is hollow and has two clamps (A. H. Thomas Co., catalog number 3236) welded on in the positions shown in the figure. The rod is 1 Received September 30, 1929. Contribution 21 from the Experimental Station of E I . du Pout de Nemours & Company.
t h r e a d e d for several' inches a t the lower end and by means of two nuts is clamped to the wooden table top, C. The working suiface of the table. D. is of white T'itrolite, and it is not desirable to put any pressure on this material. A t the p o i n t where the rod passes through the table a thin, loose collar, similar to those used in plum bi n g pr a ct i ce where faucets are attached to porcelain, is used. Both ends of the rod are finished for rubber-tube connections. A t the top an i n v e r t e d U - sh a p e d glass tube makes the connection between the
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