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I N D USTRJAL AND ENGIiVEERING CHEiMIXTRY
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point from 80 to 100 per cent, provided, of course, that the normal humidity in the atmosphere does not exceed that required in the cabinet. Suggested Improvements After several months' experience with the apparatus described, the writers would suggest several improvements to increase its adaptability to laboratory use. The bottom of the cabinet could either be built at a slight angle with the horizontal or suitably grooved to permit
Vol. 20, No. 11
draining off into the drip pan of moisture deposited a t very high humidities. The cabinet could be constructed so that the top is inclined a t an angle of 15 to 20 degrees with the horizontal. This would allow moisture deposited a t high humidities to run down to the end instead of dripping on samples. In place of a single water spray nozzle a series of several nozzles would be preferable. The efficiency of water as a source of vapor supply would be very greatly increased if the air were passed through a veritable blanket of finely atomized water.
A Wing-Top Oxygen-Gas Burner' G . ROSSRobertson UNIVERSITY OF CALIFORNIA AT Los ANGBLES, CALIF.
HE recent adoption of pure natural gas in the local
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city servic-eto this laboratory has rendered glass-working with air-gas mixtures very difficult. Even operations with soft glass require an oxygen-gas blast. For the bending of Pyrex and even the medium sizes of soft glass tubing, an oxygen-gas burner with wing top has been devised as shown in Figure 1. The needle-valve mechanism was removed from each of two old Tirrill burners. These were of the common size which permits the cutting of a 3/J-inch S. A. E. standard male thread, as shown herewith. The v a l v e s w e r e fitted into a short length of 1-inch brass rod bored out and tapped with the S. A. E. thread to fit. A short section of one of the original burner tubes is fitted to the device, while below is provided a length of '/rinch brass rod as a sapport. On the lower end of the support was cut a standard ' / p inch pipe thread, which in turn was fitted with suitahle bushing t o a n o r d i n a r y plumber's galvanized-iron floor flange. A full current of natural Figure 1 gas is first run through one (Scale. fg in. = l i n . ) of the burner valves and lighted. Oxygen under pressure regulation is then cautiously introduced through the second valve, care being taken to have ample pressure-5 pounds or more-brick of the needle valve in order to minimize flurtuations. Enough oxygen is admitted to render the flame barely non-luminous. If an excess of oxygen is used, or the gas is turned off before the oxygen, a n alarming though entirely harmless detonation occurs. The wing flame so produced is very effective in the bending of refractory tubing. With thin-walled tubing it is best to stopper one end, heat the tube until the proper section is constricted and the wall thickened, bend, and then blow out to the original diameter. It was somewhat surprising t h a t an oxygen-gas mixture would not strike back regularly to the mixing chamber in a burner with such ample passageways. Prevention of such 1
Received June 8, 1928.
trouble seems to lie largely in the provision of an appreciahle quantity of paraffin hydrocarbons in the fuel used. The local gas, rated approximately as a 7: 2 (volume ratio) mixture of methane and ethane, and of 1150 B. t. u. value, shows a very slow rate of flame propagation. It is this sluggish action which renders ordinary Bunsen and blast flames so ineffective for the production of localized high temperatures where natural gas is employed. I n the burner described herein, however. the relatively slow flame is turned to good account and permits reasonable control of what would otherwise be a highly explosive mixture. Usefulness on Other Fuels Experiments were carried out to test the usefulness of the burner on other fuels. Pure hydrogen was of course entirely unsuitable on account of rapidity of combustion. A synthetic water-gas mixture of equal volumes of carbon monoxide and hydrogen was also unsatisfactory. The trouble here is due, in part a t least, to the fact that the monoxidehydrogen flame is blue even without admixture of the oxidant, and the operator cannot estimate the proper quantity of pure oxygen to be added. The inclusion of as little as 15 per cent of natural gas improved matters greatly, not only affording flamecolor c o n t r o l , b u t also r e d u c i n g t h e tendency to s t r i k e back. Even g a s mixtures running as high as 75 per cent hydrogen were controllable p r o v i d e d the rest of the fuel was mostly natural gas and the pressure was adequate, as in normal city service. The burner ought to be satisfactory with Figure 2 m o s t coal o r oil gases, or even with well-carbureted water gas. Large-Size Wing Tops I n &w of the large capacity of the burner, one may use wing t,ops larger than the standard article of commerce. Figure 2 shows a simple assembly to serve the purpose. Two triangular pieces of *//sin.sheet brass, from 4 to 5 inches along
INDUSTRIAL A N D ENGINEERING CHEMISTRY
November, 1928
the top, are equipped with two marginal brass shims about 0.05 inch thick. A few channels are milled or cut with a hacksaw on the inner faces of the brass blocks to facilitate the spreading out of the gas current. The whole outfit is assembled and a short hole bored to receive the top of the burner.
off, and the base is removed. This stripped burner is now fitted into a hole bored in the side of the mixing chamber of a second Tirrill burner. Oxygen is admitted from the bottom valve of the main burner, while natural gas is introduced from the side burner. Acknowledgment
Substitute far Burner
If one does not have machine-shop facilities, a simple substitute for the burner of Figure 1 may be improvised. All but half a n inch of the cop tube of a Tirrill burner is cut
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The writer wishes to express thanks t o Gilhome W. J. hlchlillan for the original suggestion leading to the development of this apparatus.
Washing by Decantation’ G. Everett Marsh 5207 DORCHESTER AvB., CHICAGO, ILL.
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HE washing of a large quantity of a precipitate of the A12f0H\B type is practjcallv impossihle unless it is
carried out by successive applications of the decantation method. Such colloids require large volumes of wash water as well 11s much time on account of the slowness with which the precipitate settles. In many case8 it mag be not only desirable but necessary to economize the use of distilled mater, or the operator may desire to keep the labor involved in a series of decantations down as much as possible; and to these ends it is interesting to determine the conditions controlling the most efficient use of wash water. We will assume that the volume of the vessel in which the washing is carried out is Vo, and the volume of the settled precipitate, VI; therefore the wash water decanted is V Z = V o - VI. Assume the initial concentration of the impurity, to be removed by washing, is Co, and let the concentration after the first washing be C1 and after the second, Cz, etc. The fundamental relation is
After n washings the concentration of the impurity in the colloid is the (VIIT’O)“ part of its initial value. The reduction in concentration is I - (V,/VO)”. The volume of the wash water used is nV2 = n(V0 - V , ) . The solution of the problem centers around the determination of the number of the washings necessary to reduce the impurity to a desired amount, and tlie volume of wash water required for the process. I t is a t once clear that the larger the volume of the supernatant liquid or, more correctly, the greater the ratio of this volume to the volume uf the precipitate, the fewer the number of wshings required to reduce the concentration of the impurity to the desired value. When the volume of the precipitate is one-tenth of the total, 1’0, we find that four washings will accomplish as much as six washings when tlie volume of the precipitate is twice as large, and &s much as ten washings when the precipitate is four times as large. In the first rase the volume of the wash water is 4 X 0.9 = 3.6 volumes; in the second 6 X 0.8 = 4.8 volumes, and in the third 10 X 0.6 = 6 volumes. The chart provides immediate answers to all questions relating to the matter in hand. An illustration will suffice. I n a given vessel the precipitate occupies 0.4 of the volume of it. The impurities amount to 25 grams per liter, After 5, 8, and 10 washings, what are the respective amounts of the impurities? After 5 washings we h d 0.01 of 25, or 0.25 1
Received May 2,1928.
gram per liter; after 8 washings, 0.0016 of 25, or 0.04, and after 10 washings, 0.0001 of 25, or 0.0025 gram pcr liter. How much wash water will be required to reduce the concentration of the impurity to 0.001 when the volume of the precipitate is 0.5 that of the vessel? The chart shows that it will require 5 volumes-i. e., 5Vo.
I n cases where the handling of quantities of precipitates of the same kind is a regular procedure, the wash water can be economized by saving that from the last decantations of one batch and using it in the early washings of the next batch.
Correction In the article by D. B. Keyes, Sherlock Swann, Jr., W. Klabunde, and S. T. Schicktanz, entitled “Electrodeposition of Aluminum.” IND. ENG.CHEM.,20, LO68 (1928),the second subheading under “Experimental” should read “Electrolysis of a Tetraalkyl Ammonium Bromide with Aluminum Bromide.” Also in the last line under “Possibilities of Method” on _ page - 1069, boron should be substituted for iron.
