ANALYTICAL EDITION
74
Vol. 1, No. 2
less than 99.6 per cent strength is treated with barium oxide. could be recovered. The yield of alcohol using barium oxide At the boiling point reaction 2 proceeds a t an alcohol strength is as good and generally better than that obtained using lime. of 99.4 per cent. Treatment longer than 2 hours gives no The yield of alcohol in run 9 is 92.5 per cent, if a last fraction appreciable concentration of the alcohol (runs 2 and 5). of slightly less strength after 12 hours on the steam cone is One and one-half hours' refluxing with barium oxide is too included. short a period for maximum dehydration. Three hours' General Directions treatment is not better than 2 hours' refluxing (runs 3 and 5 ) . Reactions 3 and 4 were studied by Winkler.* Reaction 3 Condensed working directions for the preparation of dry is very slow with compact metal. If the metal is finely di- alcohol are: vided and the alcohol heated, a rapid reaction takes place. ( a ) Reflux 1000 cc. of 93 per cent alcohol on a steam cone in The reaction is the less a 2000-cc. flask together with 400 grams of barium oxide for 2 rapid the more nearly hours. Replace the reflux condenser by a 30-cm. (12-inch) straight condenser and distil the alcohol l1/2 hours. Yield, a bsol u t e the alcohol. 855 I4 cc. of 99.40 per cent alcohol. More alcohol of slightly less R e a c t i o n 3 is rapid, strength is obtained by distilling for longer periods. however, on 93 to 95 per ( b ) Allow 1000 cc. of 93 per cent alcohol and 500 grams of barium oxide to react cold for 72 hours with occasional shaking cent alcohol. The calL distil as in (a). Yield, 750 cc. of 99.61 per cent alcohol. 2 10 ciuni hydroxide formed and (c) The directions in ( b ) may be duplicated with 20 hours 9 is insoluble, c a u s i n g reaction. Yield, 800 cc. of 99.36 per cent alcohol. .+.0.6 For absolute alcohol reflux any of the products obtained in alcohol to turn milky, but the calcium h y - (a), ( b ) , or (c) on the steam cone with 50 grams of metallic calcium (turnings or wire) suspended in 1 liter of the alcohol droxide does not coagu- by a6 a wire gauze basket hung through the reflux condenser. late. When the reaction of dehydration is complete, as indicated by 0.4 R e a c t i o n 4 attains the formation of a gelatinous gray precipitate of calcium ethylate, appreciable proportions the rapid evolution of hydrogen, and a noticeably exothermal reaction, remove the excess of metallic calcium and distil the 0.2 only with aIcohol above product. One hour is always sufficient for the reaction and 99.5 per cent. much less time is generally sufficient. The product thus ob5 IO 15 20 25 R e a c t i o n 5 follows tained will be found to be absolute. Time in Days rapidly after as well as Advantages of Barium Oxide as Dehydrating Agent Figure 1-Dehydration of Ethyl Alcohol s i m u ~ t a n e o u s with ~y ..with Lime at,Room Temperature 1-The preparation of 99.4 per cent alcohol is accomplished reaction 4. The precipitate in"suspension is coagulated, gelatinous, and grayish with barium oxide using the theoretical quantity of reagent white. Hydrogen is rapidly evolved and may be tested for by refluxing less than one-fifth the time required for the prepaa t the opening of the reflux condenser in the usual manner. ration of alcohol of approximately the same strength using Too great an excess of calcium after reaction 4 has progressed calcium oxide. 2-Theoretical amounts of barium oxide reacting without materially should be avoided. Runs 6 and 7, Table I, show the rates of reactions 4 and 5, addition of heat produce 99.6 per cent alcohol in 72 hours. 3-The yields using barium oxide are in genera1 better starting with 99.56 and 99.34 per cent alcohol, respectively, The yield of alcohol given in Table I is for 1 to I'/z hours' than those obtained using lime. 4-The increased cost of barium oxide over lime is slight distillation. More alcohol could be obtained if more time were given. Counting the water absorbed, the yield of pure and the profitable recovery of the resulting barium hydroxide alcohol for@n 2 is 90 per cent. With a few additional hours' (not) discussed) as well as the saving in alcohol yield lessen heating on-the steam cone several per cent additional alcohol this apparent disadvantage.
E 2
A Self-Regulating Gas Flowmeter' Lyman Chafkfey, Jr. PENNSYLVANIA STATE COLLEGE,STATECOLLEGE,PA.
N THE:course
of some'work upon the vapor phase oxidation of benzene, it became necessary to have a means for obtaining a constant flow of air. The well-known device of a T-tube with one arm opening under water will give an approximate regulation of air pressure, but it is not very accurate. The apparatus described in this paper, although originally constructed as a makeshift to serve while more elaborate instruments were in preparation, proved so efficient that it was used for over a year and with complete satisfaction. It was designed to deliver air a t velocities up to 500 cc. pe; minute, and proved capable of continuous operation over,periods of a week or more. Description of Apparatus
I
The essential parts are an electrically operated gas valve,
a flowmeterlconsisting of a capillary tube with a manometer 1 Received
November 20, 1928.
connected across it, and means for operating the valve by the changes in the manometer level. The valve mechanism is shown in Figure 1. B is an electric bell from which the bell proper has been removed. The valve A is an ordinary automobile high-pressure tire valve. To one of the flat sides of A is soldered a bolt, which serves to fasten the valve to the bell frame. A portion of the end of valve A is cut away so that the stem, C, projects. The valve is so placed that C is hit squarely by the bell clapper, D, when this is depressed. It did not prove necessary to have this clapper vibrate and therefore the wires from the bell's magnet coils were connected directly to the binding posts. However, the end of C should be a little distance from D, so that when the coils are energized the clapper will gather a little momentum before hitting the valve stem. This whole bell-valve combination is suspended in the jar, J, by means of the lead-in wires, H.
April 15, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
Air entering the apparatus is carried by means of the rubber tube E directly to the “tire end” of the valve A . When the valve is open, the air passes into the jar, J, and out through the exit tube, F. The stopcock, G, serves as a by-pass valve, and makes it possible to obtain a much larger flow of gas than would normally pass through A . T h e a i r f r o m t h e valve is run G -, through a 20-liter bottle to smooth out the irregularities in flow caused by the intermittent operation of the valve. From this reservoir the air passes to the flowmeter shown in Figure 2. Here 0 is the capillary. The flask, J K , contains mercury, below the level of which dips the end of the manometer tube, L. I n order to increase the sensitiveness of the apparatus, L is inclined a t a small angle to the horizontal. If the angle whose sine is l/la-about 4 . 5 degrees-is chosen, the pressure read along L in centimeters of mercury is the same as the pressure that would be indicated by a vertical water manometer. A centimeter scale may be glued to the back of L. If the level of mercury in the flask K varies fairly uniformly with the change in level of the mercury in the manometer tube, which will usually be the case, the use of a fixed scale will not change the calibration curve (manometer scale readings plotted against rates of flow) from an approximately straight line. The upper end of the tube L is large enough to take a rubber stopper, M , through which passes a long glass tube of small diameter, N . Through the lower end of N there is sealed a tungsten or platinum wire, p * (In the drawing no distinction is made between the wire point, P, and the tube N . ) The hole in the stopper M is lubricated with glycerol so that the tube N will slide readily. The capillary 0 should be placed above the manometer as indicated, so that if the valve ever sticks open the back pressure of mercury in the vertical tube connecting the upper part of L with 0 will counterbalance the air pressure and prevent mercury from being blown entirely out of the manometer. Electrical connection with the mercury reservoir is made by means of the iron wire, Q.
75
experiment. When the apparatus is not in use, the valve circuit must be broken. Performance
The operation of the apparatus should be clear from this description. If the supply of air or gas available has more than a moderate pressure, the apparatus should be protected by some sort of safety valve, such as a tube opening under a meter or two of water. The efficiency of this self-regulating flowmeter is indicated by its performance under the conditions in which it was actually used. As employed in the work for which it was designed, the flowmeter was operated to furnish a constant stream of air, which was passed through a constant thickness of liquid benzene heated to a constant temperature in a thermostat. It was especially desired to vaporize under constant conditions a definite weight of benzene in a given time, and to have the results reproducible. During the course of the work a number of blank runs were made in which the vaporized benzene was condensed under standard conditions, and weighed. This served as a check on the functioning of the whole set-up, of which the flowmeter was only a part. However, the consistency of the experiments indicates the dependability of the flowmeter itself. The accompanying table gives the results of some pairs of these blank runs made over a period of 8 months. In most cases a number of other experiments intervened between the two blank runs of a pair. It will be understood that only the two runs of a pair are to be compared with each other. I n going from one pair to another, various changes, such as in the flowmeter setting and temperature of benzene, were made. DURATION RUN
H*W~
4
Checks o n Flowmeter Operation WEIGHT BENZENE DURATION WEIGHT op BENZENE RECOVERED RUN RECOVERED Grams Hours Grams (a) 270 8 (a) 365 ( b ) 272 ( b ) 365
24
( a ) 165 ( b ) 165
8
( a ) 393 ( b ) 393
7
( a ) 415
8
(a) 378
( b ) 414
8
( b ) 379
( a ) 340
( b ) 342
A Convenient Method for Preparing Na-K Alloy’ Thomas Midgley, Jr., and Albert L. Henne BAKERLABORATORY OF CHEMISTRY. CORNELL UNIVERSITY. ITHACA, N. Y.
HEN maximum reactivity, a t relatively low tempera-
Figure 2
The flowmeter circuit operates a 250-ohm telegraph relay, which in turn operates the air valve. The relay contacts are so arranged that when the flowmeter circuit is open the valve circuit is closed. The relay draws so little current that it is not necessary to connect a condenser across the flowmeter circuit. It may be necessary to clean the point P every 6 months or so. On the other hand, the bell coils in the valve mechanism draw a quantity of current, and therefore the batteries in the valve circuit, if batteries are used, must be watched to see that they do not go dead during an
ture, is desired of an alkaline metal, the liquid sodium-potassium alloy is very useful. The most common method of preparation is t o melt the metals together under kerosene. This method is not satisfactory, for it tends to divide the alloy into small particles coated with dirt. The alloy is easily prepared by placing freshly cut sodium and potassium in slightly wet ether and slowly agitating. It keeps clean under ether, and may be pipetted from the bottom of the container in substantial purity. Although the. alloy catches fire when exposed to air and must consequently be handled with care in the presence of ether, experience has shown that this association is less dangerous than the association of the alloy with benzene, since the rapid evaporation of the ether has a cooling and a blanketing effect, which reduces the tendency of the alloy to ignite. 1
Received December 7, 1928.
