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.
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
HEN maximum reactivity, a t relatively low temperature, 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.
