Portable Low-Pressure Gas Tanks
small-scale experiments in which a reaction mixture must be protected b y a n inert gas (nitrogen). Gaseous mixtures, such as oxygen-nitrogen, of special composition, are readily prepared with the aid of the gage figures. Refilling is easily accomplished with the aid of pressure tubing, b u t should be entrusted only to thoroughly responsible persons.
G. ROSS ROBERTSON Cniversity of California at Los .ingeles, Los Angeles, Calif.
I
A Capillary Flowmeter
i i LABORATORIES
HUBERT N. ALTE.4 Princeton University, Princeton, N. J.
where scattered workers require small supplies (10 t o 200 liters) of common compressed gases, it is convenient and economical to maintain a central supply service from commercial cylinders and to fill lowpressure tanks for distribution. Although this plan has been used in certain eastern laboratories for a number of years, the tanks now in use are both expensive and inconvenient t o handle. The more convenient truck model shovn in the accompanying illustration is made to order in Los Angeles at lower cost by manufacturers of ordinary compressed-air tanks, for use i n this laboratory. Since the device is not a ready-made article of commerce, specifications p are given below.
T
HE instrument in the figure n-as designed for catalytic TTork in measuring the rate of flow of a liquid immediately before it is vaporized in the cat'alyst chamber. It registers, continuously, the flow of a fen- milliliters per hour. A jacket 15 mm. in diameter supports a capillary tube 20 cm. long, with a bore of 0.1 mm. at the lower end and 2 mm. at the upper end. The float in the inner tube is tapered slightly, and is of colored glass to facilitate visibility. The flow of liquid is indicated in the figure, and requires a constant-pressure head at the inlet and a restriction at the outlet. .4s with commercial rotameters ( I ) , in which this same principle is applied for large rates of flow, the height of the plunger indicat'es the rate of flow.
TANK.Tank to be welded from standard tank sheet iron not thinner than 10 gage. Length 35 to 40 inches, diameter 12 inches. Handle made of 0.625-inch rod or tube mlded a t each end to tank. Two solid rubber wheels, with steel centers, diameter 6 inches, thickness about 2 inches, are supported by a simple steel axle and two steel plates iyelded to tank. When tank stands upright on the floor the wheels clear the floor about 0.125 inch. The tank has one hole in the top, into which is xwlded a standard 0.25-inch I. P. coupling; no other holes are to be provided except those required by law. If such holes are required, the manufacturer shall provide threaded iron plugs to fit. Tank is to be painted or lacquered black, shall cont,ain no oil or other combustible matter, and shall be tested t o 200 pounds pressure before delivery to purchaser. GAGE. Standard commercial air-pressure gage having brass case with glass-covered dial about 2.5 inches in diamet'er, and fitted with male-threaded attachment nipple, 0.25-inch I. P. size. Dial reading 0 to 100 pounds. NEEDLEVALVE. Hoke V-point needle valve KO. 309, brass with Monel needle, 0.25-inch I. P. male threads both ends. HOSEEND. Hoke hose end, all-brass, 0.25-inch I. P. thread, to fit above needle valve. PIPE FITTINGS.One standard pipe nipple, 0.25-1. P. size, length 1 inch, and one standard 0.25-inch I. P. size tee. ASSEMBLY.The threaded fittings are treated with lithargeglycerol paste, which gives a gas-tight joint and is favored over grease or paint from the safety standpoint where oxygen is to be stored. To avoid dangerous errors, bands of bright color should be painted around tanks: green for oxygen, red for hydrogen, yellow for nitrogen.
The accuracy of the meter may be judged from data on the rate of flow of methanol through a particular capillary used by the author. JTitli the float 1 cm. above the lower end of the capillary, flow v a s 1.7 ml. per hour; 6 cm. above the lower end, 4.8 ml. per hour. Design renders the meter insensitive to momentary fluctuations in room temperature.
Literature Cited
Tanks as described have proved particularly convenient for organic combustion analysis (oxygen), and for numerous
(1) Whitwell, J. C., and Plumb, D. S., IND. ENG.CHEM.,31, 451 (1939).
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