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INDUSTRIAL AND ENGINEERING CHEMISTRY
Method of Reading Hydrometers Fill a clear glass jar or cylinder having a height equal to the length of the hydrometer and an inside diameter a t least 1 inch greater than the diameter of the hydrometer bulb to within about 2 inches of the top with the turpentine to be tested; place a thermometer in the jar, and set it on a table in a sheltered place. Carefully immerse the hydrometer in the turpentine to a point slightly below that to which it naturally sinks and then allow it to float freely. Be sure the hydrometer is not in contact with the jar or the thermometer. When the temperature as registered by the thermometer has become stationary and the turpentint. and the hydrometer are free from air bubbles and are at rest, place the eye slightly below the plane of the surface of the turpentine (Figure 2, left) and raise the eye slowly until this surface seen as an ellipse appears t o be a straight line (Figure 2, right). Take the reading of the instrument at the point at which this line cuts the hydrometer scale ( 2 ) . The third decimal on the scale must be determined by interpolating (estimating) from the smallest division on the scale. Record the reading of the hydrometer and the thermometer (first making corrections if instruments have been standardized). If the kmperature of the turpentine is not BO". the weight per gallon at 60" and other temperatures may be obtained from Table I or Figure 3.
Vol. 13, No. 2
An enlargement of Figure 3 on millimeter cross-section paper map be obtained by writing the Naval Stores Research Division, Bureau of Agricultural Chemistry and Engineering, Washington, D. C Khile hydi ometers indicating pounds per gallon are not a t present listed by instrument makers and apparatus supply firms, a number of instrument makers have indicated that they can furnish instruments suitable for use with turpentine. This type of hydrometer of suitable range with accompanying tables or graphs should be useful for the weightvolume conversion of mineral oils and other liquids.
Literature Cited (1) Bearce, H . W., Bur. Standards, Tech. Paper 9 (April, 1912). (2) Natl. Bur. Standards, "National Standard Petroleum Oil Tables", Circ. C410, p. 4 (March 4 , 1936). (3) Smith, W. C., and Veitch, F. P., U. S. Dept. Agr., Circ. 110 (Feb., 1930). (4)
Veitch, F P., and Grotlisch, V. E., U. S. Dept. Agr., Bull. 898 (Nov., 1920: revised Sept., 1921).
Rapid Method for Calibration of Flowmeters IIERMAF; J. &lEUHON1, Stanford University, Calif.
I
T OFTEX becomes necessary to construct and calibrate a flowmeter or t o calibrate a capillary tube for a flowmeter
with interchangeable capillaries in a laboratory where no calibration apparatus is immediately available. Under such circumstances the most useful method of calibration for laboratory meters using relatively low pressures consists of displacement of the gas by a liquid, thus forcing the gas through the flowmeter. The following advantages are obtained : simple construction from ordinary laboratory apparatus; precision, accuracy, and rapidity of calibration measurements due to upward displacement of gas; and economy of calibrating liquid (if other than water is used). Most methods (1) displace a liquid, such as water, by the gas after the gas has passed through the flowmeter. If a t the end of a known time the volume of liquid used is measured, the volume of gas flowing per unit time can be calculated. However, in such techniques downward displacement of liquid tends to create a back pressure which changes the rate of flow as the head of the liquid changes. As i t was necessary t o carry out a number of calibrations, the following procedure was devised: An arrangement B and C (Figure l), giving a constant head (or any such device), allows w t e r to run into a calibrated mixing cylinder of 1- or 2-liter capacity. B may be an inverted 2-liter bottle with the bottom removed. The stream of water is controlled by means of a stopcock or screw clamp, A ; a stopcock is more satisfactory. The water displaces the sample of gas in the cylinder, forcing it through the flowmeter. Since the inlet tube into the cylinder is bent, there is no splash, and readings are easily made on the cylinder. When A is adjusted to a convenient pressure differential, indicated by the liquid in the flowmeter, a stop watch is started and the level in the cylinder is noted. This is usually about 200 to 300 ml., so that a large cylinder calibrated like a graduate of the same size is desirable. From these measurements the volume per unit time flowing through the flowmeter can be calculated. This operation is repeated for various pressure differentials of the indicating liquid in the flowmeter by regulating A . It is convenient to construct a graph, plotting pressure differential against volume per unit time. 1 Present address, U. S. Food and Drug Administration, Federal Office Bldg., San Francisco, Calif.
FIGURE 1 The design of the apparatus permits, with slight modification, use of a n y gas desired. If water is undesirable as a calibration liquid, mercury or oil may be substituted, the apparatus being designed so that there is no loss of liquid. The dropping mercury method, on a smaller scale than herein described, is especially adapted to the calibration of sensitive meters, measuring the continuous flow of small quantities.
Literature Cited (1) Smith, G . W., IND. ENQ.CAEM..-4nal. Ed., 4, 244 (1932)
