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flow through the siphon and the supply pipe to the lift, from which it is forced into the tank above. A solution is easily transferred from one vessel to another as shown in Figure 4, and the arrangement may be used for various purposes. By a similar device an air-jet compressor may be made to supply the compressed air. Automatic control may be applied to the lift by employing a float to operate a snap valve in the compressed-air line. This type of valve remains either entirely open or
Vol. 19, N o . 12
entirely closed and has no intermediate position during the travel of the float. The air-jet lift is continuous in operation after once being started as long as compressed air and water are supplied to it. Although the efficiency is low, this is offset by the advantage of having no moving parts to wear out, by the simplicity of the apparatus, and its ability to handle materials which could only be handled with difficulty or not a t all by ordinary pumps.
A Simplified Capillary-Tube Plastorneter’ By J. L. S t . John THESTATE COLLEGE
OF WASHINGTON, PULLXAN, W A S H .
INCE the classic work of Bingham,2in which he resolved
S
the property of plasticity into two components, yield value and mobility, a variety of capillary-tube instruments have been d e ~ i g n e d ~for , ~ , use ~ with different materials. The majority are of the vertical type involving a varying pressure due to varying hydrostatic head during flow. Bingham and Murray3 designed a horizontal type of capillary-tube plastometer and Kelly6 simplified the calculation so that pressure-flow curves might be more easily constructed. This plastometer as used by Kelly required a machined and nickel-plated cylinder and guard for the capillary tube. I n working with biological materials, the author has used a simplified type of this plastometer, which may be constructed in a few hours from materials found in any laboratory a t a negligible cost. Description
The cylinder is made from an ordinary 125 by 16-mm. soft-glass test tube, cut to a length of about 70 mm. and relipped. A side tube of soft-glass tubing 5 mm. in diameter and about 60 mm. long is blown into the shortened test tube as near the bottom as is convenient (10 to 15 mm.). Other sizes of test tubes may be used depending on the requirements of the work. A length (76.5 cm.) of heavy-wall capillary tubing (7 mm. external diameter), with the desired internal diameter, is inserted into a NO. 0 rubber stopper cut to a length of about 1 cm. This stopper is securely inserted into the test tube after it has been filled with the material to be studied. The side tube of the cylinder is then connected to the pressure tank by rubber tubing. The tubing is closed with a pinch clamp, sometimes used in conjunction with a screw clamp. A rubber tube is connected to the exit end of the capillary and the apparatus is placed in the constant-temperature bath. This apparatus may conveniently be used in a Freas largesize sensitive water thermostat by removing one of the heating lamps and placing the plastometer cornerwise in the bath. The less expensive bath described by Bingham and Murray3 may be constructed and heated with knife heaters, using a high-speed turbine stirrer and a Harvey thermoregulator. 1
Received June 6, 1927.
* Bur. Standards, Sci. Paper 278 (1916). Bingham and Murray, Proc. A m . SOC. Testing Materials, 28, 655 (1923). 4 Cooke, J . A m . Ceram. SOL., 7 , 651 (1924); Herschel and Bulkley, THISJOURNAL, 19, 134 (1927); Moness and Glesy, J . Phys. Chem., 29, 1282 (1925); J. A m . Pharm. Assocn., 16, 39 (1926); Sharp, Cncal Chcm., 8 , 40 (1926). 6 Bingham, “Fluidity and Plasticity,” McGraw-Hill Book Co., New York, 1922. e “Colloid Symposium Monograph.” Yol. 111, p. 303, Chemical Catafoi’Co.,New YoFk, 1 9 5 . 3
The pressure is read in centimeters of water and the connection between the test-tube cylinder and the capillary has been found to be sufficiently tight to allow the use of pressures as high as 200 cm. of water. Much higher pressures could probably be used. A 15-liter tank is placed in the pressure line to prevent rapid fluctuation of pressure. The higher pressures are obtained by use of the laboratory pressure system. Calibration of Capillary Tube
The capillary tube is rtccurateIy laid off in 10-cm. sections with a Vernier caliper beginning a t the end inserted into the rubber stopper, the divisions being marked with a file or diamond point, The visibility of the division lines may be increased with a thin line of black paint. Small strips of gummed labels may be pasted opposite the marks on the tube to facilitate observation. Thermometer tubing may also be used in place of regular capillary tubing. I n calibrating the tube, mercury is drawn into it in amount sufficient to fill the capillary for a little over 10 cm. The exact length of this mercury column is determined in each 10-cm. section of the tube. The mercury is then weighed and ite volume calculated. From these data the volume, AV, and the average radius of each section of the tube are calculated. Using Kelly’s formula ?rR4gP 8(
y)
a constant is calculated for each section of the tube, which includes all of this formula except the value for P. This constant is then multiplied by tho observed pressure for each determination. I n practice it is convenient to reduce the amount of calculation by maintaining the pressure within narrow limits and then calculating a series of-constants for use within these limits. Manipulation
The cylinder is filled with the material to be studied, the capillary tube is attached, and the apparatus is allowed to come to the temperature of the bath (25” C.). The size of capillary and the pressure used should be sufficient to cause a uniform, but not too rapid, flow. When the apparatus has reached the temperature of the bath, the pressure is released and the time noted as the column of liquid passes each division of the capillary tube. Zero time may be taken a t the first division where the flow is not too rapid to permit accurate timing. A split-second stop watch is necessary for this. From the stop-watch readings the time of flow, At, for each division is determined. From this value and the volume of each division of the tube, AV, the rate of flow A V l A t is
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calculated for each of the sections. According to Kelly the rate of flow, A V / A t , should be plotted against the value irR4gP 8(1+)
The tangent of the angle thus formed is defined as the mobility of the material studied. The tangent of the angle may be obtained graphically, but is preferably calculated by the method of least squares, using the formula given by Mellor.’ The yield value may also be calculated by the method of least squares. A rapid calculating machine is essential if many determinations are made. Mobility Determinations Mobility determinations have been made on a number of biological materials using the apparatus described. The 7
“Higher Mathematics for Students of Chemistry and Physics,”
D. 326, Longmans Green & Co., London, 1916.
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results obtained with this instrument are compared with those obtained with the Bingham and Murray plastometer in Table I, which gives data obtained on duplicate flour-inwater suspensions prepared by mixing 30 grams of flour and 70 cc. of water and gently working in a mortar, a small portion a t a time. Table I-Mobility of Flour- Water Suspensions FLOUR SIMPLIPIBD PLASTOMETER BINGHAM-MURRAY PLASTOMETBR No. 1 2 3 Av. 1 2 3 Av. 1 0.759 0.714 0.780 0.751 0.731 0.742 0.777 0 . 7 5 0 2 0.593 0.648 0.688 0.643 0.667 0.793 0.693 0.718 3 0.732 0.761 0.747 0.740 0.755 0.747
Table I1 gives mobility determinations on reconstituted dry-skim milk. Table 11-Mobility Milk 1 1 0.51 2 1.95
of Reconstituted Dry Skim Milk 2 0.50 1.85
3 0.56 1.71
Av. 0.52 1.84
Hydraulic Lift for Gas Analysis Apparatus’ By E. J. Tauch DEPARTMENT OF CHEMICA~ ENGINEERING, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS.
A
SIMPLE and flexible device for mechanically raising and lowering the mercury bulb of a gas analysis apparatus, or other apparatus in which mercury is used for displacement, is shown in the accompanying diagram. It is especially useful where a large number of analyses must be made, or where the operator must give most, of his time to the control of other apparatus. The only attention required is an occasional shift of a stopcock lever and the leveling and reading of the mercury level between absorptions. Water pressure supplies the operating power, raising and lowering a plunger which carries the bulb support. With the three-way stopcock in one position, water flows into the cylinder and raises the plunger until the overflow pipe is reached. During this up-stroke the gas to be analyzed has been forced into one of the pipets. It will remain here until the three-way stopcock is shifted to the other position. The weight of the plunger and the mercury now forces the water out of the cylinder and into a drain, the gas being drawn back into the buret at the same time. This operation is repeated as many times as is desired by merely shifting the stopcock lever back and forth. When the absorption has been completed the mercury is leveled by moving the bulb up or down on the plunger rod. The movement of the plunger is smooth and uniform. By moving the stopcock to an off position the plunger can be stopped during any part of the stroke. The speed of travel is readily controlled by two needle valves, one controlling the incoming water, the other the outgoing water. Once this adjustment is made it is necessary to operate only the stopcock to obtain a uniform motion. The mercury bulb can be set to a definite position on the plunger rod such that there is never any danger of forcing some of the mercury over into the pipets. The brass cylinder should be about 2.5 cm. inside diameter. Its length will be determined by the length of the buret with which the apparatus is to be used. An additional allowance of about 15 cm. should be made for connections. A plunger rod about 1 cm. in diameter is sufficiently rigid. Its length 1
Received June 16, 1927.
should be such that, with the plunger at the bottom of the cylinder, the rod will project several centimeters above the guide. A cup-shaped leather washer, such as is used in an automobile tire pump, serves very satisfactorily as a plunger. If desired, the device can be made entirely automatic in operation, with the exception of leveling and reading. A simple mechanism for shifting the stopcock lever a t the end of each stroke, either mechanically or electrically, can be constructed for this purpose. The hydraulic lift not only e l i m i n a t e s the work of raising a n d l o w e r i n g the heavy mercury bulb, but it also gives more EDLL WATER a c c u r a t e results in D a n a l y s i s because of 2 5CM B CY more consistent operation. There is always a tendency to raise and lower the bulb too rapidly when this must be done by hand. The resulting irregular pressure differences increase the error resulting from any small leaks which may be present in the apparatus. The lift is particularly useful in making combustion analyses, in which a very slow and uniform flow of gas into the combustion pipet is desirable. The needle valves, for this use, can be adjusted to give an almost imperceptible motion of the plunger. Its performance in practice has proved so successful that it has been installed on all fixed gas analysis apparatus ip this laboratory.
