INDUSTRIAL AND ENGINEERING CHEiMISTRY
December, 1927
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.
1349
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.
