ANALYTICAL EDITION
158
Several such calibration curres are taken for different fuel gases, as shown by curves ( 2 ) , (3), (4), and (5). Then if it is desired to determine the percentage of any fuel gas in air, the proper curve is selected by the determination of K r for pure fuel gas, as above. Then K , is determined for the unknown mixture, and by reference to the proper curve the unknown air-gas ratio, or percentage of fuel gas, is a t once found. For any one general type of fuel gas, a family of curves can be drawn by taking only a few measurements w i t h k n o w n gas-air mixtures. Thus this family of c u r v e s can be used SUDEWIRE READING- K o sa0 as above, the exact Figure 6-Calibration Curves v a l u e s of t h e unknown air-gas ratio being determined by graphical interpolatihns bettveen two adjacent curves if necessary.
Vol. 1, KO. 3 Precision of Apparatus
No definite statement can be made of the accuracy of the apparatus, since the composition of the gases analyzed varies over wide limits, and all errors vary with the gas composition. However, the accuracy is of the order of *0.2 per cent of gas, on the gas-air scale. The precision, of course, varies with the type of galvanometer used, as well as with bridge current and slide-wire shunt employed. In general the precision is d 0 . 1 per cent of gas, on the gas-air scale. Other Uses for Apparatus
The apparatus is not confined to measurements of fuel-air ratios, but can be adapted for many laboratory and industrial applications in which a compact apparatus is desired. It can be calibrated for a wide variety of gaseous mixtures and used in numerous research problems and in tests of various equipments. It has all the advantages of the thermal conductivity apparatus-speed of operation, freedom from absorbing chemicals, high accuracy, and instant adaptability to various problems of analysis. Literature Cited (1) Palmer and Weaver, Bur. Standards, Tech. Papev 249 (1924). (2) Peters, U. S.Patent 1,504,707 (1924).
A New Plastometer' E. Karrer THE B. F. GOODRICH COMPANY, AKRON,OHIO
A
T T H E Swampscott meeting of the
AMERICAN CHEMISOCIETYan analysis was given of the meaning of plasticity when this term names a property of solids that concerns the molding of plastics such as rubber.* -4function for plasticity was deduced with some suggestions on the adoption of a C. G. S. unit of plasticity. Also, a design of a plastometer, based upon this analysis, was outlined. It is the purpose of this paper to give a full description of such a plastometer. CAL
Original Plastometer
d detailed drawing of the instrument as first conceived in February, 1927, is given in Figure 1. The rubber sample, 1, in the form of a cylinder 1 em. long, 1 sq. em. cross section, is held between two vertical round rods, A and B, which will be designated as upper and lower plungers. These plungers consist of contacting end caps, 15, 20, of steel mounted upon porcelain tubes, 19, which in turn are cemented into sockets 16, 21. The lower socket, 21, slides through a bushing, 22. Its nether end is cut obliquely, and by means of a spring is pressed into contact with the surface of a cylindrical wedge, 23, movable in and out by means of a drum nut, 25, fitted t o the threaded end, 24, of the wedge. The height of the sample may be read to 0.001 inch off the scale on the drum nut, 25. The upper socket, 16, slides in a tube, 17, and has a bearing shoulder for the spring, 9, called the force spring. The upper plunger, together with other parts bearing upon it from above, is carried by a light spring, 27. Toggle joint 8 is actuated by a power spring, 10, that is restrained in a tube and exerts directly against the head, 13, Received June 18, 1929. This analysis and some preliminary d a t a obtained with this instrument will appear in the August issue. 1
2
of a double compression rod, 12. This power spring is compressed or charged by the levers, 11, and may be released by a slight motion of a latch 2. When such release of the power spring takes place, the piston, 13, pushes the toggle from the flexed to, and through, the vertical position and depresses the piston, 18, a constant amount, and compresses the force spring, 9, to an extent depending upon the hardness ( f the sample. The amount of compression of the force spring and sample is indicated by the gage hand, 6, which carries a friction hand, 14, to its maximum position. The position of the friction hand may be read later to obtain the extent to which the sample has been compressed and with what force this has been brought about. The gage has connection with the sample by means of an extension rod, 4, of glass or invar. The gage in the present apparatus was especially constructed to fit the situation. Its essential parts were the gears, 7 , of a small pressure gage. To control the time of one stroke-that is, of the time during which the compression is applied-the power spring, 10, was caused to expand against the dampening resistance offered by an ordinary Yale door check, 3. This interval turned out to be about 0.6 rather than 1 second as intended. The procedure is as follows: A sample with a plate, 5, laid upon it, is inserted between the plungers. The wedge scale reading indicating the height is recorded; the latch lever, 2, is pushed to release the power spring, 10, which had been compressed before the sample was inserted. The resulting downward motion of the upper plunger depends upon the softness of the sample, and is readable from the position of the friction hand, 14. The stop watch is started the moment the motion of the friction hand ceases. The traveling hand, 6, is observed in its motion backwards and its position read after 5 seconds. From the three scale read-
INDUSTRIAL A N D EA-GINEERIXG CHEZUXTRY
July 15, 1929
Figure 1-Sectional
View of Original Plastometer
ings thus recorded the plasticity may be reckoned. The dial reading of the maximum hand gives directly the amount of compression, h - hl, where h is the original height, hl the height under maximum compression. Next, the force, F, that has been exerted to accomplish the compression is also obtained by subtracting the dial reading given by the friction hand from the dial reading which indicates a perfectly soft body-that is, the reading which indicates that the compression spring has experienced no resistance from the sample and was free to follow to the extreme downward position demanded by the toggle. The amount of the compression, which is retained a t the end of 5 seconds, is h - hz, where hz is the height 5 seconds after compression. I n accordance with the definition that has been given in the analysis, plasticity is the product of a softness function and a property termed retentivity. It may be expressed as follows: P
K
X softness X retentivity h - h i X h2 - h ="K h - h = K X h Fh - h 1 hF =
159
where K is a constant depending upon the units and apparatus. In calculating the absolute values from the readings of this instrument, the average value of force, F,is used. Automatic Plastometer
The plastometer that has just been described has been modified in certain respects t o eliminate the personal element to a great extent and to make the control of the time interval more positive. It was originally intended to make this instrument entirely automatic and autographic. The autographic feature has been eliminated from considerations of practicality. A gage has been substituted, whose reading, however, has been made much simpler as will be seen below.
Figure 2-Sectional
View of Automatic Plastometer
Figures 2, 3, and 4 depict in sectional, front, and top views the instrument with these changes. The toggle joint, 1, is operated through the scotch yoke and eccentric, 2, by means of a sawtoothed clutch, 3, and 8 system of gears, 4, 5 , 6, and a synchronous motor, 7. The gearing is such that the toggle, 1, will go through one-half cycle of operationthst is, from the extreme left to the extreme right positions in 1 second. It is positively driven in both its to and fro motions so that it does not, as in the previous instrument, release the force spring, 8, suddenly. The gage, 9, is, as in the previous instrument, furnished with a friction hand, 10, which retains the maximum position t o which the indicating hand moves. The indicating hand may be read a t any time after the maximum compression has been accomplished. To facilitate this, a light signal is provided by means of lamps, 11. This signal, flashing every second, is distinctly visible while the indicating hand is being followed in its motion backwards. The making and breaking of the signal circuit are accomplished by the use of Ford induction coil contacts, 14, and a hard-rubber cam, 12, whose shaft is geared, 13, to that of the scotch yoke. The engaging and disengaging a t the clutch, 3, depends upon the lever, 17, which when depressed raises a pin out of its groove in a sleeve, 22, and allows the driven half of the clutch to slide into engagement with the driving half. As long as there is engagement the timing shaft will be rotated by means of the gears, 13. The yoke shaft may or may not be rotated depending upon 'whether or not the sleeve, 15, is allowed to slide into engagement with the end of the clutch sleeve just mentioned. When the lever 16 is depressed, such sliding of this sleeve will take place. When the levers, 16 and 17, are depressed momentarily, the scotch yoke shaft will make one-half revolution while the signal shaft, 18, will make one complete revolution
AL EDITION
160
Vol. 1, K O . 3
tions of the signal shaft may take place. This means that a sample may be compressed for 1 second and its recovery observed after one or any whole number of seconds. The gage, 9, is of a special design. Its stem, as well as other parts, is hollow. It has only a small hair-spring to take up lost motion. This makes for extreme lightness and a small load upon the sample. The dial of this gage is graduated to 0.001 inch; the extreme travel of the stem is 0.5 inch. To lift gage extension rod, 4, off the sample, the eccentric wheel, 28, bearing against a lifting rod, 29, is provided. To control the temperature of the sample, 19, the upper and lower plunger, 20, 21, are surrounded by an oven, 23, equipped with thermometer, 24, and thermostat, 25. The samples are inserted and removed through a small door. Illumination within the furnace is provided for by a small lamp, 26, above the small door, 27, and attached to the large door. Only stocks that do not recover completely in 1 second may be studied with this instrument.
A Modified Pauly Receiver' J. B. Brown DEPARTMENT OF PHYSIOLOGICAL CHEMISTRY,OHIO STATE UNIVERSITY, OHIO COLUMBUS,
modified Pauly receiver for use in fractional vacuum A distillation is shown in the accompanying photograph. The receiver is constructed from a standard 250-cc. Pyrex
Figure 3-Front
View of Automatic Plastometer
By prolonged depression of the levers, 16 and 17, any number of revolutions may be allowed-that is, any number of the to-and-fro motions of the toggle, any number of compressions, and any number of light signals may take place. By momentary depression of the yoke-sleeve lever, 16, and prolonged depression of the clutch-sleeve lever, 17, only one motion of the toggle is allowed, but any number of revolu-
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suction flask. In the base of the flask are blown six depressions about 20 mm. in diameter. To each of these is s e a l e d a piece of 12-mm. Pyrex glass tubing with 2mm. walls. Each of these legs is 120 mm. long and slopes outward on a line parallel to the side walls of the flask. This arrangement makes possible the use of a 500-cc. receiving flask on each leg. The adapter is made from ordinary glass, the lower end being a t least 8 mm. outside diameter, in order to cut down bubble formation and spattering into more than one depression a t the bottom of the Aask. A similar receiver w i t h eight legs may be made from a 500-cc. Pyrex suction flask. The receiver w o r k s m u c h more successfully in the laboratory than any Pauly receiver that the writer has been able to obtain on the market. The glass blowing on the apparatus illustrated was done by R. B. Leonard, of the Department of Chemistry. 1 Received
Figure 4-Top
View of Automatic Plastometer
April 6, 1929.
Dutch Scientist Aids in Defining Atomic Spectra-The Bureau of Standards, with the assistance of T. I,. de Bruin, of the University of Amsterdam, who has completed his work in the Department of Commerce, has established a record in scientific research by defining and explaining no less than six different spectra in a period of ten months. These include the halogenschlorine, bromine, and iodine-the heavy rare gases-krypton and xenon, and the more familiar but deadly metal, arsenic.
