AXALYTICAL EDIT'ION
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LIGNITEFROM DICKINSON,N. D.-This sample had the following proximate analysis: moisture 30.9, volatile matter 47.3, fixed carbon 13.1, ash 8.7 per cent. The results obtained by different methods were as follows: Per cent 3 1 . 8 and 30.9 3 0 . 5 and 3 0 . 8 32.5 and 3 0 . 5
Drying a t 108' C. Xylene Methanol extraction
Conclusion
The extraction method shows a small but fairly constant higher Value for the water Content than that obtained by extraction by xylene, this difference changing only very slightly with the length of time of extraction, the amount of final water content of the methanol, and the species of coal. The values obtained check one another a t least as well as
Vol. 1, No. 3
those obtained by any other method. The essential advantages found in the new method are fast working, easy cleaning of the apparatus, and the possibility of working a t room temperature. ' Of course, before this new method could be considered as a substitute for the A. S. T. M. method, it should be applied to a considerable number of different types of coal and other substances, though the widely different species of coal to which it already has been applied suggest that it will work in any case. Literature Cited Am. SOC. Testing Materials, Standards, 1924, pp. 901 and 1016. Marcusson, Mitt. kgZ. Versuchsanstalten, Bei,lin, aa, 48; Chem. Zentv., 75 11, 962 (1904) ; Mitt.kgl. Matevialpriifungsaml Gyoss-Liclzleufelde West, as', 58; Chem. Zentu., 77 I, 289 (1906). (3) Orth, z , angeru. Chem,, 33, 492 (1926). (4) Piatschek, Buaunkohle, 27, 49 (1928).
(1) (2)
An Improved, Air-Gas Ratio Apparatus' Crandall Z. Rosecrans LEEDSA N D NORTHRUP COMPANY, PHILADELPHIA, PA.
HE apparatus to be deA gas-analysis apparatus of the thermal conductivity pend on the thermal conducscribed is for the detertype is described, particularly designed for measuretivity of the gas. By makmination of the volume ments of ratios of air to fuel gas, where the fuel gas may ing the wire of platinum, or percentage of any one gas or be of any composition. The apparatus is also adaptable other material with a submixture of gases in air or in for general gas laboratory work, where concentrations s t a n t i a l temperature coeffiof known gases are to be determined. I t consists of a cient of electrical resistance, any single gas. It operates thermal conductivity cell mounted in a constantit is possible to measure the on the well-known thermal conductivity principle, detemperature block controlled by a bimetallic thermowire temperature by electrical scribed by Palmer a n d stat, and an improved Wheatstone bridge gas-analysis means. Hence the thermal circuit. conductivity of the gas surWeaver ( I ) , * and is a modirounding the wire can be defication and improvement of the original Bureau of Standards device. While the thermal termined in relation to some standard gas, such as air. conductivity method for gas analysis is quite widely used, a Description of Apparatus brief description of the fundamental theory will be given here. A thermal gas-analysis cell is shown in Figure 1. It conGases differ markedly in their ability to conduct heat. If the conductivity of air is taken as unity, conductivities of sists of a brass block in which a 3/&ch (0.95-cm.) hole is other -gases range - from that of carbon disulfide vapor a t drilled. Mounted axially in this hole i i a platinum wire, 0.284 to that of hydrogen 0.002 inch (0.005 mm.), which is kept stretched by a small btcr nda rd Tube S c A n a , y s ; n g Tube a t 6.95. Gaseous mix- helical spring a t the lower end. The wire is electrically \r t u r e s . of course, have connected to the block a t the conductivities which de- lower end and is insulated a t pend on their constitu- the top by a glass-platinum ents and the relative seal. The wire is heated to a a m o u n t s of each con- temperature between 100 and stituent. Now, if a fine 200' C. by electrical energy; wire is supported in a substantially all the heat loss tube and heated by an from the wire takes place by electrical current, practi- conduction through the gas. A complete gas cell consists Meos u r n g W i r as cally all of the heat will b e l o s t b y conduction of two such tubes, both drilled A through the gas. Thus in the same block. One tube is the equilibrium tempera- sealed up with dry air (over ture of the wire will de- P,OJ as a standard. The other tube has connections through W k
T
c
O
i
l Received April l l , 1929. Presented before the Division of Gas and Fuel Chemistry a t the 77th Meeting of the American Chemical Society, Columbus, Ohio, April 29 to M a y 3, 1939. Italic numbers in parenthesis refer to literature cited Gas-Analysis Cell a t end of article.
*
F i g u r e 1-Thermal
which the unknown gas to be F i g u r e 2-Gas-Analysis C i r c u i t analvzed can be admitted. T i e simple gas-analysis circuit in Figure 2 illustrates the method of measurement. S is the standard (sealed) wire and X the analyzing wire. A and B are resistances of zero temperature coefficient. K is a slide wire which can be adjusted to balance the Wheatstone bridge, the balance point being shown by the galvanometer G. A 4.5-volt battery supplies
July 15, 1929
INDUSTRIAL AND ENGINEERIiVG CHENISTRY
energy to heat the wires. Assuming that the two wires S and X are identical in resistance and in thermal environment, with dry air contained in both tubes, a balance point will be obtained a t the mid-point of the slide wire. Now if the air in the tube X is replaced by a gas of different thermal conductivity, the contact on the slide wire K must be moved to a different point to Thermometer rebalance the b r i d g e . Thus readings on the scale attached to the s l i d e wire K , a f t e r proper c a1i b r a t i o n , would be functions of t h e g a s conductivity, and hence of the concentrations of the unknown gas. Since the t h e r m a l conductivities of various gases c h a n g e a t d i f f e r e n t r a t e s with temperature, it is necessary to maintain the gas-analysis cell a t constant temperature, within limits fixed by the accuracy of measurement desired. This particular a p p a r a t u s embodies a small bimetallic strip thermostat, combined with an electrical heater. These Lwo Figure 3-Thermostatic Block devices, together with the thermal gas cell, are contained in a single heavy block of metal which, by the action of the thermostat, is kept a t 35" * 0.4" C. Figure 3 shows the construction of the thermostatic block, adapted from a design of the Bureau of Standards. Figure 4 shows the completed apparatus, while Figure 5 gives the circuit diagram. The large cylindrical hood carries the slide wire contact, and also a scale of 1000 divisions, each of 0.216 inch (0.55 cm.). The cell, in its thermostatic block, is mounted on the upright panel a t the rear of the instrument. The panel also carries a milliammeter and rheostat for adjusting the bridge current to the desired value. A small pilot lamp, observed through a hole in the panel, is in series wit,h the thermostat, and by its switching on and off calls attention to the proper operation of the thermostat. The temperature a t which the thermostat controls may be set by the knurled screw on the front of the block. Ordinarily the temperature is maintained 5" or 10" C. above room temperature. The resistance E, normally 0.1 to 0.3 ohm, is a so-called current compensating coil (g), and is intended t o make the two wires electrically identical for all temperatures. It is determined by experiment, and may be connected in series with either cell wire. By the use of this compensating resistance the bridge current may be varied over a wide range (150 to 300 milliamperes) without changing the balance point of the slide wire K , if dry air is contained in both cell tubes. It is, of course, possible to dispense with this compensating coil, but its use simplifies the operation of the instrument. Inasmuch as industrial gases differ greatly in thermal conductivity, a set of shunts, c, d, and e, is provided for the slide wire K . By setting the proper shunt on the slide wire with a movable plug, the range of the instrument can be varied over wide limits. Further variation is possible by changing the bridge current within the limits of 150 and 300
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milliamperes. The lower the value of the shunt resistance and the higher the bridge current, the higher the sensitivity will be. Any gahranometer may be used which will be properly damped on the circuit. The one usually employed is a box-type reflecting instrument with a sensitivity of 25 microvolts per 1-mm. scale division, and an external critical d a m p ing resistance of 80 ohms. Naturally, if higher sensitivities are required a more sensitive galvanometer should be chosen. Measurement of Air-Gas Ratios
This instrument was first designed to determine the percentage of illuminating gas in air, for experimental work on gas heating devices. A sample of the unburned gas-air mixture is withdrawn from the burner just after the mixing device, and is passed into the cell X , through a calcium chloride drying tower. W h e n s u f f i c i e n t gas mixture has been passed through to sweeD out, . . Air-Gas Ratio the t;bes, the do, is Figure 4-Complete Apparatus stopped and the bridge is balanced. This gives the reading K , on the slide wire. Then dry air is passed through the cell tube and a reading KOis obtained. Finally, pure fuel gas (illuminating gas in this case) is passed through, and the reading K1 is obtained. Figure 6 shows a curve (1) of fuel gas concentration, in air, versus slide wire readings K . The curve is a calibration curve for the apparatus, and has been previously determined by passing known mixtures of fuel gas and air through the cell tube X and taking the slide wire readings. The value a t 110 v, A t o r
DC
T
t
Galv.
I I
Slidewire
Figure 5-Circuit
K Diagram
100 per cent fuel gas is the important point. Such curves ordinarily will be straight lines or, if not straight, the curvature will be slight. Kow, having the slide wire reading K , for the unknown mixture, reference to the curve (1) will give the percentage of fuel gas in the air directly, or if desired the air-gas ratio.
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 data 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-
