Thermostatic Bath for Low-Temperature Viscosity Determinations E. L. BALDESCHWIELER AND L. Z. WILCOX, Standard Oil Development Co., Linden, N. J .
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rent being controlled by means of a mercury thermoregulator connected to a vacuum tube relay. No description of the bath used for cooling the circulating alcohol was given. The work of the above investigators shows t h a t the determination of low-temperature viscosities is a fairly complicated problem. Such determinations are therefore not generally considered a part of the routine of petroleum inspection laboratories. However, special problems often require the use of viscosity data a t low temperatures and to meet this demand a setup capable of furnishing accurate data a t short notice was designed by the authors. This setup has been found very satisfactory and, for this reason, it should be of interest to other laboratories engaged in similar work.
HE determination of the viscosity of liquids a t low
temperatures presents a number of mechanical difficulties which cannot be overcome without the use of elaborate setups. The main sources of error are due to poor temperature control and also, if a pressure instrument is used, to difficulties in maintaining constant pressure. Since the viscosity of fluids increases very rapidly with decreasing temperature, the importance of proper control of temperature is evident in order to avoid large variations in results. Moreover, such close temperature control must be maintained for much longer periods of time, particularly when using viscometers of the capillary type. The viscosity of lubricating oils a t low temperatures has been determined by a number of authors, in particular Okochi and Majima (7), Schlenker (8), Tonomura ( I d ) , Tausz and Mellner (II), Ferry and Parks (d), Tanaka, Kobayasi, Tsukuda, and Ono (IO), FitzSimons (S), Ivanov and Gutzeit (6),Jordachescu (6), and Schwaiger (9). I n general either no data were furnished on the accuracy of the temperature control or such control was limited to *0.5" C., which is too wide a variation for precise measurements. The FitzSimons apparatus gave temperature variations not exceeding 0.01 " C. by circulating ethyl alcohol a t -60" C. in a copper coil inserted in a Dewar flask containing ethyl alcohol. The desired temperature was then obtained by heating the bath with an immersion electric heater, the cur-
Apparatus The apparatus shown in Figure 1 consists of three parts: cooling coil and bath, thermostatic bath, and viscometer and bath. The cooling coil, C, consis& of a copper coil immersed in a bath, B, of alcohol cooled to the desired tem erature by occasional additions of solid carbon dioxide. Coil t i s connected to the cooling coil, D, of a Hoeppler ultrathermostat, H (4), the liquid (a suitable alcohol-water mixture) being circulated by means of a small centrifugal pump, P.
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FIGURE 1. DIAGRAM OF APPARATUS 221
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Bath E is an unsilvered Dewar, of 10-liter capacity, covered with a grooved hard-rubber head surmounted by a brass plate held firmly by means of the rods and bolts, P. A tight joint is obtained by inserting a rubber gasket in the groove of the hardrubber head. The brass cover is provided with a tapered hole through which a Ubbelohde viscometer (IS) held by a rubber cork is inserted. The viscometer is calibrated in accordance with A. S. T. M. procedure ( I ) . Baths B and H , as well as all connecting lines, should be heavily insulated with cork in order to prevent moisture condensation. The Hoeppler falling-ball viscometer (4) can be substituted for bath E for temperatures above O", but cannot be used for temperatures much below 0", because of frost formation on the surace of the outer jacket. For this reason, a Dewar bath is more preferable. In carrying out a determination, bath B is filled with either alcohol or acetone (isopropyl alcohol being very convenient) ; and a suitable water-alcohol mixture is introduced through cock M into the cooling coil system as well as into baths H and E. The freezing point of the alcohol-water mixture must be a t least 20" C. below the desired viscosity temperature. The viscometer is then inserted in bath E, the thermostat is plugged in, and circulation pumps P and R are started. The alcohol in bath B is rapidly cooled by additions of solid carbon dioxide to the desired temperature. I n general it is necessary to maintain the coil temperature about 8" to lod C. lower than the temperature desired in bath E in order to obtain the best thermostatic control with the Hoeppler apparatus. This can be accomplished by regulating the addition of solid carbon dioxide so as to maintain the temperature of bath B about 10" lower than that of the coils. Still better rocedures consist of regulating the circulation rate by means o r a rheostat attached to the motor, or adjusting the pressure by means of stopcocks M and N . The temperatures of the incoming and outgoing fluids are read by means of thermometers 1'7 and Te-for example, if a temperature of -10" C. is desired in bath E, the coil temperature must be about - 18' to -20" C. and bath B about -30" C. Under the above conditions, the thermostat is capable of tem erature control within 10.03' C. in bath E as read with a Lee& & Northrup Type 8662 potentiometer.
The thermostat is generally suplied with a mercury regulator For lower temperatures the for temperatures down to -25" authors have replaced this mercury control with a Burling metallic thermostat which has been attached to the Hoeppler bath. With this thermostat temperatures as low as -52" C. have been maintained within *0.03" C. for hours without difficulty. The Burling thermostat used for this work was designed for temperatures of about -60" C.; it did not give suU,ch good control around -30" C., the variations being about k O . 1 . I n ordering this thermostat the temperature range must be specified for best results.
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Acknowledgment The authors wish t o express their appreciation t o E. M. Fry and W. J. Troeller of these laboratories for their valuable suggestions.
Literature Cited (1) Am. Soo. Testing Materials, "A. S. T. M. Standards on Petroleum Products and Lubricants," Report of Committee D-2, p. 314, 1937. (2) Ferry, J. D., and Parks, G. S., Physics, 6, 356 (1935). (3) FitzSimons, O., paper presented before the Division of Petroleum Chemistry, Pittsburgh meeting of American Chemical Society, 1936. (4) Hoeppler, F., Brennstof-Chem., 14, 234 (1933); 2. tech. Physik, 14, 165 (1933). (5) Ivanov, K. I., and Gutzeit, A. M., Neftyanoe Khozl. (U. S . 9. R,), 18, No. 6 , 32 (1937). (6) Jordachescu, M., Ann. combustibles liquides, 12, 511, 735 (1937). (7) Okochi, M., and Majima, J . Chem. SOC.,74, 463 (1923). (8) Schlenker, E., Brennstof-Chem., 12, 25 (1931). (9) Schwaiger, Petroleum Z., 34, 23 (1938); Motorenbetrieb Maschinen-Schmierung, l l , No. 6, 8 (1933). (10) Tanaka, Y., Kobayasi, R., Taukuda, T., and Ono, T. J., SOC. Chem. Id., Japan Suppl., 39, 172B (1936). (11) Tausz, J., and MeIlner, H., Petroleum Z.,28, No. 45, 1 (1932). (12) Tonomura, T., Bull. Chem. SOC.Japan, 6 , 124 (1931). (13) Ubbelohde, L., J.Inst. Petroleum Tech., 19,376 (1933).
A High-Performance Electronic Relay ROLAND C. HAWES, 672 South Westlake Ave., Los Angeles, Calif.
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HE relay described in this paper was designed primarily for use with a mercury thermoregulator for controlling the temperature of a water bath. The requisites for this service-small control contact current to prevent deterioration of the contacts, low control contact voltage to prevent sparking and insulation breakdown (which is especially desirable because of the high humidities often encountered), simplicity, and low cost-are met t o an unusual degree. To obtain the lowest contact voltages possible in a design using one receiving type tube and but a single sturdy magnetic relay, the circuit, Figure 1, takes advantage of characteristics
of one of the new higher transconductance, "beam" t y p e tubes and utilizes grid rectification of the control circuit voltage. It requires no source of power other than the usual 110volt single-phase line. It is especially useful to prevent chatter of the magnetic relay under conditions of vibration because of the fact that condenser CI is relatively slowly charged or discharged.
Circuit A of Figure 1 is connected for use with a mercury thermoregulator (controlled circuit open when controlling circuit is closed). To connect it for use wlth a bimetal regulator, it is necessary merely to rewire the grid circuit leads as at B. To place the relay in operation, the strap connected to the tube cathode should be placed a t about the center, and the other movable contact a t the ground end of R,. To obtain minimal voltage across the contact points, the cathode strap is first adjusted so that the relay will just open when the control terminals are shorted (or opened, if the circuit is arranged as in B ) , then the other strap is (. moved towards it until the relay just closes, when the control terminals are opened. Too fine an adjustment should not be attempted, since some allowance for line voltage flucA B tuation is necessary. When FIGURE 1. DIAGRAM OF CIRCUIT properly adjusted, the root Tube 25L6 or 25L6-G. Relay, 3000-ohm 20-milliampere ooil, Leach No. 1201 mean square values of voltage Rz. 50 ohms 10 watts; I R C PBA, c1. 8-microfarad, 150-volt electrolytic, and current across the control with ex&a atrap Cornel1 Dubilier BR No. 875 points are approximately 8 Ra, Rs. 0.1 megohm 1 watt. I R C BT-I Ca . 0.1 microfarad, paper volts and 0.1 milliampere. Ra. 1.0 megohm, 1 h t ; IRC BT-1 RI. 250 ohms, 50 watts; IRC P E
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