SEPTEMBER 15, 1940
ANALYTICAL EDITION
nections) in addition to the insertion of the current limiting resistor, R-10, and the voltage-regulator tube VR105. The socket connections for the latter tube are indicated in Figure 4. Since the 25Z6 rectifier rcquires greater heater power than the 6H6, the value of the line cord resistor, R-2, must be reduced to 250 ohms as shown. Connections X , 2,F-2, and F-1 are made at the points indicated in Figure 2 . The addition of this voltage-regulation feature will allow instantaneous alternating current line voltage variations of 15 volts without causing any perceptible change in the operating shadow of the magic eye. If 110-volt direct current is used to operate the titrimeter, the voltage regulator becomes inoperative. Grid Current When alternating current is applied to the plate of the 6F5 amplifier, a small amount of current will flow through the titration cell. This current will vary from a maximum of l l to a minimum of 4 microamperes, depending upon the position of the sensitivity control. Since the sensitivity is rarely changed during a titration, this current may fortunately be used as polarizing current for a monometallic platinumplatinum electrode system. If very small platinum electrodes are to be used, it may be necessary to reduce this polarization current to 2 to 5 microamperes by inserting resistance R-7 in series with the titration cell. For use with cells requiring a minimum of current drain, the rectified titrimeter must be employed. The grid current of this circuit is governed somewhat by the selection of vacuum tubes as well as the sensitivity setting and the applied e. m. f. A t maximum sensitivity and with zero applied e. m. f. the greatest amount of current found was 0.07 microampere. A decrease in sensitivity as well as a n increase in negative potential applied to the grid of the 6F5 produces a marked de-
539
crease in grid current. Thus, with 50 per cent of full sensitivity and a n applied e. m. f. of 0.2 volt, the grid current is decreased to 3 x 1O-IO ampere. For all practical purposes this minute current, will not affect even the most sensitive of titration cells. A polarization current of between 3 and 6 microamperes, depending again upon the sensitivity control, may be obtained from the rectified titrimeter for use with the polarized monometallic platinum-platinum electrode system. Since the sensitivity of the titrimeter is markedly decreased by the insertion of a high resistance in series with the externally applied e. m. f., the use of high-resistance electrodes such as the glass electrode will lead t o discouraging results. Furthermore, since both of the units described are of the t’ransformerless alternating-direct current type, caution must be exercised to prevent any part of the circuit or external electrode connections from becoming grounded. The electrode cables should be well insulated and care should be exercised that no part of the electrode system becomes grounded through the electrode holder and titration stand. As a n added precaution to the operat’or, the titration stand which holds the buret and stirring mot’ormay be grounded to a convenient water pipe. Literature Cited (1) (2) (3) (4)
(5) (6) (7) (8)
Eppley and Vosburgh, J . Am. Chem. Soc., 44, 2148 (1922). Garman and Dros, IND. ESG. CHEM.,Anal. Ed., 7, 341 (1935). Ibid., 11, 398 (1939). Goode, K. H., J . Am. Chem. SOC.,44, 26 (1922). Ibid., 47,2483 (1925). Rescorla, Camahan, and Fenske, IND.ENQ.CHEM.,Anal. Ed., 9, 505 (1937). Smith, G. F., and Sullivan, V. R., “Electron Beam Sectrometer”, G. Frederick Smith Chemical Co., 1936. Willard and Hager. ISD. ESG.CHEM..Anal. Ed.. 8, 144 (1936).
A Portable Aspirator Pump ROBERT C. HOCKETT Massachusetts Institute of Technology, Cambridge, Mass.
T
HE distillations under reduced pressure that are carried
out in most research laboratories fall generally into two types, (1) distillations of compounds to purify them under relatively mild conditions and (2) removal of solvents rapidly and a t relatively low temperatures. The pumps suitable for these distinct purposes are of quite different specifications. Mechanical and mercury diffusion pumps are well adapted for the vacuum distillations of organic liquids, since high vacua are often desirable and trapping out vapors presents a relatively easy problem, simply because the trapped substances are definitely minor constituents of the mixtures submitted to such treatment. On the other hand, where the problem is that of removing solvents in gallon quantities from nonvolatile materials, high vacua are rarely necessary, and the trapping of vapors so that not even traces will enter the pump becomes exceedingly difficult. I n such cases a n aspirator pump when operating a t maximum efficiency is almost ideal for the purpose, since no precautions need be taken against entrance of vapors into the aspirator where they are rapidly diluted with m-ater. The defects of the aspirator are due rather to the insufficient or fluctuating water pressures frequently encountered in laboratories, especially those above the ground floor. I n addition, the consumption of water may rise to very high figures.
The apparatus illustrated in the accompanying photograph
was designed to avoid these difficulties and also to confer the ad-
vantage of niobility upon the apparatus. -4 water pump (that sold by Sears and Roebuck, KO. 42 EM 2955, is of this type) designed primarily for summer camps and small cottages is used to drive water from a reservoir through an aspirator and back into the reservoir. The pump, which is of the piston type and operated by an electric motor, draws water from an intake and forces it into a cast-iron bulb against an air cushion which in turn throws o f f a pressure switch when 40 pounds is reached, thus cutting off the motor. As long as the escape of water is prevented the motor
INDUSTRIAL AND ENGINEERING CHEMISTRY
540
remains stationary. On opening the escape valve, water flows out to a minimum pressure of 25 pounds, at which point the pressure switch again starts the motor. The author mounted this pump upon a centrifuge carriage equipped with large castors. (The centrifuge truck sold by the Central Scientific Company, No. 11,681, meets these specifications. A satisfactory truck could easily be improvised using wooden boards, pipe, and castors.) A 6-inch section of copper pipe connects the pump outlet through a gate valve t o an ordinary aspirator from which water flows through a copper tube into a 10gallon wooden keg suspended underneath the carriage and half filled with water. The pump inlet is attached to a section of garden hose which dips to the bottom of the same reservoir. The air inlet of the aspirator is threaded into a brass tee, one arm of which is attached to the system to be evacuated while the other carries a vacuum gage. (The Central Scientific Company’s vacuum gage S o . 94,030 is very suitable.) To operate, it is only necessary to plug in tlie electrical connection and open the gate valve. I n practice, the author has
VOL. 12, NO. 9
found that when the gate is wide open, the motor runs almost continuously. Operating between pressures of 25 and 40 pounds the efficiency of the aspirator is maintained a t a maximum and without fluctuations. Such a pump will evacuate a system of 2-quart capacity to the vapor pressure of water in about 2 minutes. By slight modifications it might be possible t o obtain lower pressures by using ice mater. A plug near the bottom of the reservoir permits draining out the contents, which are conveniently replenished through the intake hose. Since the water is recirculated, the removal of only neutral solvents is recommended, and frequent changes of reservoir liquid are desirable. Though planned primarily for concentrating aqueous solutions, the pump has handled methanol, ethanol, chloroform, and the Cellosolves very satisfactorily. I t s use has very markedly speeded u p thk concentration of solutions in this laboratory.
Saybolt One Fifteen Viscometer J
E. W. DEAN, E. L. RUH, AND R. W. WALKER, Standard Oil Development Co., New York, Y. Y .
T
HE Saybolt viscometer wab devised in its original form by George M. Saybolt in 1885 (6). After passing through several stages of development the so-called Universal type was standardized by the U. S. Bureau of Standards (6) about 1917, and the Furol type was adopted by the United States Shipping Board (4) for testing its purchases of fuel oil during 1920. Both instruments were subsequently adopted as standards by the American Society for Testing Xaterials, the American Petroleum Institute, and the American Standards Association. The Saybolt Furol instrument is used chiefly for testing “heavy” fuel oils. The Universal, mhich gives values approximately ten times those of the Furol, is employed chiefly for lubricating oils.
Purpose of Saybolt One Fifteen Viscometer Modern developments in the production and utilization of lubricating oils have created a need for a higher degree of precision in the determination of viscosity than can be attained with the Saybolt Universal viscometer. The A. S. T. M. has standardized apparatus and procedure for the convenient and accurate determination of kinematic viscosity (3) and has established official tables ( 1 ) for the conversion of these values to the familiar Saybolt Universal scale, These developments, however, do not fully meet the needs of certain laboratories where conditions are not favorable for the use of long-capillary glass instruments. The Saybolt Universal viscometer, if properly operated, is a n instrument of considerable precision. A. S. T. M. Method D8&38 indicates maximum errors not exceeding 0.5 per cent for tests performed under optimum conditions. This degree of accuracy, however, is somewhat difficult to attain with products of low viscosity, as illustrated by the fact that it represents only 0.2 second for a n oil of 40 seconds outflow time. Errors in the measurement of time can often account for variations of this magnitude. Furthermore, the relationship between the Saybolt Universal and kinematic scales is such that this 0.2 second is actually equivalent to a difference of about 1.5 per cent in kinematic viscosity. The Saybolt One Fifteen viscometer, described in more detail below, is identical with the Universal except that the diameter of the outflow tube is smaller. This increases the efflux time and accomplishes the double purpose of improving the accuracy of determinations in the low range and reducing the ratio between differences in terms of the Saybolt out-
f l o n time and kinematic viscosity. As a conservative e d mate it may be stated that the Saybolt One Fifteen instrument gives as good accuracy with a 4.0-centistoke oil as the Universal does with a 15.0-centistoke oil. The approximate Saybolt Universal equivalents of 4.0 and 15.0 centistokes are 40 and 77 seconds, respectively.
Development Experience with the Furol viscometer has demonstrated the possibility of adapting the Saybolt type of instrument to products that cannot be tested conveniently in the Universal. The Furol and Universal are identical except as regards diameters of the outlet tubes, and the outflow time of the former is about one tenth of that of the latter. It was thought that another instrument might be developed which had an outflow time about ten times that of the Universal. An outlet tube was made with the diameter calculated to give the desired rate of flow and a t the same time several othera were fabricated which had progressively larger orifices. These were attached to available tubes and tried out in actual tests on several low viscosity oils. The combined experience of the instrument maker who fabricated the outlet tubes and the laboratory operators who used the instruments indicated that an orifice diameter of about 1.15 mm. and a theoretical efflux time ratio of 5.5 was preferable to the approximate orifice diameter of 0.99 mm. which gave a ratio of ten to one as compared with the Universal. After reaching a decision regarding the general characteristics of the new instrument, a number of complete tubes Ivere fabricated and placed in service in laboratories of companies with which the authors are associated. Satisfactory experience has been reported throughout a period in excess of a year. After casual consideration of several possible names for the new instrument, i t n-as decided to designate it in terms of the approximate metric diameter of the outlet tube.
Calibration After some initial experience with a tentative calibration curve developed by direct comparison of Saybolt Universal and Saybolt One Fifteen instruments, it was decided that the latter should preferably be calibrated in terms of kinematic viscosity. A number of suitable oils were obtained and tested. The results obtained are shown in Table I.
