Determination of Viscosity of Small Samples
of Oil from Oil-Impregnated Paper Method and Apparatus H. F. SCHNEIDER, JR.,
AND
T. A. MCCONNELL, Detroit Edison Company, Detroit, Mich.
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T HAS been observed in the e x a m i n a t i o n of the i n s u l a t i o n of p a p e r - a n d oilinsulated highvoltage cables taken from service that the viscosity of the oil in the insulation v a r i e s markedly from the center to the outside of the cable. This condition was also o b s e r v e d in cables s u b j e c t e d to laboratory treatments simulating service conditions. In order to interpret theee c h a n g e s , it was necessary t o evaluFIGURE1. PHOTOGRAPH OF APPARATUS ate them numerically. This was difficult because only 0.5 to 2 ml. of the oil were available for test. In the course of the investigations, several methods for determining the viscosity of small amounts of oil were tried. The first was the Ostwald method, which had to be abandoned because of the time involved in making the determination and the difficulty encountered in introducing the viscous oil into the apparatus. The second, which involved the use of a calibrated pipet, also proved unsatisfactory because of the difficulty of making suitable orifices adaptable over the wide range of the various cable oils tested. A method using the ball and inclined tube type of viscometer has been found to eliminate these difficulties. Although the apparatus and method described herein may have numerous shortcomings, they have been used successfully. They are applicable to viscosity determinations on small samples, are fairly rapid, and lend themselves to ease of manipulation.
water jacket by means of rubber stoppers in such a manner that the capillary tube protrudes slightly through each end of the water jacket. By placing the concentric or "static" jacket around the capillary and then placing the jacketed tube in the water bath, a more nearly constant temperature could be obtained. The jacket also served to keep the tube nearer the desired temperature during the introduction of the oil into the tube. The temperature of the water surrounding the capillary tube is obtained by means of an A. s. T. M. viscometer thermometer (0.11' C., 0.2' F. graduations) inserted in the upper rubber stopper. During the determinations this part of the apparatus is immersed in a thermostatically controlled water bath. The capillary tube is scaled each 4 cm., so that the viscosity may be measured by the time necessary for the ball to pass between any two or more divisions, depending on the viscosity of the oil and the amount of oil available.
Manipulation of Apparatus The manner of determining viscosity values is as follows: With the capillary tube, B, open at both ends, the oil to be tested is poured slowly into it, care being taken to entrap no air. Because of the high viscosity of the oil it will not flow quickly into and through the tube, so that the lower stopper can be removed. When the tube is completely filled or when all the oil available has been added, a small cork is inserted into the lower end of the tube. The jacketed capillarv tube assemblv is then Dlaced mldA in "a transparent walled water bath, maintained at a desired temperature (37.8" C., 100" F., in the case of the determinations mentioned herein), in such a manner that the capillary tube is held at an angle of 60" from horizontal. The ball, which has been brought t o the temperature of the oil, is quickly introduced through the top end of the capillary tube. The measure of the viscosity is determined from the length of time in seconds required for the ball to travel between selected graduations on the tube. Viscosity values are converted t o the terms of a standard viscosity scale by means of factors obtained during the calibration of the instrument using oils of known viscosity. In observing the position of the ball care should be taken that the eye is always in the same horizontal lane with the ball and at right angis with the vertical Dlane of the tube, so as t o avoid parallax. FIGURE2. DIAUsing a ball weighing 0.0548 gram GRAM OF ROLLINGBALLVISCOMETER and with a diameter of 0.237 cm. (0.0935 inch) and times of 8 to 300 A . Thermometer, seconds for a travel of 90 mm., it was A. S. T. M. B . Capillary tube found that the range of viscosities CI,CI. Rubber 8topwhich could be covered was about per6 0.70 to 25 poise, which, for the oils D. Water jacket E. Steel ball under consideration, is equivalent to h,Fa,Fa, Fd. Scale about 300 to 10,000 seconds, Saybolt marks Universal. U. Cork
I
Description of Apparatus The essential parts of the apparatus which is shown in Figures 1 and 2 consist of a capillary tube of approximately 2-ml. capacity for holding the oil to be tested and a small steel ball, the diameter of which is approximately one-half that of the capillary, During the development of the apparatus, it was found that when the capillary tube was placed directly in the thermostatically controlled water bath good checks could not be obtained. This was attributed to the fact that the bimetallic temperature-control mechanism which was readily available at that time was not sufficiently sensitive to control the temperature more closely than 0.28' C. (0.5' F.). The tube is held in position in a concentric glass 28
JANUARY 15, 1936
AKALYTICAL EDITION
Calibration of Apparatus As it has been observed that oils extracted from aged cable sometimes exhibit viscosity values which vary over a wide range, it has been found necessary to the apparatus using several oils of known viscosity over a comparable range. The calibration consisted of a series of runs with the ball and
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inclined tube viscometer using oils of known viscosities, The conversion factors obtained from these data are used in the calculation of the viscosity of the test samples, This work forms a part of a general research program on the deterioration of high-tension underground cable being undertaken by The Detroit Edison Company.
R~~~~~~~~~~~l29, 1935.
Determination of Water in Glvcerol J C. P. SPAETH AND G. F. HUTCHISON, E. 1. du Pont de Nemours & Co., Inc., Gibbstown, N. J.
I
F WATER is the only impurity in glycerol, it can be determined by specific gravity and reference to the and snoddy (2)tables Of mercial glycerol contains other impurities which affect the specific gravity, so that an accurate value for water cannot be obtained in this way, A knowledge of the true water in the content is often required-for industry t o compare nitroglycerin yields on the basis of dry glyceroi. Also, a direct determination is necessary in the complete analysis of crude glycerol. The international committee which adopted standard methods of glycerol analysis in 1910 (7) did not specify a method for the determination of water, indicating the unsatisfactory status of the methods available a t that time. Various methods depending on the measurement of physical properties have been described. Schmidt and Jones (10) and Kameyama and Semba (6) measured conductivity of electrolytes dissolved in glycerol. Grun and Wirth (3) used the determination of boiling point as an indication of water content. Hoyt (4) gave data on refractive index of glycerol containing various percentages of water. It is obvious that all these methods have the common defect of being accurate only for solutions of pure glycerol and water. Berth (1) used boiling tetrachloroethane to remove water from glycerol, condensing the vapors and collecting the water in a graduated tube. Hoyt and Clark (6) used toluene for the same purpose. Lawrie (8) mentioned the use of calcium carbide to liberate acetylene equivalent to the water present. H e also gave in detail the method of Rojahn (9) as modified by this laboratory. The original Rojahn method consisted of distributing about 1 gram of the sample of glycerol on ignited asbestos in a special weighing bottle and exposing it to phosphorus pentoxide in a desiccator evacuated to 10 to 15 mm. After 12 hours under these conditions, the loss in weight was calculated as per cent moisture. The modifications developed here consisted of an improvement in design of the weighing bottle, substitution of fine glass wool for asbestos, and extension of the time of desiccation to 24 hours. The modified Rojahn method has been used for a number of years as a standard procedure, but has not been entirely satisfactory. Duplicate determinations under the same conditions usually showed good agreement, but often did not agree with determinations by other laboratories on portions of the same sample. I n some cases, an experienced analyst was unable to check his previous determination a t a later date. Therefore, a further investigation was made with the object of learning the cause of these variations.
Preparation of Pure Glycerol Dynamite glycerol was refluxed with a large volume of toluene for 16 hours, collecting the water in a Bidwell-Sterling type of moisture-receiving tube. A considerable amount of the water was removed in this way. The toluene was separated from the
glycerol in a separatory funnel, and the glycerol placed in a 3liter distillation flask having a 25-cm. (10-inch) unpacked fractionating neck. It was then distilled slowly at about 5 mm. pressure and collected in a receiver which permitted fractionation without interrupting the distillation. The first 25 per cent of the distillate and a residue of about 15 per cent were discarded. Only the middle cut was retained. This distillation was repeated twice and a final middle cut was collected, without exposure to the air, in stoppered sample bottles, which were sealed with paraffin until used. The determination of the specific gravity offers a convenient and reliable method for establishing the water content of pure glycerol ( 2 ) . This method is recognized by the Committee on Glycerol Analysis and therefore has official status. Using it, the glycerol prepared as described above contained from 0.01 to 0.13 per cent of water. Considering the rapidity with which anhydrous glycerol absorbs moisture from the atmosphere and the necessary exposure in making a specific gravity determination, the purity and substantial freedom from water of the stock glycerol are well established. In order to avoid absorption of moisture from the atmosphere, it was important that a technic for handling this essentially anhydrous glycerol should be developed. The following method was used : The specific gravity was first determined in the usual manner in a Walker-type pycnometer. Upon completion, a one-hole rubber stopper was slipped around the outside of the neck of the pycnometer in an inverted position-that is, the large diameter of the stopper faced down. The capillary tube was now removed and the pycnometer quickly inverted over the mouth of a dry, tared Erlenmeyer flask in which the inverted stopper fitted. As soon as the glyceroi had been transferred, the pycnometer was removed and the flask carefully stoppered. Water and other impurities could now be added and their proportion determined by weight. The water found by the specific gravity determination on the purified glycerol was always included in the “calculated” water content of the sample. In order t o remove samples for analysis, a Lunge pipet or a shortened 5-ml. pipet was used. In either case the pipet was introduced into the flask containing the glycerol through a rubber stopper, and filled by compressing a rubber suction bulb. In this way the glycerol was exposed to the atmosphere for a minimum of time, and no difficulty was experienced from this source.
Modified Rojahn Method Portions of the specially purified glycerol, the water content of which had been established by specific gravity determinations, were made up to contain various percentages of water, such as are normally found in dynamite glycerol and crude glycerol. These were analyzed by the modified Rojahn method, as shown in Table I, which also includes similar determinations made in the presence of trimethylene glycol, a common impurity which is more volatile than glycerol. The trimethylene glycol was prepared by distilling Eastman’s practical grade a t atmospheric pressure and collecting the fraction boiling a t 212.6’ to 214.5’ C. This portion was redistilled once. It then contained 0.29 per cent of water (de-
