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THE JOURNAL OF INDUSTRIAL AND EhTGIiVEERING CHEMISTRY
recently been standardized by the Bureau of Standards and was read with a microscope. Considerable attention was given to the method of reading the pressure. Owing to the fact that the capillary of the Yo. 1 viscosimeter was quite small, it was necessary to use pressures as high as 85 cm. of mercury in order to obtain a reasonable time of flow. It was, therefore, decided to use a mercury manometer and to read this with a cathetometer. It was believed possible to secure in this manner quite as high a degree of accuracy as would have been secured had the ordinary water manometer with the steel tape been used. When the time of flow exceeded an hour, the writers found considerable difficulty in securing an accurate record of the time. Although the ordinary stop watch may be of sufficient accuracy where the time does not exceed 5 min., it appears to show large errors when times of an hour or more have to be measured. The ordinary stop watch is quite difficult to regulate and even more difficult to keep in adjustment, but the writers finally found a watch that could be checked within one second in an hour against an astronomical clock. It would appear that there is quite a field of usefulness for a piece of apparatus, not too expensive, which would give accurate time intervals up to an hour. In connection with the standardization of the apparatus, the writers found the great need, which has been spoken of by other observers, for a pure and reproducible material that would have a viscosity at ordinary temperatures of 40 to 50 centipoises. The No. 1 viscosimeter was standardized with water and 50 per cent ethyl alcohol. The No. 2 viscosimeter was standardized with 50 per cent ethyl alcohol, 40 per cent sucrose, and GO per cent sucrose. Bureau of Standards sucrose was used in making up the sucrose solutions. RESULTS
A very highly refined white medicinal oil gave an absolute viscosity a t 37-78" C. of 40.3G centipoises. When this material was allowed to stand in the viscosimeter for 24 hrs., the viscosity decreased by 0.54 per cent. On retesting this sample 2 mo. later, the viscosity had decreased by 0.43 per cent. A petroleum oil of reddish color which had been refined by filtration gave a viscosity of 38.35 centipoises. On standing 24 hrs. in the viscosimeter the viscosity increased by 0.42 per cent. This sample after standing 5 wks. in a tin can had increased by 0.42 per cent. The greatest number of observations were made on this sample. They showed a gradual increase in viscosity with time, the obfierved figures being for the fresh sample as given above, 38.35, then 38.36, 38.41, and the last observation 5 wks. later, 38-46. In order to get some further information regarding the possible sign and extent of this change on standing, two samples of petroleum oil furnished by Dr. Delbridge of the Atlantic Refining Company were examined. It is understood that one of these oils was refined by filtration, while the other was not. Samples of both were exposed on the roof in white glass bottles for a week. The filtered oil showed no change in the viscosity between the sample exposed to the light and the sample kept in the dark, while the unfiltered oil showed an increase of 1 per cent in the sample that had been exposed to the light. A sample of castor oil showed an increase of 0.33 per cent on standing in the viscosimeter for 24 hrs., while a sample of lard oil showed a decrease of 0.3 per cent on standing in the viscosimeter for 24 hrs. The writers have not as yet formulated any theory of the cause of these changes; it may be pointed out, however, that
Vol. 14, No. 8
the fact that the results were checked with viscosimeters of both wide and narrow bore apparently excludes the formation of films of material dimensions on the inside surface of the capillary, thus changing the bore. It may be, however, that an adsorbed film of molecular dimensions is formed in the capillary and that this adsorbed film has a different viscosity from that of the oil. It is the intention of the writers to retest some of these samples for a number of months in order to determine, if possible, whether they will come into equilibrium or whether the change will be continuous. This study should be of some importance as affecting the usefulness of samples that are to be retained for long periods as standards of viscosity.
The Drainage Error in the Bingham Viscosimeter By Winslow H. Herschel BUREAU of STANDARDS, WASHINGTON, D. C.
[Discussion of preceding paper]
It is well known that the volume discharged from a flask is less than the volume it will receive, even when the calibration is made with water, and this is even more the case when a more viscous liquid is used. It follows that the discharge with oil is less than the discharge with water. 4994
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The Bingham viscosimeter is so arranged that the bulb becomes wet in fixing the working volume, so that it is difficult to observe or measure the drainage error. Comparisons of various viscometers led to the conclusion that the error was serious enough to require investigation, and a special instrument was made up with a bulb similar in shape and size to that of the Bingham instrument, and so arranged that the drainage error could be measured by calibration with liquids of various viscosities. On the diagram, which shows the results to date, the numbers on points give correction factors by which the constant C of the Bingham viscosimeter, obtained by calibration with water, must be divided to obtain the value to be used in obtaining the viscosity of liquids having a higher viscosity than that of the calibrating liquid. The diagram may also be used to determine the time of flow necessary to render the drainage error negligible.
In the Annual Report of the American Metric Associat;on recently issued, engineers, business men, and manufacturers who favor the adoption of the metric system in the United States are quoted at length, and the story of the extension of its use during 1921 is told. The use of the metric system is now obligatory in 46 countries.
