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Standard substances for the calibration of viscometers
NOTES
FROM
THE
U. S. B U R E A U
OF STANDARDS.*
STANDARD sUBSTANCES FOR THE CALIBRATION OF VISCOMETERS. 1 Eugene C. Bingham and Richard F. Jackson.
[ABs'rkacT.j FOR the purpose of the calibration of viscometers there is a need for one or more liquids of viscosity greater-than water which can b e easily obtained in pure condition and whose viscosity is known with a considerable degree of certainty. The substances selected, besides water, were mixtures of ethyl alcohol and water, and sucrose and water. Previous work upon water and alcohol was adequate and consequently the experiments were confined to the sucrose and water. The sucrose was purified by repeated recrystallization from water solution and contained residual impurities of the order of one-thousandth of a per cent. The solutions used in the measurements were analyzed by determination of density and by polariscopic test. The viscometer used in the investigation consisted essentially of a U-tube fitted with a capillary on one limb surmounted by a bull) with constrictions which could be used to measure the volume of liquid. A bulb of similar size and shape was sealed on the other limb. The viscometer was connected to a manometer and pressure apparatus for the application of pressure. From the observations the viscosity was calculated by the usual formula rr = C p t
C' p / t
in which p is applied pressure, o density of liquid, t time of flow, C and C' constants abbreviated from the complete viscosity fornmla. C' was found by direct calculation, C by measuring the time of flow of pure water at 2o ° C. and substituting its viscosity o.omo5. The viscosity was measured at a variety of gpplied' pressures. To obtain the true effective pressure, the height of liquid in the manometer is corrected for air buoyancy, column of connecting *-Communicated bx; the Director. V'OL. 183, NO. lO94--17.
~Scientific Paper No. 298: 229
230
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
air and hydrostatic head of the liquid undergoing measurement. In order to be certain that the drainage of solution was complete the time of flow required to discharge and to fill the bulb was measured. Furthermore, viscosity was found to be independent of applied pressure. To test calculations and corrections the viscosities of water were measured, using a considerable range of pressures. The value was found to be constant. In order to avoid the arbitrary scales of commercial viscometers and the~ inconvenient magnitudes of the absolute units, we suggest the use of the " centipoise" as a unit of viscosity. This is one-hundredth part of the C. G. S. absolute unit. The centipoise is almost exactly the viscosity of water at 20 ° C. (1.oo5) and, hence, is at the same time the specific viscosity of any substance referred to water at very nearly 20 ° C. The viscosities of water have been determined by several investigators. The existing data has been reviewed in order to correct it so far as possible according to our present knowledge. The mean values expressed as fluidities may be expressed by the formula : 4,=2.I482 { ( t - 8 . 4 3 5 ) + ~ / ~ 7 8 . 4 + ( t - 8 . 4 3 5 ) 2 } - 1 2 o in which 4 is fluidity and t centigrade temperature. Mixtures of ethyl alcohol and water may be used as standards. Their fluidities expressed as functions of temperature and weight and volume percentage of alcohol accompany the complete article. The viscosities of a 3 9 . 9 9 per cent. sucrose solution were measured at temperatures varying from o ° C. to 95 ° C. The observed values corresponded to the formula : I438.6 + 38.24. t = o . 5 9 7 (¢,÷2o) - ÷+2o
Inasmuch as some discrepancy was found to exist between this and former values the experiment was repeated and practically the same values were obtained. The measurements were then made on 20.007 per cent. and 59.96 per cent. sucrose solutions. The fluidities at the latter concentration corresponded to the formula: ~2,~.2 t = I . 4 7 2 ( ~ ' + 5 ) - ~+5
.j. 5 8 . 6 2 , .
The values found in the present investigation indicated a higher viscosity than those of previous investigators.
FROM
THE
U. S. B U R E A U
OF STANDARDS.*
STANDARD sUBSTANCES FOR THE CALIBRATION OF VISCOMETERS. 1 Eugene C. Bingham and Richard F. Jackson.
[ABs'rkacT.j FOR the purpose of the calibration of viscometers there is a need for one or more liquids of viscosity greater-than water which can b e easily obtained in pure condition and whose viscosity is known with a considerable degree of certainty. The substances selected, besides water, were mixtures of ethyl alcohol and water, and sucrose and water. Previous work upon water and alcohol was adequate and consequently the experiments were confined to the sucrose and water. The sucrose was purified by repeated recrystallization from water solution and contained residual impurities of the order of one-thousandth of a per cent. The solutions used in the measurements were analyzed by determination of density and by polariscopic test. The viscometer used in the investigation consisted essentially of a U-tube fitted with a capillary on one limb surmounted by a bull) with constrictions which could be used to measure the volume of liquid. A bulb of similar size and shape was sealed on the other limb. The viscometer was connected to a manometer and pressure apparatus for the application of pressure. From the observations the viscosity was calculated by the usual formula rr = C p t
C' p / t
in which p is applied pressure, o density of liquid, t time of flow, C and C' constants abbreviated from the complete viscosity fornmla. C' was found by direct calculation, C by measuring the time of flow of pure water at 2o ° C. and substituting its viscosity o.omo5. The viscosity was measured at a variety of gpplied' pressures. To obtain the true effective pressure, the height of liquid in the manometer is corrected for air buoyancy, column of connecting *-Communicated bx; the Director. V'OL. 183, NO. lO94--17.
~Scientific Paper No. 298: 229
230
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
air and hydrostatic head of the liquid undergoing measurement. In order to be certain that the drainage of solution was complete the time of flow required to discharge and to fill the bulb was measured. Furthermore, viscosity was found to be independent of applied pressure. To test calculations and corrections the viscosities of water were measured, using a considerable range of pressures. The value was found to be constant. In order to avoid the arbitrary scales of commercial viscometers and the~ inconvenient magnitudes of the absolute units, we suggest the use of the " centipoise" as a unit of viscosity. This is one-hundredth part of the C. G. S. absolute unit. The centipoise is almost exactly the viscosity of water at 20 ° C. (1.oo5) and, hence, is at the same time the specific viscosity of any substance referred to water at very nearly 20 ° C. The viscosities of water have been determined by several investigators. The existing data has been reviewed in order to correct it so far as possible according to our present knowledge. The mean values expressed as fluidities may be expressed by the formula : 4,=2.I482 { ( t - 8 . 4 3 5 ) + ~ / ~ 7 8 . 4 + ( t - 8 . 4 3 5 ) 2 } - 1 2 o in which 4 is fluidity and t centigrade temperature. Mixtures of ethyl alcohol and water may be used as standards. Their fluidities expressed as functions of temperature and weight and volume percentage of alcohol accompany the complete article. The viscosities of a 3 9 . 9 9 per cent. sucrose solution were measured at temperatures varying from o ° C. to 95 ° C. The observed values corresponded to the formula : I438.6 + 38.24. t = o . 5 9 7 (¢,÷2o) - ÷+2o
Inasmuch as some discrepancy was found to exist between this and former values the experiment was repeated and practically the same values were obtained. The measurements were then made on 20.007 per cent. and 59.96 per cent. sucrose solutions. The fluidities at the latter concentration corresponded to the formula: ~2,~.2 t = I . 4 7 2 ( ~ ' + 5 ) - ~+5
.j. 5 8 . 6 2 , .
The values found in the present investigation indicated a higher viscosity than those of previous investigators.