Improved Method of Determining Densities of Viscous Fluids with Babcock Bottles RICHARD S. CASS, JOH3 B. GREGORY, AND ERNEST LEVENS' Frederick S. Bacon Laboratories, Watertown, Mass. t>pes of pycnometers have been devised to measure (1, 4-7). Although they are witable for the purpose for which they are designed, they are difficult to manipulate when viscous fluids are involved owing to poor capillary flow, have poor precision due to nonreproducible seating of ground glass joints, or are time-consuming when determining coefficient of expansion because of the necessity of having to refill and reneigh the pycometer for each measuring temperature. The method described below provides precise and rapid testing of viscous fluids at different temperatures. The pycnometeis used ( 2 , 3) are Babcock milk test bottles (Cenco S o . 24340 or equivalent). These bottles have a wide base, a neck nith 0 02 ml. per graduation, and a volume of 1.6 ml. The over-all volume of the bottle is about 50 ml. The Babcock bottles are relatively easy to fill nith a pipet and can be loaded in an oven if fluids too viscous to floii at room temperature are encountered. These bottles are adapted to nonviscous as well as viscous fluids. Density-temperature data can be obtained over a Ride range of temperatures (130' F. for many fluids) without a sepalate weighing for each determination. Only initial (tare) and final weighings, as well as neck ieadings at each temperature, are necessary. AI
IC1 densities
Table I . Denqit! of a Fluid in Different Babcock BottlesU
Av. 1.9244 llaxilnurn d e r . f r o m mean +0.0005 Average dev. from mean 10.0002 Standard del-. from mean ~0.0001 a Viscosity of fluid equal t o approximately 400 cp. a t test temperature of
144.7' F.
Table 11. Density of Viscous Fluids in Different Bahcock Bottles Fluid No.
Bottle No.
14
3
1.9238 1,9242 1.9239
1.9408 1.9410 1.9408 1.9425 1.9427 1.9426
1 4244 1 92.52 1 9249 1.9267 1 9271 1.9269
1.9402 1.9402 1.9402
1.9241 1 9242 1 9242
1.9399 1.9399 1.9400 1 1.9400 64 3 1.9399 4 1.9400 a Viscosity a t 160° F. approximately 1500 cp. b Test temperature 160.1' F. C Viscosity at l6Oo F. approximately 2000 cp.
1.9242 1,9239 1.9239 1 ,9239 1.9236 1.9239
8 3 4 5
2c
3e
Calibrate the bottles by the standard method (1 ); the neck as well as the bulb must be calibrated. Determine the volume of the bulb a t three temperatures over at least a 100" F. range (the authors used loo", 140", and 180" F.) using Kational Bureau of Standards oil, Type S , or equivalent. Water may be used a t the lower temperatures. If the thermal expansion of the bulb I S not linear with temperature after a second set of determinations, discard the bottle (this has been encountered in only one bottle to date). The neck volume is independent of temperature within experimental error. To fill the bottles these laboratories use c i 50-ml. pipet in which a glass efflux tube 3 mm. in outside diameter replaces the standard efflux tube. The size of the efflux tube is not reduced a t the end. After filling, cool the bottles to below the test temperature, and carefully clean the neck of any adhering test fluid with a lintless tissue. If more than one test temperature is employed, use the lowest one first, so that drainage errors are eliminated. Make neck readings a t 10-minute intervals until three consecutive identical values are obtained. This assures thermal equilibrium These laboratories use an analytical balance having a sensitivity of 0.0001 gram and a constant-temperature water bath with a precision of &0.008" F. and an accuracy of 0.1" F.
Density, G. ,111. 160.2' F. 179.8' F. 1.9404a 1 ,9403 h 1.9404b
4
PROCEDURE
A formula indicating the Babcock bottle constants has been developed, so that when the density is calculated at a known temperature, only values of neck reading and fluid Reight are necessary:
Density, G '111
Bottle S o .
1
6 8 5
4a
6
a
1
3 4
Conclusions. For each set of triplicate determinations the maximum spread of values is C0.0002 gram per ml. ( 3 ~ 0 . 0 1 % ) ;a n y individual value may be considered t o have this precision.
any particular bottle. With care, a precision of *0.0002 gram per ml. (=kO.OlO/,)can be obtained with fluid viscosities of 1000'to 2000 cp. and temperatures of 160' to 180' F. (see Table 11). Densities obtained by the Babcock method with similar fluids have been checked with standard pycnometers with complete agreement in the third decimal place (1 part in 2000). The absolute accuracy is probably about *0.050/, because of the additional errors involved in calibration.
W
ACKNOWLEDGMENT
t
= density of fluid a t t o F., grams per ml. = true weight in vacuo of fluid in bottle, grams = volume of bulb a t 0' F. (extrapolated), ml. = temperature of fluid (same as temperature of constant-
A portion of this work was sponsored by the Instrumentation Laboratory at the Massachusetts Institute of Technology in connection with research for the Research Division and Weapons Components Division of Wright Air Development Center, U. S. Air Force.
IC
= temuerature coefficient of bulb as determined bv cali-
dt
=
V b
where dt
W Vb
temperature bath),
+ kt + n V 1
' F.
bration, ml. per ' F. V,,= volume of neck (temperature-independent within experimental error), ml. per division. n = Babcock bottle neck reading (estimated to tenths of a graduation)
LITERATURE CITED
(1) Am. SOC.Testing Materials, Philadelphia, "-4.S.T.M. Standards,"
Designation D 70-27.
These laboratories have determined fluid densities with a standard deviation of i ~ 0 . 0 0 0 1gram per ml. (=t0.005%) using different bottles (see Table I). Precision is slightly better for
(2)Ibid., D 872-46T. (3) Ibid., D 872-48. (4) Ibid., D 941-49. (5) Downing, V. F.. et al., A N A L . CAEM.,24,229, 230 (1952). (6) Lipkin, M.R., et al., Ibid., 21, 504-7 (1949). (7) Lipkin, RI. R.,et al., IND.ENQ.CHEM..ANAL. ED.,16, 55-8
1 Present addresa, American Potash a n d Chemical Co., Loa Angeles, Calif.
RECEIVED for review J u l y 30, 1952.
(1944).
1773
Accepted July 30, 1953.
