APPENDIX C
TECHNICAL VISCOMETERS
Instruments very different from those employed in scientific ]
work are much in vogue both in this country and abroad for
industrial purposes, particularly in the oil industry. Thus we
have the Engler Viskosimeter in Germany, the Redwood Vis- ff^
cometer in Great Britian, the Saybolt Viscosimeter in the United J
States, the Barbey Ixometre in France and a host of others. Most I
of them seem to have been devised with the idea in mind that the I
time of flow of a given quantity of various liquids through an
opening is approximately proportional to the viscosity, without
much regard to the character of the opening. There is usually
a container which is filled to a certain level and a short efflux tube
opening into the air. The number of seconds required for a given
quantity of liquid to flow out under gravity is taken as an indica-
tion of the viscosity.
As it was gradually realized that these times of flow were not
even proportional to the true viscosities, efforts have not been
wanting to reduce the times of flow to true viscosities. Since
the pressure is due to an average head of liquid h, the pressure is
hgp and the viscosity formula 1, p. 295, may be written
2-^-f
P *
Having obtained the values of the constants A and B by cali-
brating the viscometer with liquids of known viscosity it appears
possible to calculate the kinematic viscosity rj/p; but if absolute
viscosities are desired it is necessary to make a supplementary
determination of the density p. Thus elaborate tables and
charts have been devised for converting Engler " Degrees"
(cf. Ubbelohde (1907)), and Redwood (cf. Higgins (1913), Herschel
(1918) or Saybolt "Seconds") into true viscosities.
The widespread use of the Saybolt viscometer in this country
makes desirable the inclusion here of the specifications for its use
adopted by the American Society for Testing Materials.