APPENDIX C

327

cup). Viscosity determinations shall be made in a room free
from draughts, and from rapid changes in temperature. All oil
introduced into the standard oil tube, either for cleaning or for
test, shall first be passed through the strainer.
"To make the test, heat the oil to the necessary temperature
and clean out the standard oil tube with the plunger, using some
of the oil to be tested. Place the cork stopper into the lower
end of the air chamber at the bottom of the standard oil tube.
The stopper should be sufficiently inserted to prevent the escape
of air, but should not touch the small outlet tube of the standard
oil tube. Heat the oil to be tested, outside the viscometer, to
slightly below the temperature at which the viscosity is to be
determined and pour it into the standard oil tube until it ceases
to overflow into the overflow cup. By means of the oil tube
thermometer keep the oil in the standard oil tube well stirred and
also stir well the oil in the bath. It is extremely important that
the temperature of the oil in the oil bath be maintained constant
during the entire time consumed in making the test. When the
temperature of the oil in the bath and in the standard oil tube are
constant and the oil in the standard tube is at the desired tem-
perature, withdraw the oil tube thermometer; quickly remove the
surplus oil from the overflow cup by means of a pipette so that
the level of the oil in the overflow cup is below the level of the oil
in the tube proper; place the 60-ml flask in position so that the
oil from the outlet tube will flow into the flask without making
bubbles; snap the cork from its position, and at the same instant
start the stop watch. Stir the liquid in the bath during the run
and carefully maintain it at the previously determined proper
temperature. Stop the watch when the bottom of the meniscus
of the oil reaches the mark on the neck of the receiving flask.
"The time in seconds for the delivery of 60 ml of oil is the
Saybolt viscosity of the oil at the temperature at which the test
was made."
There is little to recommend any one of these instruments
except their wide use in their respective countries. They are
inaccurate and in the case of viscous oils time-consuming. With
volatile solvents they cannot be used at all due to evaporation.
The greatest source of error in the technical instruments is due
to poor temperature control. The bath around the container is