ALTANA Z7-Z10 Bubble Viscometers - Manual (Page 3)

DIRECTIONS FOR USING THE
GARDNER BUBBLE VISCOMETER A-5 to A-1
CAT. NO. PV-0500
This instrument is based on the principle that the
viscosity is directly proportional to the bubble
speed. The viscosity of a sample of varnish or
other transparent liquid is therefore determined
by reference to the standard tubes in which an air
bubble rises with the same speed as it does in a
tube of the sample being tested. For this purpose
two carefully calibrated empty tubes are furnished
with each set.
The bubble size of the sample is first adjusted as
nearly as possible to that in the standard tubes.
The tubes are then brought to a temperature of
25ºC (77ºF). This is essential due to the difference
in the temperature coefficient of viscosity of
mineral oils and varnishes. It is suggested that
a water bath be used, which quickly brings the
tubes to the proper temperature and insures
greater accuracy.
The bubble should be started from the flat end
of the tube held in a true vertical position. The
bottom meniscus of the bubble should be used
for comparing the samples. It is only necessary
that they start together. Owing to unavoidable
differences in bubble sizes and in the shapes of
the ends of the tubes, it may be necessary to raise
one of the tubes so that the points of comparison
will be on the same level. The observation is made
after the bubbles are completely formes and
moving upwards along a true vertical line. This
takes place about 1½ to 2 cm from the bottom of
the tube.
The standard empty grade “A” tubes have been
carefully selected to and I.D. of 10.65 ± 0.0025
mm. and should be used for exact determinations.
However, this close tolerance is relatively
expensive, and for the sake of economy, tubes
Directions for Using the Gardner Bubble Viscometer
2