ASTM D1545 for Viscosity of Transparent Liquids by Bubble Time Method
4. Procedure
4.1 Fill a standard viscosity tube with the material to be tested to approximately level with the 108-mm line.
4.2 Transfer the tube to a constant 25°C temperature bath with the cork loosely inserted. Hold at this temperature for 10 min.
NOTE 3 - Adequate control of the temperature bath is essential. A variation of 0.1°C in the temperature of the bath will cause a 1 % variation in the timed bubble travel.
4.3 At the end of 10 min adjust the level of the liquid so that the bottom meniscus will be level with the 100-mm line. Insert the cork so that the bottom of the cork is on the level with the 108-mm line. This will ensure a bubble of suitable and uniform size.
4.4 Insert the tube in the rack and immerse in the 25°C water bath. Allow the tube(s) to stand with cork down in the bath a minimum of 20 min before determining the viscosity.
NOTE 4 - For viscosities of liquids that have a timed bubble travel of 4 s or less, more precise results can be obtained by comparison against reference standards having a predetermined viscosity or timed bubble travel.
4.5 To read, invert the tube quickly and determine the time required for the bubble to rise in seconds. When determining the time in seconds start the timing device when the top of the bubble becomes tangent to the 27-mm line on the tube. Stop the timing when the top of the bubble becomes tangent with the 100-mm line. This gives a 73-mm timed bubble travel. All timings shall be made with the tube in an exact vertical position.
NOTE 5 - Positioning of the tube in a vertical position is mandatory. A tube one radius off the vertical will give an error of approximately 10 % in the time of bubble travel.
