How to Use an Ubbelohde Viscometer? By Zonwon Tech

An Ubbelohde type of viscometer is an instrument that measures viscosity using a capillary based method.  This particular type is recommended for measuring solutions with high viscosity because the values it obtains are separate from the total volume.  It was invented by Leo Ubbelohde (1877-1964) and bears his name.  The viscosity of a fluid is the measure of its resistance to deformation.  For example, as water spills out of a pitcher, it changes shape.  Honey would do the same but at a more gradual rate.  Therefore, water has a much higher viscosity than honey, for instance.  For liquids, the viscosity refers to “thickness.”  There are many different types of glass capillary viscometers because no single measuring instrument is suited for all viscosity determinations.  

However, Ubbelohde viscometers are all U-shaped glassware with a reservoir on one side and a measuring bulb with a capillary on the other.  Individual analysts have their preferences about which one to use.  Once you have the instrument that is suited to your own needs, follow the instructions below for how to use an Ubbelohde Viscometer. 

Step One

First, charge the viscometer with the fluid you are determining.  Put it into the first, large tube: the reservoir.  Be sure it is between the two lines on the tube so that the amount of liquid charged will not obstruct the Air Tube during use.  

Step Two

Next, connect clean, dry rubber tubing to the Timing Tube and the Air Tube, and place the viscometer in a temperature controlled liquid bath.  Here, the capillary must be vertical.  The sample liquid must come to the same temperature in the bath, and this will take about 20 minutes.  

Step Three

Next, seal off the rubber tubing that is connected to the air tube and gently suction it to the Timing Tube until the liquid reaches about 5 mm above the upper Timing Mark.  Hold the liquid at this level by sealing the tube.  Make sure that this point is at least 2cm below the bath liquid level.  

Step Four

Now, release the air tube to allow the liquid to fall away from the bottom of the capillary tube.  If the charge has a high viscosity, it is likely necessary to apply pressure to the air tube so that the liquid falls away from the bottom of the capillary tube.  

Step Five

Next, release the timing tube and allow the liquid to flow.  Measure the flow time in seconds for the bottom of the meniscus to pass from the top edge of the top Mark Line to the top edge of the Mark Line below it.  The time it takes for the liquid to pass through the two calibrated marks is a measure for the viscosity.  

Note, this device also has a third arm extending from the end of the capillary and open to the atmosphere.  This is so that the pressure head only depends on a fixed height and not the total volume of liquid, making the instrument a preferred measuring choice.