Does Capillary Forces Exist? (Part 1)

In school you may have been told that thin tubes can lift water just because they are thin? Maybe you have been told that the meniscus is pulling the water up the inside of the tube? Maybe you have seen it with your own eyes?

Maybe you have seen drawings like this one?

What do you think?

Will there be more water lifted on the inside of a glass tube than on the outside?

If you answer this question correctly you may become one of six to win a small gift.

Substantiated answers will be favored, and the gift will be sent to the winners by mail.

Hydrophilic have done some fun and carefully thought out experiments to investigate this. In one week (July 14th) the result will be posted, and the clever winners will be named 😊

Experimental set-up and procedure

To check if more water is lifted on the inside than on the outside of a glass tube the following tools were used:

Tool 1 : Glass tubes

The glass tubes are marketed as “Capillary Tubes”, 100 mm long, 1.2 mm internal diameter and 1.65 mm external diameter. One glass tube weigh 0.2770 gram.

For each new experiment a new glass tube is taken straight from the box. This is to prevent changes in surface chemistry – e.g. changes amount of water on surface.

Tool 2: Camera bellow with tube holder

A specially bent wire to hold the glass tube during the measurement mounted on a Pentax camera bellow (from the 1970s). The camera bellow was chosen because it was easily available and perfect for lowering a thin glass tube into water in a controlled manner with no unwanted up/down movements.

Tool 3: The Tank

A tank with depth markings and a millimeter scale. The tank is made of plexiglass for optimal transparency. There is 42 mm between the two black lines (A & B).

Tool 4: SFW

The water used is saline in order to reduce evaporation. Density is 1,0533 g/ml. Water will be filled to a level 2 mm above the upper line (A) during the experiments.

Tool 5: Analytical Scale

A scale that can measure mass as a function of time with better than 1 mg precision.

Filtering out disturbing effects

Glass tube buoyancy effect

To be able to accurately measure the weight lifted by the glass tube (inside + outside) the buoyancy effect from the glass tube must be eliminated. This is done by multiplying the wall volume of the glass tube (1.01 mm3/mm) with the depth of the glass tube and the density of the water (1.0533 mg/mm3).

The resulting buoyancy effect becomes 1.064 mg/mm.

Evaporation

Even saline water (SFW) evaporates a little bit. The weight of the tank with water was measured over a 900 seconds time period immediately before the experiment. The side doors of the scale were closed and top window open during the evaporation measurement – this is same situation as during the experiment.

The evaporation was found to be 3.0 mg/minute

Experimental Procedure

The weight of the tank is recorded as a function of time – one reading per second.

Evaporation effect is eliminated by adding 3 mg/minute to the actual scale reading.

Tube held steady above water long enough to prove stable situation.

Glass tube lowered to upper black line (position A) while weight is recorded:

The glass tube is then lowered to the lower black line (position B) and then back to the upper black line (position A). The weight is continuously recorded, and the height of the water inside the tube (at position A and B) is read from the millimeter scale attached to the tank (ref. Analytical Scale picture above).

The buoyancy effect has not been filtered out in the graph above: at position B the buoyancy effect is 46.7 mg, and at position A it is 2.1 mg.

The results will be posted on July 14th.

If you want to become a winner, you must post your answer to this question:

Will there be more water lifted on the inside of a glass tube than on the outside?