The Magic of Capillary Action: How Far Will the Mercury Column Be Depressed?

How much will the column of mercury be depressed in the glass tube?

When a clean glass tube with a diameter of 3 mm is inserted vertically into a dish of mercury at 20°C, the column of mercury inside the tube will be depressed by a specific distance. What causes this phenomenon?

Understanding Capillary Action and the Depression of Mercury Column

When a clean glass tube is inserted into mercury, the column of mercury in the tube will be depressed. This is due to the fascinating phenomenon known as capillary action.

Capillary action is the result of adhesive and cohesive forces between the liquid (in this case, mercury) and the inner surface of the glass tube. The adhesive forces between mercury and the glass surface cause the liquid to rise, while the cohesive forces within the liquid hold it together. The balance between these forces determines the depression or rise of the liquid column.

The specific distance of depression can be calculated using the capillary rise equation:

h = (2γcosθ) / (ρgr)

Where:

• h is the depression (or rise) of the liquid column
• γ is the surface tension of the liquid (mercury in this case)
• θ is the contact angle between the liquid and the glass surface (usually close to zero for mercury and glass)
• ρ is the density of the liquid (mercury)
• g is the acceleration due to gravity
• r is the radius of the tube (half of the diameter)

By substituting the known values into the equation, including the surface tension of mercury, density of mercury, acceleration due to gravity, and the radius of the tube, the depression of the mercury column can be calculated.