Demos: 2B-01 Specific Gravity
Two different liquids, immiscible and having different densities, are placed in a U-shaped tube. By comparing the two heights shown, one can determine the relative densities of the liquids. If one liquid is water, the specific gravity of the other can be determined.
Since the pressure must be the same at the same height, we have
If r2 is water, then the calculated value r1 becomes the specific gravity of the that liquid.
Directions: The apparatus will likely be set up ahead of time, so no preparation is needed. For a quantitative analysis. measure carefully the distances h1 and h2.
Suggestions for Presentation: Without performing any calculations, ask the students if they can tell which of the two liquids has the greater density. Students will often have difficulty recognizing that the pressure must be the same at the same elevations. The level chosen in the diagram is merely a convenient one, but not necessary. Ask what would change in the equations above if a different level were chosen.