Figure 24 - Density of nonmiscible liquids by balanced columns
Liquids in Communicating Tubes. — Let two liquids that do not react chemically be placed in a bent tube (Figure 24). When the liquids are at rest, the less dense liquid stands at a height h1 above the junction of the two liquids. The pressure exerted by this column of lighter liquid is just balanced by the weight of the column of heavier liquid that stands above the junction of the liquids. Let d1 be the density of the lighter liquid, d2 the density of the heavier liquid, h1 the height of the lighter liquid above the junction, and h2 the height of the heavier liquid. Then
h1 x d1 = h2 x d2 ,
h1 d1
–– = –––
h2 d2
Hence, the heights of the two liquids above their surface of separation are inversely proportional to the densities of the liquids.
In case the liquids react chemically, the bent tube is inverted and the ends are placed in cups containing the liquids (Figure 25) whose densities will be denoted by d1 and d2. The air from the upper part of the bent tube is partly removed and the stopcock closed. The pressure above both liquids inside the tube is the same, and the atmospheric pressure on the liquids in the open vessels is the same. The difference between the pressure inside the tube and the atmospheric pressure is in each case balanced by the rise of the liquid in the tube. These differences in pressure are the same and