The Nicholson hydrometer is used to determine the specific gravity of a material more dense than water. The conical cup at the bottom should have enough lead in it that the cylinder floats upright in the water. An index mark is made on the the floating tube above the water level. Then three measurements are made: (1) weights are added to the top pan to press the float down to the index mark; (2) the substance whose density is desired is placed in the top pan and weights are added to depress the float to the index mark again; (3) the substance being examined is placed in the bottom pan and again weights are added to the top pan to bring the float to the index mark. From the values of the weights added in the three conditions the density of the substance can be computed.
Display Case B2