Lactometer is a small glass instrument that is used to test the purity of the milk. It works on the principle of specific gravity of milk (Archimede’s Principle). It measures the relative density of milk with respect to water. If the specific gravity of a sample of milk is within the approved ranges, the milk is pure. If it is not, then there is some adulteration.
The Archimedes theory is concerned with the forces exerted on an object by the fluids that surround it. The net weight of an object immersed in a fluid is reduced by this applied force. This physical law of buoyancy also assists in our understanding of how ships float in water. Archimedes’ principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether partially or fully submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.