Lactometer is q hydrometer instrument that is used to check for the purity of milk by measuring milk’s density usually it works on the principle of gravity of milk which leads to find out the content of the water in milk or to test the richness of the milk .Lactometer is consists of a long narrow graduated glass stem which is enlarged in the end into a hollow glass bulb weighted with mercury and lead shots. Numbers registered on the lactometer scale range from 10 or 15 to 40, which record Quevenne’s degrees.The mechanism of lactometer is based on the Archimedes Principle, when body floats in a liquid it displaces an amount of liquid equal in weight to the weight of the floating body.