Question

Lactometers are used to determine the purity of a sample of milk. On which principle is this instrument based?

Answer 1

Lactometers are used to check the purity of milk. It is a type of hydrometer. They can be calibrated to one or more scales. Liquids have densities and this property can be used to check for their properties. There are various kinds of hydrometers that are used.

Complete answer: As we know that the Lactometer is basically a small glass instrument which is generally used to measure the density or creaminess of the milk. This instrument is also used to check adulteration in the milk. Such an instrument works on the Archimedes principle. Any solid that is suspended in a fluid can be upheld by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid.
This instrument usually works on the principle of Archimedes’ and uses the specific gravity of milk by measuring the relative density of the milk with respect to that of water. If the result of specific gravity is within the range then the milk is pure means no water is added into the milk.
Also, this instrument consists of a long test tube and a meter bulb is attached to it. When we pour the milk into the vessel, the meter bulb starts floating on it. And it basically tells us about the density of the milk. The lower the density of milk, the deeper the lactometer will sink.
We can also check the quality of milk by formation of cream. The milk is first poured into this apparatus and allowed to stand still until the formation of cream, the depth of cream deposited on the apparatus tells us about the quality of milk. If our given sample is pure, the lactometer will float and if it is adulterated then the lactometer sinks.
Therefore, from the above explanation we can say that the lactometers work on the Archimedes’ principle.

Note: Always remember that the Lactometers are based on the density or specific gravity of the milk. They do not give any information about the composition of the milk since milk contains a variety of dissolved substances. They are a type of hydrometer and such kind of hydrometers are used for different purposes. For example, saccharometer is used to measure the density of sugar in liquid. An alcohol meter is used to measure higher levels of alcohols in spirit.