### Theory:

A lactometer is a type of hydrometer. It is a device that measures the purity of milk, and it operates based on the gravity of milk.

Construction:
Lactometer
• The lactometer comprises a long calibrated test tube with a cylindrical bulb with a graduation of $$15$$ $$cm$$ at the top and $$45$$ $$cm$$ at the bottom.
• The test tube is completely filled with air. This air chamber causes the device to float when it is placed in the milk.
• In addition, the spherical portion of the bulb is filled with mercury to make the lactometer to sink up to the proper level and float in an upward position in milk.
• A thermometer is placed inside the lactometer, which extends from the bulb into the upper portion of the test tube where the scale is located.
• A proper lactometer reading be achieved only at a temperature of $$60$$ degrees Fahrenheit. A lactometer is an instrument that measures the amount of cream present in milk.
• The lower the lactometer floats in the milk, the more cream there is.
• Quality milk has an average reading of $$32$$.
• Lactometers are used in the milk production process.
Testing the purity of milk
Reference:
https://www.flickr.com/photos/ilri/13889870345