Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Casein, group of proteins precipitated when milk is mildly acidified. Casein constitutes about 80% of the total proteins in cow's milk and about 3% of its weight. It is the chief ingredient in cheese. When dried, it is a white, amorphous powder without taste or odor. Casein dissolves slightly in water, extensively in alkalies or strong acids.

Casein is used as a food supplement and as an adhesive, a constituent of water paints, and a finishing material for paper and textiles. A variety of casein, known by the modified name paracasein, is preferred for making a plastic, through the reaction of the casein with formaldehyde, that goes into the manufacture of buttons and other small objects. It is produced by adding the enzyme rennin to milk, forming a precipitate different from the material precipitated by acids.