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Diffusion of Liquids

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-126

2025-11-08

590

Demonstration. - Fill a small jar three fourths full of water colored with blue litmus, and pour a small quantity of sulphuric acid carefully into the bottom of the jar through a thistle tube. The litmus will be colored red wherever the acid comes in contact with it. If now the jar is kept in a quiet place, the acid will pass through the litmus solution, and after a time the entire contents of the jar will be red. The rate at which the mixing takes place can be determined by fastening a meter stick to the jar in a vertical position and taking readings of the top of the red liquid at uniform intervals. It is interesting to observe that the plane which separates the two liquids is always exactly horizontal. This gradual molecular mixing of two liquids in contact with each other, which takes place even against the force of gravity, is called diffusion. Any liquids capable of mixing will diffuse, though at different rates.

Diffusion is a proof of molecular movements in liquids. It is the vibration of the molecules of sulphuric acid that forces them upward through the water, which is lighter than the acid. If the temperature is raised, the vibration is increased, and diffusion takes place more rapidly.