The Chemistry of Cookery

those which crystallise in the same forms have similar rates of diffusion. The law that bears the most directly upon cookery is that ‘the quantity of any substance diffused from a solution of uniform strength increases as the temperature rises.’ The application of this will be seen presently. It may be supposed that if the jar used in Graham’s diffusion experiments were tied over with a mechanically air-tight and water-tight membrane, the brine or other saline solution thus confined in the jar could not diffuse itself into the pure water above and around it; people who are satisfied with anything that ‘stands to reason’ would be quite sure that a bladder which resists the passage of water, even when the water is pressed up to the bursting-point, cannot be permeable to a most gentle and spontaneous flow of the same water. The true philosopher, however, never trusts to any reasoning, not even mathematical demonstration, until its conclusions are verified by observations and experiment. In this case all rational preconceptions or mathematical calculations based upon the amount of attractive force exerted between the particles of the different liquids are outraged by the facts. If a stout, well-tied bladder that would burst rather than allow a drop of water to be squeezed mechanically through it be partially filled with a solution of common washing soda, and then immersed in distilled water, the soda will make its way out of the bladder by passing through its walls, and the pure water will go in at the same time; for if, after some time is allowed, the outer water be tested by dipping into it a strip of red litmus paper, it will be turned blue, showing the presence of the alkali therein, and if the contents of the bladder be weighed or measured, they will be found to have increased by the inflow of fresh water. This inflow is called _endosmosis_, and the outflow of the solution is called _exosmosis_. If an indiarubber bottle be filled with water and immersed in alcohol or ether, the endosmosis of the spirit will be so powerfully