CHEMICAL SCIENCE. 225 



merged in water,) the passage of the salt outward is entirely by diffusion, 

 and that a thin membrane does not sensibly impede that molecular process. 

 The movement is confined to the liquid salt particles, and does not influ- 

 ence the water holding them in solution, which is entirely passive : it 

 requires no further explanation. The flow of water inwards, on the other 

 hand, affects sensible masses of fluid, and is the only one of the movements 

 which can be correctly described as a current. It is osmose and the work 

 of the osmotic force to be di c cussed. As diffusion is always a double 

 movement, while salt diffuses out, a certain quantity of water necessarily 

 diffuses in at the same time, in exchange, diffusibility might be imagined 

 to be the osmotic force. But the water introduced into the osmometer in 

 this way has always a definite relation to the quantity of salt which es- 

 capes, and cm scarcely rise in any case above four or six times the weight 

 of salt ; while the water entering the osmometer often exceeds the salt, 

 leaving it at least one hundred times : diffusion, therefore, is quite insuf- 

 ficient to account for the water current. The theory which refers osmose 

 to capillarity appears to have no better foundation. The great inequality 

 of ascension assumed among aqueous' fluids is found not to exist when 

 their capillarity is correctly observed, and many of the saline solutions 

 which give rise to the highest osmose are indistinguishable in ascension 

 from pure water itself. Two series of experiments on osmose were 

 described : the first series made with the use cf porous mineral septa, and 

 the second series with animal membrane. The earthen- ware osmometer 

 consisted of the porous cylinder employed in voltaic batteries, about five 

 inches in depth, surmounted by an open glass tube 0.6 inch in diameter, 

 attached to the mouth of the cylinder by means of a cup of gutta percha. 

 In conducting an experiment, the cylinder was filled with any saline solu- 

 tion to the base of the glass tube, and immediately placed in a large jar of 

 distilled water ; and as the fluid within the instrument rose in the tube, dur- 

 ing the experiment, water was added to the jar so as to prevent inequality 

 of hydrostatic pressure. The rise (or fall) of liquid in the tube was highly 

 uniform, as observed from hour to hour, and the experiment was generally 

 terminated in five hours. From experiments made on solutions of every 

 variety of soluble substances, it appeared that the rise or osmose is quite 

 insignificant with neutral organic substances in general, such as sugar, 

 alcohol, urea, tannin, &c. ; so also with neutral salts of the earths and 

 ordinary metals, and with chloride of sodium and potassium, nitrates of 

 potash and soda, and chloride of mercury. A more sensible but still very 

 moderate osmose is exhibited by hydrochloric, nitric, acetic, sulphurous, 

 citric and tartaric acids. These are surpassed by the stronger mineral 

 acids, such as sulphuric and phosphoric acid and sulphate of potash ; which 

 are again exceeded by salts of potash and soda, possessing either a. decided 

 acid or alkaline reaction, such as binoxalate of potash, phosphate of soda, 

 and carbonates of potash and soda. The highly osmotic substances were 

 also found to act with most advantage in small proportions, producing 

 in general the largest osmose in the proportion of one-quarter per cent, of 

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