256 PHYSIOLOGICAL PHYSICS. [Chap. xxn. 



This is one explanation offered to account for the 

 phenomena, an explanation, however, which is rejected 

 by Graham. It is supported by Liebig with many 

 ingenious experiments. 



Graham shows, by a series of experiments with 

 sulphate of magnesia, that when the strength of the 

 saline solution is increased in the osmometer, the 

 quantity of water and salt that exchange places is not 

 uniform. He concludes that the exosmose, to use 

 Dutrochet's term, of the salt is not due to pure diffu- 

 sion, for then the ratio between the exchanging water 

 and salt should remain constant. 



Etidosmotic equivalent is the term applied 

 to the weight of water that passes into the osmometer, 

 in exchange for unit weight of the salt that escapes 

 from it. It expresses the relation that exists be- 

 tween the increased bulk of fluid in the osmometer 

 and the diminished bulk of salt. Where the quantity 

 of water exceeds in bulk the quantity of salt the 

 osmosis is said to be positive ; where it is inferior, the 

 osmosis is said to be negative. End osmotic equivalent 

 was a term first applied by Jolly (1849), to whom the 

 idea of there being a relation between the bulk of 

 water and salt exchanged first occurred. His results 

 showed for 1 gramme caustic potash as much as 

 215-75 grs. of water, for 1 of sulphate of potash, 

 12-28 water, sulphate of magnesia, 11 '65, gum, 7'16, 

 chloride of sodium, 4-22, alcohol, 4'16. Since then 

 numerous observations have been made by German 

 observers, Harzer, Ludwig, Cloetta, Eckard, and 

 others, which show Jolly to have been mistaken in 

 supposing the equivalent to be constant. It varies 

 with the degree of concentration, with the tempera- 

 ture, and with other circumstances. 



As the degree of concentration increases, an in- 

 creased quantity of water enters the osmometer; but 

 it is soon observed, that if the concentration passes 



