NON-DIFFUSIBILITY. 



105 



of which rises a graduated tube. The osmoraeter is supposed to 

 contain a solution of some salt ; sulphate of copper, for instance. 

 In a short time after the apparatus has been put in the condition 

 described, the water in the jar will become bluish from the pas- 

 sage into it of some of the sulphate of copper from the osmometer. 

 This outward passage of the salt is exosmosis. In the graduated 

 tube the fluid in the osmometer will be seen to rise higher and 

 higher, due to the passage of the distilled 

 water from the jar through the parchment 

 into the osmometer, lowering the level of the 

 water in the jar. This inward passage con- 

 stitutes endosmosis. This continues until the 

 proportion of sulphate of copper is the same 

 in both jar and osmometer ; in the mean- 

 time, however, the amount of water in the 

 osmometer is greater than at the beginning 

 of the experiment. If different solutions 

 are used than those mentioned, the results 

 as to time, amount of endosmosis, etc., will 

 vary materially from those described. 



This subject was exhaustively studied by 

 Graham, who objected to the use of the 

 terms " endosmosis " and " exosmosis," be- 

 lieving that there was in reality but one 

 current, the inward one; and he therefore 

 used only the terms osmosis and osmotic. In 

 the outward passage of the salt he held that 

 it was the particles of salt which passed, but 

 not the water holding them in solution. 



A second experiment may be performed 

 which illustrates another phase of osmosis. 

 From one end of a hen's egg the shell is 

 to be carefully removed so as to leave the 

 membrane uninjured. Through the other 

 end, into the interior of the egg, a glass tube is to be passed, and 

 the place at which it enters the egg closed with sealing-wax. The 

 egg is then to be placed in a wine-glass containing distilled water. 

 The water in the wine-glass passes through the membrane into the 

 egg, and the yolk will be seen to rise in the glass tube ; at the same 

 time it will be noted that the water in the wine-glass is diminished. 

 After a time a solution of nitrate of silver may be dropped into the 

 wine-glass, and immediately a whitish precipitate forms, consisting 

 of silver chlorid. This is* a proof that the chlorid of sodium, or 

 common salt, which was a constituent of the egg, has passed through 

 the membrane into the water. Other tests will show that the other 

 salts have also passed out, but that little of the albumin has come 

 through. From this experiment it will be seen that substances act 



FIG. 84. Graham's os- 

 mometer. 



