194 PROFESSOR THOMAS GRAHAM'S SCIENTIFIC WORK. 



diffusion applied to analysis." When the solution of a saline or other 

 compound is separated from an adjacent mass of water by a membra- 

 nous septum, a greater or less quantity of the water very commonly 

 passes through the septum into the solution ; and if the solution be con- 

 tained in a vessel of suitable construction, having a broad membranous 

 base and a narrow upright stem, the water, in some cases, flows into the 

 vessel through the membrane, with a force sufficient to raise and sus- 

 tain a column of 20 inches or more of liquid in the stem. The problem 

 is to account for this flow ; which, with acid fluids more particularly, 

 takes place in the reverse direction — i. e. from the solution into the 

 water. 



In the course of his experiments Mr. Graham examined the osmotic 

 movement produced with liquids of most diverse character, employing 

 osmometers of animal membrane, albuminated calico, and baked earth- 

 enware. His results were, moreover, observed and recorded in very 

 great detail. As an illustration of these results, it may be mentioned 

 that with 1 per cent, solutions in the membranous osmometer, the liquid 

 rose in the stem 2 millimeters in the case of common salt, 20 millimeters 

 with chloride of calcium, 88 millimeters with chloride of nickel, 121 

 millimeters with chloride of mercury, 289 millimeters with j^roto-chloride 

 of tin, 351 millimeters with chloride of copper, and 540 millimeters with 

 chloride of aluminum. Mr. Graham showed, further, in opposition to 

 tke views of Dutrochet, that the velocity of the osmotic flow was not 

 proportional to the quantity of salt or other substance originally con- 

 tained in the solution; and that the flow did not depend on capillarity', 

 as Dutrochet had inferred; or yet on diffusion, as some of his own 

 experiments might be thought to indicate. Eventually he was led to 

 the conclusion that osmose was essentially dependent on a chemical 

 action taking place between one or other of the separated liquids and 

 the material of the septum. He appears to have held somewhat 

 different views of the nature of this chemical action at different times, 

 and not to have considered it as being in all cases of the same character. 



The following extracts, exjjressing his latest views on the subject, are 

 taken from the conclusion of his paper " On li(]uid diffusion applied to 

 analysis." 



'-'■ It now appears to me that the water movement in osmose is an affair 

 of hydration and of dehydration in the substance of the membrane, or 

 other colloid septum, and that the diffusion of the saline solution placed 

 within the osmometer has little or nothing to do with the osmotic result 

 otherwise than as it affects the state of hydration of the septum. * * ^ 

 Placed in pure water, such colloids (as animal membrane) are hydrated 

 to a higher degree than they are in neutral saline solutions. Hence the 

 equilibrium of hydration is difterent on the two sides of the membrane 

 of an osmometer. The outer surface of the membrane being in contact 

 with pure water, tends to hydrate itself in a higher degree than the 

 inner surface does, the latter surface being supposed to be in contact 



