106 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



(4) When solutions of cane sugar are heated to a temperature above 

 25°, the ratios of osmotic to gas pressure — which are all above unity 

 and are constant for each concentration at lower temperatures — begin 

 to decline. The decrease in the ratio with rising temperature is rela- 

 tively more rapid in dilute solutions than in concentrated ones. Such 

 conduct on the part of solutions is indicative of the presence in them 

 of dissociating hydrates. 



(5) The decline in the ratio of osmotic to gas pressure, which begins 

 a little above 25°, continues until, at some temperature which is char- 

 acteristic for each concentration, it becomes unity. This shows that, 

 at these temperatures, the osmotic pressures of all the solutions conform 

 both to the law of Gay-Lussac and to that of Boyle. 



(6) The work upon solutions of cane sugar, between the boiling- 

 point of the solvent and the temperatures at which the ratio of osmotic 

 to gas pressure becomes unity for the several concentrations, has not 

 been finished, but there is already in hand considerable evidence to the 

 effect that a ratio, having once become unity at some temperature, does 

 not further decline at still higher temperatures. 



(7) The conduct of glucose solutions differs somewhat but not wholly 

 from that of cane-sugar solutions: (a) At 0° the ratio of osmotic to 

 gas pressure is greater than unity, which again suggests hydration. The 

 ratio is, however, the same for all concentrations of solution. In other 

 words, the osmotic pressures are proportional to concentration. This 

 means that they conform to the law of Boyle. (6) At some temperature 

 above 0°, but below 10°, the ratio begins to decline, which suggests the 

 presence of dissociating hydrates. At 10°, half the difference between 

 the observed ratio at 0° and unity has already disappeared. But the 

 ratio is still the same for all concentrations, showing that the law of 

 Boyle holds at 10°, as well as at 0°. (c) At 25° and also at 30°, 40°, and 

 50° the ratio of osmotic to gas pressure is unity for all concentrations 

 from 0.1 to 1.0 weight-normal, proving that at these temperatures the 

 osmotic pressure of glucose solutions obeys both of the gas laws. 



(8) The ratio of osmotic to gas pressure in all solutions of mannite 

 is unity at 10°, 20°, 30°, and 40°. Its value at other temperatures has 

 not been ascertained. 



The mistaken impression that the author and his collaborators 

 are engaged in an endeavor to demonstrate that the gas laws apply 

 generally to osmotic pressure is probably due to the emphasis which 

 has frequently been laid upon the relations pointed out above. The 

 truth is, however, that they have limited their discussions to the few 

 facts established by themselves, and have only sought to formulate 

 the more obvious relations of their own experimental data. If any rule 

 proposed by them as apparently fitting their experimentally acquired 

 facts has been found susceptible of a concise mathematical expression, 

 it has not thereby acquired, in their estimation, any additional merit 



