CHEMISTRY — MORSE. 153 



the subject of osmotic pressure. The view hitherto held regarding 

 this force has been authoritativel}^ expressed in the following words : 

 Dissolved substances exert the same pressure , in the form of osmotic pres- 

 sure, as thev would exert luere they gasified, at the same temperature , 

 without change of volume . 



It was known, ho.wever, that onh' very dilute solutions conform 

 to this rule — that in concentrated solution the pressures are much 

 higher than can be accounted for by it. 



The final success of the long-continued efforts to solve the problem 

 of the production of a j^er^dceable cell has made it impossible to meas- 

 ure the pressure of all concentrations of solutions with considerable 

 precision, and the first results obtained indicate that the pressure of 

 concentrated solutions are not less normal than those of dilute solu- 

 tions, provided certain relations hitherto misapprehended are taken 

 into account. 



The rule which is deduced from the results of the measurements 

 which have been made is as follows : Cane sugar dissolved in water 

 exerts an osmotic pressure equal to that which it would exert if it 

 were gasified at the same temperature and the volume of the gas were 

 reduced to that of the solvent in the pure state. In other words, the dis- 

 solved substance exerts throughout the larger volume of the solution 

 an osmotic pressure equal to the pressure which it, as a gas, would 

 exert if confined to the smaller volume of the pure solvent. 



The most concentrated solutions conform to this rule, as well as 

 do the most dilute, and all concentrations which have thus far been 

 tested are in satisfactory agreement with it. 



Some work has also been done upon the supposed abnormal freez- 

 ing points of concentrated solutions of cane sugar, and it appears 

 that, if the relations which have been found to hold for the osmotic 

 pressure of such solutions are taken into account, the abnormalities 

 of freezing-point depression disappear in the sense that all concen- 

 trations conform to the same rule. 



The measurement of osmotic pressure will now be extended as 

 rapidly as possible to solutions of other substances, in order to deter- 

 mine whether the relations discovered in the case of cane sugar are 

 of a general character. 



