222 CONCLUSION. 



compounds selected for the purpose were cane sugar, glucose, levulose, 

 and mannite. Some of the reasons for this choice of materials are 

 given below : 



(1) All four of the compounds named separate from solution without 

 water of crystallization, which simplifies the situation by making it 

 possible, for a time, to evade the question whether such water, when 

 a substance is dissolved, belongs to the solute or to the solvent. 



(2) The list includes substances which are both normal and also, in 

 different ways, abnormal in respect to their freezing-point depressions. 

 These compounds therefore afford an excellent opportunity for com- 

 paring experimentally determined osmotic pressures with a variety of 

 freezing-point depressions. 



(3) Three of the compounds are optically active, and alterations in 

 the concentration of their solutions can be readily detected and meas- 

 ured by the polariscope. Mannite, the fourth substance, was selected, 

 notwithstanding its optical inactivity, because the depression of the 

 freezing points of its solutions are all normal; and, since the intro- 

 duction of the interferometer, the lack of optical activity is no longer 

 an objection to it. 



It was proposed to measure the pressures of the enumerated sub- 

 stances from 0° to the highest temperature at which it is practicable 

 to work — possibly to 100°. It was thought that, by extending the 

 investigation over a wide range of temperature, much light might be 

 obtained on the problem of hydration and its relation to the freezing- 

 point depressions and osmotic pressures of solutions. The work is now 

 in its second stage — in that stage, namely, in which the osmotic pressure 

 of cane sugar, glucose, levulose, and mannite is under investigation. 

 About three years more will be required to complete the proposed 

 study of these substances. 



Having finished the investigation of the anhydrous compounds men- 

 tioned above, it is proposed to study, in a similar manner, several of 

 the carbohydrates which separate from solution with water of crystal- 

 lization. It is also proposed to continue the investigation of the 

 osmotic pressure of electrolytes. 



Lists of those osmotic pressures which the author regards as estab- 

 lished with a reasonable degree of certainty are to be found : 



(1) For cane sugar, in Tables 59, 60, and 62, pages 184 and 186. 



(2) For glucose, in Table 67, page 196. 



(3) For mannite, in Tables 72 and 73, page 207. 



The conclusions which were drawn from them have been sufficiently 

 discussed from time to time in the course of this report. 



