GLUCOSE. 189 



having developed the membranes at 30°, to measure the pressures of 

 glucose at that temperature before proceeding to develop them at 40° ; 

 and, having perfected them at 40°, to measure again the pressures of 

 glucose before proceeding to 50°, etc. On reaching 70° and 80°, at 

 which the measurement of the pressures of cane sugar was discontinued, 

 it is intended to determine the osmotic pressure of both substances 

 concurrently, for those and for all higher temperatures. It has been 

 suggested in a former chapter that perhaps membranes which have 

 served at high temperatures may be saved for work at lower tempera- 

 tures by reversing the process by which they were developed, that is, 

 by perfecting them at short temperature-intervals in the descending 

 order. This will be attempted after finishing the work upon glucose 

 and cane sugar at high temperatures. The prospect for success is not 

 regarded as very good ; since, hitherto, it has been found quite imprac- 

 ticable to rebuild effective membranes out of old ones which have 

 largely lost their semi-permeable character. It appears to make little 

 difference whether the damage to the membranes has resulted from a 

 great and too rapid fall in temperature, or from the action of electro- 

 lytes upon them. The only remedy for loss of osmotic activity which 

 has thus far been discovered is a persistent soaking of the membranes 

 in water. They often recover under this treatment. 



