282 CARNEGIE INSTITUTION OF WASHINGTON. 



(3) That between 0° and 25° the osmotic pressure is, in all cases, 

 greater than the calculated gas-pressure of the solute, which suggests 

 a concentration of the solutions through a hydration of the solute 

 and may, therefore, explain the apparent nonconformity between 

 these temperatures of osmotic pressure to the law of Boyle. 



(4) That somewhere between 25° and 30° the ratio of osmotic to 

 gas pressure, which between 0° and 25° is greater than unity but 

 constant for each concentration, begins to decline — rapidly in the 

 more dilute and less rapidly in the more concentrated solutions, as if 

 hydrates were dissociating and the solutions were becoming more 

 dilute in consequence. 



(i) That this decline in ratio continues with rising temperature 

 until, at some temperature which is characteristic for each concen- 

 tration of solution, it becomes unity, which shows that at these tem- 

 peratures the osmotic pressures of all the solutions are conforming 

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



The temperature at which the ratio became unity in the most 

 dilute solution (0.1 weight-normal) was 30°, while that at which it 

 became unity in the most concentrated solution (1.0 weight-normal) 

 was 80°. The unit ratio for each of the intermediate concentrations 

 was reached at some temperature between 30° and 80°. 



It was considered very important to measure the osmotic pressure 

 of all ten concentrations of solution at temperatures between those 

 at which the ratios became unity and the boiling-point of the solvent, 

 in order to ascertain if the unit ratio, once reached, persists through 

 all the higher temperatures. All possible preparations were made to 

 meet the extraordinary difficulties which are experienced in measur- 

 ing osmotic pressure at high temperatures, and it was expected to 

 resume the work in September 1913 where it had been discontinued 

 at the end of the previous June. It was found in the fall, however, 

 that the membranes in all of the cells which had been used at temper- 

 atures above 40° had deteriorated during the summer and were unfit 

 to measure osmotic pressure at high temperatures. This deterio- 

 ration was a surprise, because it had been found in all previous 

 work that the quafity of the membrane was improved by the summer 

 soaking in pure water, i. e., water free from electrolytes, an effect which 

 we have ascribed to an improvement in their colloidal character. 

 Three months were spent in endeavoring to bring the membranes 

 again into good condition. All the modes of treatment which had 

 been found efficacious for membranes used at moderate temperatures 

 only were employed, but without success. It was finally decided to 

 discard all of the cells which had been used at high temperatures the 

 previous year and to make new ones for the continuation of the work. 



The mere making of the cells — involving the preparation of the 

 clays, also the pressing, the shaping, the burning, the grinding, and 



