196 REPORTS O? INVEISTIGATIONS AND PROJECTS. 



in addition to the above phenomena the changes due to the varying dissocia- 

 tion of the dissolved salt produced by the varying composition of the mix- 

 tures. 



These facts seem inexplicable on any other hypothesis than the one used, 

 namely, that when a salt of one of these elements is dissolved in any solvent, 

 both the molecules of the salt and the ions formed from thein become sol- 

 vated;that is, they combine with a certain number of molecules of the solvent. 



Morse, H, N., Johns Hopkins University, Baltimore, Maryland. Grant No, 

 500, The measurement of osmotic pressure of solutions. (For previous 

 reports see Year Books Nos. 2, 3, 4, 5, and 6.) $1,800. 



The principal work of the past year has been in two directions — first, in 

 that of bettering the apparatus and methods, and second, in that of measuring 

 pressure under the improved conditions, the ultimate purpose being to secure, 

 if possible, reliable evidence regarding the temperature coefficient of osmotic 

 pressure. 



The complex and difficult procedure of determining osmotic pressure had 

 previously been developed to a point where the results obtained were un- 

 doubtedly approximately correct, but yet not sufficiently precise to reveal 

 with certainty the exact relation of the force to temperature. There were, 

 in general, three principal sources of error in the method which have been 

 combated from the first, but which it was necessary to bring under still better 

 control before the object in view could be secured. 



There were, in the first place, a number of probable sources of error of 

 appreciable magnitude connected with the manometric portion of the work. 

 To eliminate these, an apparatus was devised which, in addition to increasing 

 the convenience and accuracy of calibration, made it possible to test and 

 compare the calibrated manometers under all pressures between i and 300 

 atmospheres. A new and more satisfactory apparatus for filling and finally 

 closing manometers was also devised; and the instruments were filled with 

 nitrogen instead of air, it having been observed that, however great the pains 

 taken to purify the mercury, there is an apparent slow decrease in the volume 

 of the gas when manometers filled with air are employed: An account of 

 this work has been given in a paper which appeared in the October number 

 of the American Chemical Journal. 



The largest errors in the more recent measurements of osmotic pressure 

 have been due to a dilution of the cell contents which resulted from the suck- 

 ing in of water from the wall while the cell was being closed at the beginning 

 and opened at the end of an experiment. With optically active substances, 

 like the sugars, it was easy to determine the total amount of dilution ; but, in 

 order properly to correct for it, it was necessary to know what proportion of 

 the whole dilution occurred at each period, since dilution occurring during the 



