2i6 re;ports of inve;stigations and projects. 



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

 569. Study of the measurement of the osmotic pressure of solutions. 

 (For previous reports see Year Books Nos. 2, 3, 4, 5, 6, and 7.) 



$1,800. 



The work of the past year has had for its object the determination, with 

 all possible accuracy, of the relation of osmotic pressure to temperature. To 

 this end, our efforts have been primarily in the direction of improvements in 

 method, though many satisfactory measurements of pressure have been made. 



The improvements in method to which attention has been given may be 

 classified under the following heads : "Cells," "Membranes," "Manometers," 

 and "Devices for the regulation of temperature." A high degree of perfec- 

 tion in all of these is essential to any authoritative determination of the tem- 

 perature coefficient of osmotic pressure. 



(i) Cells. — The test of excellence in a cell is its ability to maintain undi- 

 minished the concentration of the inclosed solution. So long as the solution 

 suffers dilution during a measurement it is impossible, as has been explained 

 elsewhere, to ascertain precisely its osmotic pressure. But the construction 

 of cells which exclude all of the numerous sources of possible dilution has 

 been, from the first, a problem of the greatest difficulty, and one whose solu- 

 tion has required ten years of continuous effort. During the past year the 

 last of our difficulties in this direction has been overcome, and none of the 

 solutions whose pressure has been measured during the latter part of the year 

 1908-09 has shown any loss in concentration which could be detected by the 

 polariscope. The improvements in cells which eliminated the major portion 

 of the dilution of the solutions were described in a paper which appeared in 

 September, 1908 (American Chemical Journal, xl, 266). The subsequent 

 ones, which finally suppressed all loss in concentration, will be described in 

 a later communication. 



(2) The membranes. — ^The suppression of all dilution, through improve- 

 ments in cell construction, was a final demonstration of the truly semiperme- 

 able character of the membrane, but it was observed, as the measurements of 

 pressure, from various causes, became more precise, that, on some occasions, 

 notwithstanding the cell contents showed no loss in concentration, the solu- 

 tions failed, by small amounts, to develop the highest pressures which had 

 been observed at other times. These discrepancies, which were of little im- 

 portance as long as the sources of error in the method were numerous and 

 large, became a matter for serious attention during the past year. The mem- 

 brane can not be studied directly, and any conclusions regarding the cause or 

 causes of its misconduct on any occasion must be based upon what is known 

 of the conditions under which it was formed ; hence the definite location of 

 a defect, or of the cause of imperfect action, is usually a matter of consider- 

 able trouble in the case of osmotic membranes. Nevertheless, we were able 



