198 



REPORTS OF INVESTIGATIONS AND PROJECTS. 



Three series of measurements of osmotic pressure were carried out under 

 the improved conditions just outlined, and a fourth one is nearly finished. 

 It is believed that the errors in these determinations are limited to the second 

 decimal place in the numbers expressing the observed pressures, which is a 

 degree of accuracy hitherto unattainable. The eflfect of this increase in pre- 

 cision is observable in the temperature coef^cient of osmotic pressure which 

 is brought to light by the recent work. 



One series of measurements at 10° was made with glucose solutions, which 

 varied by tenths from o.i to i.o weight-normal concentration. A summary 

 of the results is given in the following table : 



Summary of Results — Mean Values. 



The definite conclusions to be drawn from the table are: (i) that, at 10°, 

 as had previously been found at other temperatures, the osmotic pressure of 

 glucose solutions is strictly proportional to their weight-normal concentra- 

 tion ; (2) that, at this temperature, the osmotic pressure of glucose solutions 

 exceeds gas pressure by 3 per cent, as will be seen in the column under 

 "Ratio of osmotic to gas pressure." At 0° the excess of osmotic over gas 

 pressure had been found to be about 5 per cent, but this value will be some- 

 what changed when the work at 0° is repeated under the recently improved 

 conditions. 



If the results at 10° are compared with the earlier but less reliable ones at 

 0°, the existence of a decided temperature coefficient is discernible, but it 

 would be premature to discuss its magnitude until the work at 0° has been 

 repeated and the pressures at still other temperatures have been determined. 

 As soon as practicable, series of measurements at 0°, 5°, 15°, 20°, 25°, and 

 30° will be carried out. An account of the work upon glucose solutions at 

 10° will be found in the July number of the American Chemical Journal. 



