112 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



which the so-called preliminary measurements fall, the chief concern 

 of the writer and of his collaborators was to perfect the means of 

 maintaining constant temperature, to lessen the time required for the 

 opening and closing of the cells, and to develop a cell whose capacity 

 could not increase under pressure. Minor sources of error, of which 

 there are many, were not neglected, but the attention given them was 

 strictly proportional to the relative magnitude of their effects upon 

 the precision of the results. After thermometer effects and dilution, 

 more attention was given to the improvement of the manometers than 

 to any other feature of the method. 



The second period begins with Series I, in which the fluctuations 

 in bath temperature amounted, in some instances, to whole degrees, 

 and in which the dilution of the cell contents, though unknown, must 

 have been very large; and it closes with Series VIII, which was carried 

 through without any material variation in bath temperature and with- 

 out any dilution of the cell contents which could be detected by the 

 polariscope. 



The part played by the first eight series in the evolution of the method 

 gives them great importance in the history of the investigation, but 

 the actual results of the measurements are to be considered and 

 appraised merely as tests of progress in the development of the method. 

 They will be treated as such throughout by the writer, and not dis- 

 cussed, to any considerable extent, with reference to the light which 

 they throw upon the true osmotic pressure of cane-sugar solutions. 



Series I.* 



The cell employed in this series was that seen in Figure 7, page 19. 

 The closing and the opening of such a cell are difficult and strenuous 

 performances, which require the cooperation of two experienced persons. 

 Both operations will be briefly described because of the bearing they 

 have upon the dilution of the cell contents which it was so difficult to 

 suppress. 



In closing, one of the operators (No. 1) holds in one hand the filled 

 cell, which is covered with a piece of very thin rubber tubing to prevent 

 any soiling of the outside of the cell by the overflow of the solution or 

 by the hand. With the other hand he holds and manipulates the 

 manometer, the nut (h, Figure 7) resting upon the back of the hand 

 which grips the manometer by the rubber stopper (k). The duty of 

 operator No. 2 is to manipulate the "fang" (Figure 8), by means of 

 which the rubber is w r orked into the cell and an equal amount of the 

 solution is let out of it; and afterwards to wrap and tie with twisted 

 and waxed shoemakers' thread the exposed part of the stopper when 

 it has been forced to a sufficient depth into the glass tube (B). 



♦Measurements by H. N. Morse and J. C. W. Frazer. Am. Chem, Jour., xxxiv, 1. 



