C. E. Linebarger — Nature of Colloid Solutions. 221 



may be frozen or heated to 150° without alteration. I have 

 therefore made some determinations of the osmotic pressure of 

 solutions of colloid tungstic acid in the hope of obtaining results 

 that may throw some light upon the nature of colloid sub- 

 stances in solution. As osmotic pressure affords a precious 

 means, according to the theory of van't Hoff on dilute solutions, 

 of determining molecular mass, the results should have some 

 interest. . 



The apparatus used consisted simply of a tube about 8 cm long 

 and 15 mm in diameter ; one end was well-rounded off in the 

 flame and the other drawn out so as to form a neck. The 

 manometer was a capillary tube with a bore of about 0'5 mm , 

 passing loosely into the neck of the osmometer. A bit of 

 rubber tubing is used instead of a cork. The manometer 

 should be so adjusted that it may be pushed to and fro in the 

 osmometer. This is accomplished by greasing well the interior 

 of the rubber tubing. By pushing the manometer into the 

 osmometer or by drawing it out, the pressure may be increased 

 or decreased at pleasure. The membrane used was thick parch- 

 ment paper, which was bound over the wide end of the tube 

 by means of silk thread, perfect contact between the paper and 

 the glass being effected by the use of a solution of good sealing 

 wax in alcohol. A hermetic joint may thus be obtained. Of 

 course, a great degree of accuracy cannot be obtained with an 

 apparatus of the above description, especially when it treats 

 of measuring high pressures. Still with pressures not exceed- 

 ing 30-40 om of mercury quite good measurements can be made. 

 I have modified the apparatus somewhat, so that it is capable 

 of much greater precision. The results obtained with the 

 second apparatus will be published in a succeeding paper. 



The osmometer is filled with the solution, the osmotic 

 pressure of which is to be determined and the manometer in- 

 serted in the neck, care being taken that no bubbles of air be 

 present. The osmometer is then suspended vertically in a jar 

 filled with pure water. 



Two solutions of colloid tungstic acid were prepared, which 

 I will designate by the Roman numerals I and II. 



1 c. c. of sol. I contained -02467 grms. (H 2 W0 4 ) n 

 1 c. c. of sol. II contained -0100 grms. (H 2 W0 4 ) n 



The solution of tungstic acid was prepared by adding to a 

 •5 per cent solution of sodium tungstate just enough hydro- 

 chloric acid to take up the sodium. The whole was dialyzed 

 until no trace of salt could be detected in the outer liquid. 



I filled an osmometer with sol. I, adjusted the manometer 

 so that the pressure was about 20 cm of the solution, as I did 

 not employ mercury in the manometer in this experiment, and 

 suspended the apparatus in pure water. The solution mounted 



