598 COLLOIDAL BEHAVIOR OF EDESTIN 



freed from sodium chloride by washing repeatedly with 50 per cent 

 alcohol, and was partly dried by washing with absolute alcohol and 

 then with ether, which left it with a moisture content of 10.1 per cent 

 as determined by heating to constant weight at 1 10°C. The dry pow- 

 der was found to contain 18.4 per cent of nitrogen, as determined by a 

 micro-Kjeldahl method accurate to about 1 per cent, whereas Osborne^ 

 reported 18.69 per cent of nitrogen. Under the microscope the 

 preparation appeared to have the form of fragments of crystals. 



The isoelectric point of edestin was given by Rona and Michaelis* 

 as at a hydrogen ion concentration of 1.3 X 10~^ (pH 6.89). This 

 was the point of maximum precipitation obtained by using a series 

 of phosphate buffers.® Attempts were made to determine the iso- 

 electric point of the present preparation by similar methods, but the 

 point of maximum precipitation seemed to vary with the buffer used. 

 Most of the values obtained, however, lay between pH 5 and 6. 

 Measurements of the osmotic pressure developed in collodion bags 

 by suspensions of edestin in various concentrations of very dilute 

 sodium hydroxide indicated a minimum between pH 5 and 6. Elec- 

 trophoresis experiments with suspensions of this edestin were made by 

 Dr. John H. Northrop of this laboratory, who also obtained different 

 results with different buffers, which indicated, however, that the 

 isoelectric point appeared to lie between pH. 5.5 and 6.0. The pH 

 of suspensions of this edestin in distilled water was found to be 5.0. 



n. 



Titration of Edestin with Acids and Bases. 



Titration curves of solutions of edestin in acids and bases were 

 obtained in the region where 0.45 gm. could be almost completely 

 dissolved in 100 cc; i.e., below pH 5.0 and above pH 9.0. Solutions 

 were prepared containing different quantities of acid or alkali but of 

 the same concentration with respect to edestin, and the pH values were 



^Rona, P., and Michaelis, L., Biochem. Z., 1910, xxviii, 193. The edestin used by 

 Rona and Michaelis was apparently a different substance from the present prepa- 

 ration, since they stated that only a small fraction of 1 per cent was soluble in 

 0.1 N H3PO4, whUe the edestin used in this investigation was completely soluble to 

 the extent of 1 per cent or more in 0.1 N H3PO4. 



®See also Michaelis, L., and Mendelssohn, A., Biochem. Z., 1914, kv, 1. Using 

 acetate buffers they obtained a value of 2.5 X 10"® (pH 5.60) for the isoelectric 

 point of a different edestin preparation. 



