HARPER F. ZOLLER 651 



with the MacMichael instrument from 71.0 before pasteurizing to 

 69.0 after pasteurization. When the casein is separated from the 

 milk serum salts and dried, its hydrophyllic properties are changed 

 and it can then imbibe more water. Inasmuch as borate solutions 

 buffer in the region of maximum viscosity of casein solutions it is 

 peculiarly well suited to the differentiation of heated and unheated 

 caseins, from the standpoint of their power of imbibition. 



Fig. 5 shows the viscosity-pH curves of two caseins; one of a casein 

 prepared without heat treatment, the other of some of the same casein 

 precipitated from NaOH solution (pH 7.2) after the solution had 

 been boiled for 20 minutes; the casein was dried with alcohol. The 

 viscosity of the heated casein is nearly twice that of the unheated. 

 The conditions of measurements were the same and the solvent was 

 m/1 NaOH. 



SUMMARY. 



1. Viscosity and pH curves of casein dissolved in NaOH, KOH, 

 LiOH, and NH4OH are shown and it is found that a maximum vis- 

 cosity occurs at about the same pH point with each alkali; i,e., 9.1 to 

 9.25. The magnitude of the viscosity is largest in ammonia solutions. 



2. The maximum viscosity occurs in 8 to 10 per cent solutions of 

 casein in alkalies when about 98 X 10~^ gram equivalents of base are 

 combined with 1 gram of casein. 



3. A maximum viscosity occurs in the same region (pH 9.1 to 

 9.25) when casein is dissolved in Na2C03, Na3As04, Na2S03, NaF, 

 and Na2P03. 



4. The maximum viscosity obtained with borax solutions of casein 

 occurs at 8.15 to 8.2 pH. It is suggested that casein acts like man- 

 nitol, glycerol, etc., in increasing the dissociation of boric acid. 



5. The flattening of the viscosity curves of casein solutions, fol- 

 lowing the decline from maximum, is shown to be due to alkaline 

 hydrolysis whence casein no longer exists as such but is cleaved into 

 a major protein containing no phosphorus or sulfur and less nitrogen. 

 This cleavage commences at pH 10.0 to 10.5. 



6. When casein is prepared from solutions that have been sub- 

 jected to high temperatures (60°C. and above) or has otherwise been 

 heated during its preparation, it yields solutions in alkalies of high 

 viscosity. 



