Xew York Agricultural Experiment Station. 333 



Preparation of mono- and di-calcium paracaseinates. — In order to 

 study the composition and properties of these compounds further, 

 preparations of the mono- and di-calcium paracaseinates were made. 

 The first steps in making these compounds are the same. An excess 

 of ash-free paracasein is agitated with Ume-water until a saturated 

 solution is formed, the undissolved paracasein being removed by 

 filtration. To the solution to HCl is added until a permanent pre- 

 cipitate begins to appear. The solution is again filtered and then 

 dialyzed. Alternate addition of acid and dialysis are continued 

 until no more acid can be added after dialysis without causing 

 precipitation. The amount of ^ HCl required to precipitate all 

 the paracasein is next determined in an aliquot portion, and one- 

 third that amount of acid is added. The solution is then filtered 

 and dialyzed. This solution contains di-calcium paracaseinate. 

 This solution is divided into two portions; in one the di-calcium 

 paracaseinate is precipitated by addition of acid-free alcohol, the 

 precipitate being washed with acid-free alcohol and ether and dried 

 at 120° C. This preparation was found to contain between 4.2 x 10* 

 and 4.6 X 10* gram equivalents of calcium for 1 gram of paracasein. 



In the second portion of di-calcium paracaseinate solution, enough 

 § HCl is very slowly added to precipitate three-fourths of the para- 

 casein in solution. The precipitate is mono-calcium paracaseinate; 

 this is filtered, washed with acid-free alcohol and ether, and dried 

 at 120° C. Before being washed with alcohol, the precipitate is 

 completely soluble in 5 per ct. solution of sodium chloride. This 

 compound, mono-calcium paracaseinate, is identical in its properties 

 with the brine-soluble compound formed in cheddar cheese, to which 

 attention was first called by Van Slyke and Hart under the expres- 

 sion, " salt-soluble compound." Attention will again be called to 

 this compound later. An analysis of this preparation showed it to 

 contain between 2x 10* and 2.3 x 10* gram equivalents of calcium 

 for 1 gram of paracasein. 



VALENCY OF PARACASEIN MOLECULE AND MOLECULAR WEIGHT OF 



PARACASEIN. 



In the case of basic calcium paracaseinate, the compound that is 

 neutral to phenolphthalein, it is found that 1 gram combines with 

 9 X 10* gram equivalents of calcium, while in the case of mono- 

 ammonium paracaseinate the combination is in the ratio of 1 gram 

 of paracasein to a value between 2.2x10* and 2.3x10* gram 

 equivalents. According to the rule of constant proportions, the 

 number of valencies satisfied in the first compound would be between 

 ^2 and ^ or 4. The molecular weight of paracasein would 

 therefore be 2:2-5^-1-0"* or 4444+. Our results indicate that the 

 molecular weight of casein. 8888, is just twice that of paracasein 

 4444. Using the sulphur content as a basis for calculating the 

 molecular weight of paracasein, we have n(-§;fj) 100 = n 4454-[-. 



