,3'>() IiKi'oiM- OF iiiK Department of Chemisikv of the 



The amount of acid required to precipitate completely the para- 

 casein in these compounds is exactly equal to the alkali used to 

 dissolve the paracasein; this indicates that there is no additional 

 paracaseinate, in insoluble form, containing less of these basic 

 elements. 



Preparation of mono-ammonium paracaseinate. — This compound 

 was isolated and prepared in dry form, for futher study, in the 

 manner already described in the preparation of mono-ammonium 

 caseinate (p. 320). Care must be taken to use a paracasein prepa- 

 ration free from casein or salts of calcium, strontium, barium, etc. 

 A determination of the amount of ammonia present in preparations 

 thus made is given below. 



Table XI. — Composition of Mono-A.mmonium Par.'ICaseinate. 



Amount 

 of para- 

 caseinate 

 used. 



Grams. 

 4 

 4 



Amount of 

 L NH4OH 

 1" found. 



Cc. 



8.20 

 7.98 



Relation of paracasein to NHiOH in paracaseinate. 



I gram of paracasein to 2.05 x 10^ gram equivalents 

 1 " " " 2.00 X 10-^ " " 



Percent- 

 age of 

 NH4 in 

 para- 

 caseinate. 



0.37 

 0.36 



These results show the difficulty of making a pure compound, but 

 they indicate that the percentage of ammonium is double that found 

 in the corresponding mono-ammonium caseinate. 



Acid paracaseinates of calcium, strontium and barium. — In pre- 

 paring paracasein salts of calcium, strontium and barium, the pres- 

 ence of their chlorides causes much more trouble in respect to pre- 

 cipitation than in case of the casein salts. Special care must be 

 taken to prevent the accumulation of chlorides of these elements. 

 By sufficiently frequent dialysis it was possible to obtain the results 

 reported below (Table XIII). Another point in connection with 

 paracasein is the fact of its slow rate of solution in the hydroxides 

 of calcium, strontium and barium; on this account we used 400 cc. 

 of ^ hydroxide to dissolve 5 grams of paracasein, making the volume 

 up to 500 cc. with water. 



Trial or preliminary determinations were made in the same manner 

 as with casein (p. 321), in order to determine the amount of ^ HCl 

 required to precipitate the paracasein in the absence of chlorides of 

 calcium, strontium and barium. The specific details employed and 

 results obtained are indicated in the following table; 



