310 Repoet of the Department of Chemistry op the 



(4) Acid or unsaturated casemates of ammonium, sodium and 

 potassium. — These compounds were prepared as follows : Ash-free 

 casein is dissolved in alkaU so that 50 cc. of ^ alkali contain i gram 

 of casein. This is neutralized with ~ HCl, which is added in 

 small portions, under constant agitation, until a permanent precipi- 

 tate begins to appear, as shown by centrifuging a portion of the 

 mixture in a sedimentation tube. This method enables one to 

 detect the casein precipitated by 0.20 cc. of ^ HCl. The point at 

 which a permanent precipitate first begins to appear is noted and 

 addition of acid is continued until all the casein is precipitated, 

 which point is also noted. Three different casein preparations were 

 used and numerous determinations were made. It was found that 

 I gram of casein forms a soluble compound with each of the alkalis 

 used when combined with amounts somewhere between i.io x 10^ 

 and 1. 15 X 10^ gram equivalents of alkali; or, i cc. of ^ alkali 

 combines with an amount of casein somewhere between 0.87 and 

 0.91 gram. The proportion of basic element in each compound is 

 as follows: NH4, 0.20 per ct.; Na, 0.26 per ct.; and K, 0.44 per ct. 

 Such casein compounds contain the smallest known amount of base 

 and it is suggested that they be called mono-basic caseinates. 



Special preparations were made of mono-ammonium caseinate, 

 the compound being isolated and prepared in dry form. This was 

 found to have the composition called for by the previous results 

 obtained with the volumetric work. 



(5) Acid or unsaturated caseinates of calcium, strontium and 

 barium. — When a solution of casein in a hydroxide of calcium, etc., 

 is treated with an acid, the caseinate is precipitated by the chloride 

 formed; this difficulty can be overcome by removal of the chloride 

 through simple dialysis before the amount is sufficient to cause 

 precipitation. One gram of ash-free casein is dissolved in 250 cc. 

 of ~ hydroxide solution and I, HCl is added until the first sign 

 of a permanent precipitate appears, as shown by centrifuging a 

 portion. The solution is then dialyzed to remove soluble chloride 

 and then acid is again added until precipitation again occurs and 

 another dialysis is made. Alternate addition of acid and dialysis 

 are continued until fiinally the dialyzed solution forms a permanent 

 precipitate with the addition of any acid. The results of many 

 experiments agree in indicating the formation of two sets of com- 

 pounds, mono-basic and di-basic, one set containing twice as much 

 base as the other. In the di-basic compounds, i gram of casein 

 requires between 2.2 x lo'^ and 2.3 x 10^ gram equivalents of 

 hydroxide to form a compound soluble in water but easily precipi- 

 table by even a small amount of a soluble chloride of calciimi, 

 strontium or barium. In the di-basic compounds, i gram of casein 

 combines (a) with 0.44 to 0.46 gram Ca (0.62 to 0.64 CaO), (b) with 

 0.96 to i.oi gram Sr (1.14 to 1.19 SrO), and (c) with 1.51 to 1.58 

 grams Ba (1.69 to 1.76 BaO). In the mono-basic salts, i gram of 



