284 Report of the Department of Chemistry of the 



cipitation is next determined, and about one-third of this amount 

 is added to the solution. The mixture is then filtered to remove 

 any precipitate that is formed and the filtrate is dialyzed to remove 

 magnesium chloride as completely as possible. This solution, con- 

 taining di-magnesium caseinate, is divided into two portions, one 

 being used for the preparation of di-magnesium caseinate and the 

 other for the preparation of mono-magnesium caseinate. 



To one portion of the solution acid-free alcohol is added and a 

 precipitate of di-magnesium caseinate obtained. This is thoroughly 

 washed with acid-free alcohol and ether and dried at 120° C. 



Determination of the magnesium in this preparation showed it 

 to contain 0.24 per ct. Mg (equal to 0.40 per ct. MgO). Calculated 

 to correspond with di-calcium caseinate (containing 0.44 per ct. 

 Ca or 0.62 per ct. CaO), this caseinate should contain 0.26 per ct. 

 Mg (equal to 0.44 per ct. MgO). Expressed in another form, our 

 results indicate that 1 gram of casein combined with 2.14 x 10- 4 

 gram equivalents of magnesium (theoretical, 2.25 x 10- 4 ). 



Di-magnesium caseinate is slightly soluble in water; it is soluble 

 in a 5 per ct. solution of NaGl at 65° C. and at this temperature is 

 slightly sticky. 



PREPARATION AND COMPOSITION OF MONO-MAGNESIUM CASEINATE. 



In preparing mono-magnesium caseinate, the remaining portion 

 of the solution of di-magnesium caseinate was treated with enough 

 acid to precipitate three-fourths of the casein, the acid being added 

 very slowly and with constant, vigorous agitation. The solution 

 was filtered and the precipitated caseinate washed with water, 

 alcohol and ether, after which it was dried for three days in vacuo 

 over sulphuric acid. 



Determination of magnesium gave 0.13 per ct. Mg (equal to 0.22 

 per ct. MgO) . Calculated to correspond with mono-calcium caseinate 

 (0.22 per ct. Ca or 0.31 per ct. CaO), this compound should con- 

 tain 0.13 per ct. Mg (equal to 0.22 per ct. MgO). Expressed in 

 another form, our results show that 1 gram of casein combines with 

 1.125 x 10- 4 gram 'equivalents of magnesium, which agrees with 

 the theoretical value. 



Mono-magnesium caseinate is insoluble in water, but soluble in 

 5 per ct. NaCl solution; at 65° C. it shows a tendency to form strings 

 when drawn out. 



VALENCY OF CASEIN. 



In Technical Bulletin No. 26, Van Slyke and Bosworth have 

 shown from their work with calcium casemates the combining power 

 of casein in the different compounds prepared and studied by them. 

 It is interesting to compare their results with those obtained with 

 magnesium. In the following table we arrange the results ex- 



