282 Report of the Department of Chemistry of the 



5. Preparation and composition of di-magnesiwn caseinate. — To 

 the second portion of the solution mentioned in the preceding para- 

 graph acid-free alcohol is added and a precipitate obtained which 

 contained 0.24 per ct. Mg (0.40 MgO), the theoretical composition 

 of di-magnesium caseinate being 0.26 per ct. Mg (0.44 MgO); or 1 

 gram of casein combines with 2.1 x 10- 4 gram equivalent of Mg 

 (theoretical 2.25 x 10- 4 ). The compound is quite easily soluble in 

 water and in a 5 per ct. solution of NaCl; at 65 C. it is slightly sticky. 



6. These four magnesium caseinates correspond to the four calcium 

 caseinates which have been previously prepared, representing octo-, 

 penta-, di- and mono-caseinates of magnesium. 



INTRODUCTION. 



In Technical Bulletin No. 26 of this Station, Van Slyke and Bos- 

 worth report a study of compounds formed by casein with the elements 

 of several alkaline and alkaline-earth bases. In the case of calcium, 

 for illustration, it was found that at least four caseinates could be 

 formed, (1) mono-calcium caseinate, (2) di-calcium caseinate, (3) 

 neutral (or penta-valent) calcium caseinate, neutral to litmus, and (4) 

 basic (or octo-valent) calcium caseinate, neutral to phenolphthalein. 

 It seemed desirable to undertake a similar study to ascertain whether 

 casein forms corresponding compounds with magnesium. The details 

 of this work are given in this bulletin. 



DETAILS OF LABORATORY WORK. 



SOLUTION OF CASEIN IN MAGNESIUM HYDROXIDE. 



In the preparation of caseinates of the alkaline-earth elements, 

 the first step in the process is to obtain a solution of casein in the 

 hydroxide. In the case of magnesium, its hydroxide is only slightly 

 soluble in water and the solution is so dilute as to have very little 

 effect in dissolving casein. It was found, however, that when casein 

 is suspended in water with an excess of finely-divided magnesium 

 oxide and allowed to stand several days with occasional agitation, 

 enough casein is taken into solution to furnish material which can be 

 used in the preparation of magnesium caseinates. 



PREPARATION AND COMPOSITION OF BASIC MAGNESIUM CASEINATE. 



Base-free casein (prepared in the manner described in Technical 

 Bulletin No. 26, pp. 8-9) was dissolved in a solution of magnesium 

 hydroxide containing an excess of magnesium oxide in suspension. 

 The mixture was filtered and the filtrate was made neutral to phenol- 

 phthalein with hydrochloric acid; the end point was satisfactorily 

 determined by adding the acid slowly until a faintly pinkish color 

 remains for several minutes. The solution was then dialyzed to 



