SALTS. 37 



proteins to form soluble salts, and partly with citric acid to form 

 citrates. 



Citric acid is contained in milk to the extent of 0-15 to 0-2 per 

 cent. ; its most characteristic salt is the calcium citrate, which 

 is fairly soluble in cold water, but insoluble in boiling water. 

 It is a tribasic acid, and forms three classes of salts. 



Soldner deduces the following composition as most probable 

 for the salts existing in milk : 



Per cent. 



Sodium chloride, NaCl, . . . .10-62 

 Potassium chloride, KC1, . . .9-16 



Mono -potassium phosphate, KH 2 P0 4 , 12-77 



Di-potassium phosphate, K 2 HP0 4 , 

 Potassium citrate, K 3 (C 6 H 5 7 ), . 

 Di-magnesium phosphate, MgHP0 4 , 

 Magnesium citrate, Mg 3 (C 6 H 5 7 ) 2 , 

 Di-calcium phosphate, CaHP0 4 , . 

 Tri-calcium phosphate, Ca 3 (P0 4 ) 2 , 

 Calcium citrate, Ca s (C 6 H 5 7 ).,, ". 

 Lime combined with protein, 



9-22 

 5-47 

 3-71 

 4-05 

 7-42 

 8-90 

 23-55 

 5-13 



100-00 



The mineral salts, as stated above, would amount to 0-90 per 

 cent., as against 0-75 per cent, of ash obtained. 



According to Soldner 36 to 56 per cent, of the phosphoric 

 acid and 53 to 72 per cent, of the lime are not in solution, but 

 are in the colloidal form. 



The following shows the distribution of the phosphoric acid 

 of the milk according to the author's experiments : 



P 2 5 as casein, combined with CaNa, . 0-054 per cent. 



P 3 5 as Ca 3 (P0 4 ) 2 , .... 0-066 



P 2 5 as R 2 HP0 4 , .... 0-077 



P 2 5 as R 3 P0 4 , 0-023 



Total P,0 5 , . . 0-220 



The author's conclusions differ from those of Soldner, and are : 



(i.) One-third of the base with which casein is combined in 

 milk is soda and not lime. 



(ii.) Casein forms a molecular compound with calcium phos- 

 phate. 



(iii.) The citrates are dibasic, and not tribasic. 



Other Constituents of Milk. Besides the constituents men- 

 tioned, minute traces of silica, iodine, fluorine, acetates, and 

 thio-cyanates have been described. 



None of the salts of milk require a detailed description. They, 

 together with the acids and bases composing them, are described 

 in any elementary book on chemistry. 



