304 THE CHEMISTRY OF DAIRYING 



of the presence of citric acid (in the form of salts) as a normal 

 constituent of milk to the extent of about 0*15 per cent. 



Soldner has worked out the probable combinations of the 

 various constituents of the ash in the original milk, and gives 

 the result as follows : 



Per cent. 



Sodium chloride (NaCl) icr62 



Potassium chloride (KC1) . ;.-. "'..-, . . . . 9*16 



Potassium dihydrogen phosphate (KH 2 PO 4 ) . 12*77 



Dipotassium hydrogen phosphate (K 2 HPO 4 ) 9*22 



Potassium citrate (K 3 Ci) . . ... . . 5*47 



Magnesium hydrogen phosphate (MgHPO 4 ) . 3*71 



Magnesium citrate (Mg 3 Ci 2 ) 4'5 



Calcium hydrogen phosphate (CaHP0 4 ) . . 7*42 



Tri-calcic phosphate {Ca 3 (PO 4 ) 2 } .... 8-90 



Calcium citrate (Ca 3 Ci 2 ) . . ....- . . 23-55 



Calcium oxide combined with casein . . . 5*13 



lOO'OOO 



If it be true that milk contains dicalcic and tricalcic phos- 

 phates, these substances must be present in a state of suspension, 

 as they are not soluble in water ; and, according to Soldner's 

 estimate, they form, together, from 36 to 56 per cent, of the 

 total phosphoricanhydride, and from 53 to 72 per cent, of the 

 total calcium oxide present in the milk. 



When milk is freshly drawn, it exhibits the so-called 

 amphoteric reaction, i.e. it turns blue litmus paper red (acid 

 reaction), and it also turns turmeric paper brown (alkaline 

 reaction). This phenomenon should, however, be regarded as 

 a question of the chemistry of the indicators rather than as one 

 of the chemistry of milk. Magnesium hydrogen phosphate 

 when moistened with dilute hydrochloric acid produces similar 

 effects. The amphoteric reaction of milk has been attributed 

 to the presence of this and other acid (primary and secondary) 

 phosphates. The amphoteric reaction soon disappears owing 

 to the formation of carbon dioxide, and the milk eventually 

 becomes distinctly acid. 



