IJASEIX. 31 



above formula to replace the atom of sodium by hydrogeu in 

 the above formula is 8-3 c.c. The precipitated casein contained 

 all the lime and phosphoric acid, the quantities carried down 

 being (calculated as before for 0-477 nitrogen) — 



CaO, U-120 



PaOr,, . ()-12U 



Total ash, . . . . i)-23 



From the above figures it is seen that the formula given fairly 

 well represents the composition of casein, though, of course, it 

 is only an approximation ; the real formula is almost certainly 

 a multiple of this. 



It is noticed that the sulphur is lower than that calculated 

 from either of the above formulfe. By treating casein with 

 alkalies a portion of the sulphur is removed as sulphide. It is 

 possible that in the purification of the casein by solution in 

 dilute alkali and precipitation by acids that n snuill amount of 

 decomposition sets in. 



The following are the amounts of various acids (calculated as 

 c.c. of normal solution per litre of milk) required to piciipitate 

 the casein on boilinij; : — 



That large amounts of the weaker acids are required is only 

 to he expected ; the behaviour of oxalic and pho-;phoric aeids is 

 anomalous, and appears to be due to the fact that oxalic acid 

 removes the lime from the cusL'in complex, while phosphoric 

 acid forms an acitl phosphate with the tricalcium pliosphate. 

 In eithei- case the formation of a mono-acid calcium salt of casein 

 combined with calcium phosphate is prevented. 



Revis and Payne consider that casein exists in milk com- 

 bined with calcium phosphate, and that on acidifying the milk 

 with small progressive amounts of acid the calcium phosphate 

 is removed from the combination ; when the casein is precipi- 

 t4itcd by the acid practically all the calcium phosphate is pre- 

 cipitated. Their results show that calcium is removed from the 

 complex in direct proportion to the acid added, but their figures 

 with j'egard to phosphoric acid are less definite. 



They also show that it is very improbable that any appreciable 

 amount of lactates of casein are formed in milk as it turns sour, 

 as supposed by van Slyke, Hart, and Laxa. 



Casein behaves. as a tribasic acid ; it has also basic properties, 

 and combines with acids giving salts easily decomposed by water. 

 The acid functions are much more strongly marked than the 



