^^ CONSTITUENTS OF MILK 



Caseinogen, when dissolved in dilute alkali, has a pronounced 

 tevo rotatory action on polarized light, but the specific rota- 

 tion is not constant, vaiying from -94.8 to -111.8, according 

 o the concentration and nature of the alkali used a. the solvent 

 (Long). The soluble salts of caseinogen may be divided into 

 two classes (1) salts of the alkaline earths, and (2) salts of the 

 alkahes According to Osborne Uhese are distinguished by 

 the mabihty of the fomer to pass through the film of the 

 Martm gelatin filter and by the formation of opalescent solu- 

 tions The solutions of the second class filter through gelatin 

 membranes and are translucent. Both classes of salts are 

 neutral to phenolphthalein when the valency of caseinogen is 

 entirely satisfied, but when litmus is used as the indicator no 

 defimte change is indicated and the point of neutrahsation 

 varies with the concentration of the solution (Schiyver) 

 Sa^ts of copper, mercury, and lead, precipitate caseinogen 

 from neutral solutions, and mercuiy salts are also effective in the 

 presence of acid: the precipitates so obtained are not constant 

 m composition but vary with the conditions obtaining The 

 msolubihty of the compounds with the heavy metals is utilised 

 m milk analysis in the preparation of protein free milk serum 

 for use in the polarimeter and refractometer. Caseinogen also 

 exhibits basic properties and combines with acids with the 

 formation of clear solutions. Long« found that 1 gram of 

 caseinogen combined with about 7 c.cms. of ^ acid in the form 

 of sulphuric, hydrochloric, hydrobromic, hydriodic, and acetic 

 acids to form soluble salt Uke compounds. Some observers 

 have stated that precipitated caseinogen also combined with 

 acids but L. L. Van Slyke and D. D. Van Slyke« have shown 

 that the observed loss of acid on precipitation was due to sur- 

 face adsorption and depended upon the nature and concen- 

 tration of the acid, the temperature, the duration of contact, 

 and the degree of agitation. 



