10 CONSTITUENTS OF MILK 



octobasic. This would give a molecular weight of approxi- 

 mately 8900. 



Caseinogen, when dissolved in dilute alkali, has a pronounced 

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

 tion is not constant, varying from 94.8 to 111.8, according 

 to the concentration and nature of the alkali used as 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 

 alkalies. According to Osborne 7 these are distinguished by 

 the inability of the former to pass through the film of the 

 Martin 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 

 definite change is indicated and the point of neutralisation 

 varies with the concentration of the solution (Schryver). 

 Salts of copper, mercury, and lead, precipitate caseinogen 

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

 presence of acid: the precipitates so obtained are not constant 

 in composition but vary with the conditions obtaining. The 

 insolubility of the compounds with the heavy metals is utilised 

 in 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 8 found that 1 gram of 



N 

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



of sulphuric, hydrochloric, hydrobromic, hydriodic, and acetic 

 acids to form soluble salt like compounds. Some observers 

 have stated that precipitated caseinogen also combined with 

 acids but L. L. Van Slyke and D. D. Van Slyke 9 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. 



