112 MILK PRODUCTS 



mined by evaporation as described on page 13. 

 Acidity is determined by titration with ^/^^ 

 alkali, using phenolphthalein or methyl-orange as 

 an indicator. The amount of acidity is expressed 

 in terms of lactic acid. The Kjeldahl-Gunning 

 method will give the total nitrogen. For further 

 examination of the nitrogenous bodies, the 

 methods given on pages 106 to 108 may be applied. 

 Total redudng carbohydrates may be estimated 

 as given on page 32. If sucrose and common 

 yeast have been added, the fermented material 

 wiU be likely to contain invert-sugar, with un- 

 changed lactose and sucrose, and the method of 

 examination of sweetened condensed milk may 

 be appHcable. Pat can, probably in all cases, 

 be determined with sufficient accuracy by the 

 L-B. process. If it be desired to make polari- 

 metric readings, the liquid should be clarified 

 with acid mercuric nitrate solution (page 37), as 

 some partly hydrolyzed proteins which have 

 rotatory power may not be precipitated by other 

 reagents. The determination of alcohol accu- 

 rately is difficult, as the quantity is usually 

 small. The cautious distillation of a consider- 

 able volume of the material previously neutral- 

 ized with a little sodium hydroxid will yield 

 a distillate in which alcohol may be detected 

 and determined by the usual methods. 



