II2 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 reducing carbohydrates may be estimated 
as given on page 32. If sucrose and common 
yeast have been added, the fermented material 
will be likely to contain invert-sugar, with un- 
changed lactose and sucrose, and the method of 
examination of sweetened condensed milk may 
be applicable. Fat 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. 
