New YorK AGRICULTURAL EXPERIMENT STATION. 165 
a test for it in any cheese examined by us. The behavior of 
indicators toward the water-extract of cheese is not such as free 
lactic acid would give. 
In the discussion given in the preceding pages, it has been 
stated that the lactic acid formed during and after the cheese- 
making process combined with a portion of the calcium of the 
insoluble calcium phosphate present, forming mono-calcium 
phosphate and calcium lactate. The power of the water-extract 
of cheese to neutralize alkali appears to be largely due to the 
mono-calcium phosphate present and may, of course, be regarded 
as an indirect measure of the amount of lactic acid that has 
combined with calcium and remains in cheese. The different 
substances present in the water-extract of cheese that might be 
thought to influence appreciably the determination of acidity 
by titration with alkali are mono-calcium phosphate, calcium 
lactate and soluble proteid. While, as shown later, we know 
that all the calcium lactate of cheese appears in the water- 
extract, this salt is neutral and has no effect upon indicators. 
The amount of soluble proteid is for some time insufficient to 
account for any appreciable amount of acidity. Therefore, the 
only compound present in amounts that can account for any 
considerable part of the neutralizing property of the water- 
extract of cheddar cheese in its early history is mono-calcium 
phosphate. The behavior of the water-extract of cheese with 
indicators harmonizes with this statement. Thus, it is acid to 
phenolphthalein, neutral or very slightly alkaline to congo red, 
to cochineal and to litmus, and alkaline to methyl orange. 
We have used the following modification of the official method 
for determining acidity in cheese and we believe that it ‘gives 
more satisfactory results: Extract 25 grams of finely divided 
cheese with 200 c. c. of water at 50° C., decant the supernatant 
liquid on a filter of absorbent cotton and repeat the treatment 
with the residue until nearly a liter of extract is obtained. 
Make up to one liter and mix thoroughly. Of this solution take 
100 c. c. for titration with N-2o0 solution of sodium hydroxide, 
using phenolphthalein as indicator. The result multiplied by 
20 gives the number of cubic centimeters of N-to-alkali required 
to neutralize the water-extract from t00 grams of cheese, and 
this appears to be a desirable form in which to express the 
results of acidity determinations. 
We have already referred to the fact that we made determina- 
tions showing that all the calcium lactate of cheese is removed 
