Useful Rules and Tests. 261 



(2) S = Jl- + .2 f, S = -^ + -2 (4.2) 



4 4 



32 ^ 4 = 8, .2 (4.2) = .84, 8 + .84 = 8.84 = solids not fat. 

 8.84 4- 4.2 = 13.04 = total solids. 



(3) T = A + ^ + .14, T = -^ + liiil + .14 



4 5 4 5 



32 ^ 4 = 8, 6 X 4.2 = 25.2 ^- 5 = 5.04. 

 8 -f 5.04 + .14 = 13.18 = total solids. 



Litmus Test. 

 A method of determining whether a liquid is acid or alkaline. 

 In acid solutions, blue litmus turns red.* 

 In alkaline solutions, red litmus turns blue. 



Phenolphthalein Test. 



A method of determining whether a liquid is acid or alkaline. 



In acid solutions, if phenolphthalein is added no change in color 

 is produced. 



In alkaline solutions, if phenolphthalein is added the liquid turns 

 pink. 



To Determine the Percentage of Lactic Acid in Milk by the 

 Use op Decinormal Alkali, or Farrington's Alkaline Tablets. 



Each c. c. decinormal alkali neutralizes .009 grams lactic acid. 

 Therefore, multiply the number of c. c. decinormal alkali used by 

 .009 and divide the product by the number of grams of milk taken. 

 (Grams = c. c. X 1.032); e. g.: 20 c. c. of milk require 9 c. c. deci- 

 normal alkali to neutralize the acid. The per cent of acid is — 



.009 X 9 = .081 grams lactic acid. 



.081 ^ 20.64 = .0039, or .39 %. 



Each alkaline tablet = 3.8 c. c. decinormal alkali. Each tablet 

 is dissolved in 10 c. c. water. Each c. c. tablet solution = .38 

 c. c. decinormal alkali. Therefore, each c. c. tablet solution will 

 neutralize .009 X .38 = .0034 grams lactic acid. Therefore, mul- 

 tiply the number of c. c. of tablet solution used by .0034 and 

 divide by the number of grams of milk taken (grams = c. c. X 

 1.032); e. g.: 



20 c. c, of cream require 35 c. c. of tablet solution to neutralize 

 the acid. The per cent of acid is — 



.0034 X 35 = .119 grams lactic acid. 



■119 -- 20.64 = .0058, or .58%. 



