448 MILK AND MILK PRODUCTS; DAIRY FARMS 



slowly adding to a known weight of milk an alkali of known strength 

 until all the acid is neutralized. The neutralization is indicated by 

 phenolphthalein, which was previously added to the milk and which 

 causes the milk to turn pink as soon as it begins to show an alkaline 

 reaction. It is customary (Mann's test) to use deci-normal alkali 

 solution, 1 cc. of which will neutralize .009 gram of lactic acid. The 

 equipment includes, besides the neutralizer and phenolphthalein, a 

 burette for measuring the neutralizer, cup and glass rod. If twenty 

 grams of milk is used and it requires 6 cc. of alkali to neutralize the 

 acid, it is known that the milk contains 6X.009 or .054 gram of lactic 

 acid, or .27 per cent. Alkali tablets (Farrington's), each capable of 

 neutralizing .034 gram of acid, are on the market. They may be 

 used in solution instead of the deci-normal solution. 



Test for boiled milk. 



It is sometimes desirable to determine whether milk has been sub- 

 jected to 176 F. or higher heat. A successful test has been devised 

 by Storch. To 5 cc. of the suspected milk add a few drops of potassium 

 iodid and a similar quantity of starch solution, also a- few drops of 

 hydrogen peroxid. If the milk has not been cooked, an enzyme which 

 is present will decompose the hydrogen peroxid, setting free oxygen. 

 This combines with the potassium salt, and thus iodine is in turn set 

 free and with the starch it forms a purple color. If the milk has been 

 heated so that the enzyme is killed, no color will result. 



Another test for cooked milk is given by Arnold, as follows : Tincture 

 of guaiac is added, drop by drop, to a little milk in a test-tube. If the 

 milk has not been heated to 176 F., a blue zone is formed between 

 the two fluids. If it has been heated, there is no reaction. The guaiac- 

 wood tincture is said to be more reliable than other tinctures, and it 

 should not be used when fresh, but when at least a few days old and its 

 potency has been determined. 



The lactometer test for specific gravity in milk (Pearson). 



As the specific gravity of milk is markedly changed when it is adul- 

 terated by the addition of water or the removal of cream, the lactometer 

 is an important instrument to indicate such adulteration. It is of 

 little use if both kinds of adulteration have been practiced on the 

 same sample of milk, as the increase in weight due to removal of 

 cream can be offset by the addition of water, which is lighter than 



