110 Testing Milk and Its Products. 



by Soxhlet and Henkel has since been in general use by 

 European chemists. They measured out 50 cc. of milk 

 ta which was added 2 cc. of a 2 percent, alcoholic solu- 

 tion of phenolphtalein, and this was titrated with a one- 

 fourth normal soda solution 1 (see below). In this country, 

 Dr. A. G. Manns in 1890 published the results of work 

 done in the line of testing the acidity of milk and 

 cream, 2 and the method of procedure and apparatus 

 proposed by him has become known under the name of 

 Manns' test, and has been advertised as such by dealers 

 in dairy supplies. 



128. Manns' test. The acid in milk or cream is meas- 

 ured by using an alkali solution of a certain strength, 

 with an indicator which shows by a change of color in 

 the milk when all its acid has been neutralized. Any 

 of the alkalies, soda, potash, ammonia, lime or barium 

 can be used for making the standard solution, but it 

 requires the skill and apparatus of a chemist to prepare it 

 of the proper strength. A one-tenth normal solution 3 of 

 caustic soda is the alkali solution used most frequently 

 in determining the acidity of milk, and is the solution 

 labeled Neutralizer of the Manns' test. 



1 Fleischmann, Lehrb. d. Milch wirtschaft, p. 126. 



2 Illinois experiment station, bulletin No. 9. 



3 Normal solutions, as a general rule, are prepared so that one liter 

 shall contain the hydrogen equivalent of the active reagent weighed in 

 grams (Button). Caustic soda (Na. OH.) is made up of an atom each of 

 sodium (Na), oxygen (O), and hydrogen (H); its molecular weight is 

 therefore 



23 + 16 + 1 = 40 



Na O H 



A normal soda solution then is made by dissolving 40 grams of soda in 

 water, making up the volume to 1000 cc.; a one-tenth normal solution will 

 contain one-tenth of this amount of soda, or 4 grams dissolved in one liter. 

 One cubic centimeter of the latter solution will contain .004 grams of soda, 

 and will neutralize .009 grams of lactic acid. The formula for lactic acid is 

 C 3 H 6 O 3 (see page>16), and its molecular weight therefore 3x12+6x1+3x16 

 =90. A one-tenth normal solution of lactic acid contains 9 grams per liter, 

 and .009 grams per cubic centimeter. 



