29 



FIFTH LECTURE. 

 OTHER JESTS USED IN CONNECTION WITH CHEESE MAKING. 



In addition to (ieterminino; fat there are some other forms of tests 

 of vahie in connection with cheese making;, and some of these will be 

 considered here. 



1 . Use of lactometer in determining solids of milk. — The specific grav- 

 ity of milk is the weiji^ht of a given bnlk of milk as compared with the 

 weight of an equal bulk of water at the same temperature. The spe- 

 cific gravity of milk averages about 1.032. Fat, being lighter than 

 water, decreases specific gravit}^, while such compounds as casein and 

 milk sugar, being heavier than water, increase the specific gravity 

 (reference No. 3, p. 113). The specific gravity is found out by means 

 of a lactometer. Two forms are in common use, the Quevenne lac- 

 tometer (reference No. 3, p. 43) and the board of health lactometer (ref- 

 erence No. 3, p. 114). The lactometer is used as follows in determin- 

 ing solids of milk : Rule 1 . To find the per cent of total solids in milk 

 multiply the per cent of fat by 1.2 and add the result to one-fourth 

 of the lactometer (Quevenne) reading (reference No. 3, p. 114). [Ex- 

 amples should be given and actual determinations should be made 

 by the lecturer and then by each student.] 



2. Testing acidity of milk and whey. — The method of testing acidity 

 in milk or whey is based upon the chemical action taking place between 

 acids and alkalis (reference No. 3, p. 111). Acids and alkalis neutral- 

 ize each other and form compounds called salts, which are neither acid 

 nor alkaline, but neutral. An indicator is a substance used to tell 

 whether a solution is acid, alkaline, or neutral. The most common 

 indicator is phenolphthalein, which turns pink in alkali solutions and 

 colorless in acid or neutral solutions. For use, 1 gram of phenolphtha- 

 lein is dissolved in 50 cubic centimeters of strong alcohol and 50 cubic 

 centimeters of water. Only a few drops need be used (reference No. 3, 

 p. 111). The two forms of acid test in common use are those devised 

 by Mann and by Farrington. 



(a) Mami's acid test (reference No. 3, p. 112, or No. 12, p. 96). 

 Measure just 50 cubic centimeters of milk or whey into a clean porce- 

 lain cup or glass. Add a few drops of phenolphthalein and then let in 

 from a burette, previously filled to zero point, a little neutralizer. 

 A pink color appears and then disappears on stirring. Add a little 

 more neutralizer and stir. Continue this until the pink color remains 

 even after considerable stirring. Look at burette and see how many 

 cubic centimeters of alkali have been used. Suppose 10 cubic centi- 

 meters of " neutralizer" have been used to neutralize the milk or whey, 

 then multiply 10 by .018 and the result is 0.18, which is the per cent of 

 lactic acid in the milk or whey. 



(6) Farrington's alkaline tablet test. In this form of test the alkali 

 and indicator (phenolphthalein) are mixed together in the form of 



