596 TESTING MII^K AND CREAM FOR ACID 



be constructed of reasonably thin glass, the ordinary test tubes used 

 in the chemical laboratory are very suitable for this purpose. They 

 should have an outside diameter of % inch and should be about 7 

 inches long, so that they readily slip through the mouth of the two- 

 gallon bottle. 



Seal these tubes by fusing the glass over the flame. In order to 

 make up a tenth normal solution, all the operator has to do is to 

 drop one of these tubes rilled with dry sodium hydroxide into the 

 two-gallon bottle. The tube breaks as it strikes the bottom of the 

 bottle, releasing the alkali. Now fill the bottle with water to the 

 scratch on the shoulder. Mix thoroughly by placing hand over 

 mouth of bottle and inverting it several times, until the alkali is all 

 dissolved. This is now a tenth normal solution which is ready for 

 use. 



When the solution has been used up, empty the bottle of the 

 remnant of solution and the broken glass tube, drop into the bottle 

 a fresh tube and again fill up with distilled water and mix. 



If commercial sodium sticks are used, which are not chemically 

 pure, from 31 to 32 grams are required, according to the extent of 

 impurities present. In this case the sodium hydrate should be care- 

 fully titrated against standard acid, so as to determine the exact 

 amount of sodium hydrate to be weighed into the glass tubes that 

 will yield, in the 7500 c.c. of distilled water, a tenth normal solution. 



Calculation of Per Cent Acid When a Tenth Normal Solution 

 of Sodium Hydroxide is Used 



1 c.c. ^ NaOH neutralizes 1 c.c. ^ C 3 H 6 O 3 . 



N 

 1 c.c. of a -r:r lactic acid solution contains .009 grams lactic 



i J. \J 



acid. 



Hence, in order to find the per cent acid in milk, cream or 

 starter, multiply the cubic centimeters of alkali solution required to 

 neutralize the milk or cream with .009, divide the product by the 

 grams of milk or cream used and multiply by 100. 



N 

 c.c. alkali solution X .009 



X 100 = % lactic acid. 



grams milk or cream .ME .1 



For all practical purposes the measuring of the milk or cream 

 gives sufficiently accurate results to obviate the less practical and 



