CHAPTER IV. 



Acidity Tests, 



43. Mann's acidity test. The solution is prepared 

 by dissolving forty grams of caustic soda in water, 

 making a total volume of 1000 c.c. Thi.s makes the 

 normal solution. A tenth normal solution, which is 

 the strength generally used at present for testing 

 acidity, is made by dissolving four grams of caustic 

 soda in one quart of water. One c.c. of the tenth 

 normal solution contains .004 grams of soda and will 

 neutralize .009 grams of lactic acid. Mann, in his 

 directions for using this method, recommends the 

 use of a 50 c.c. pipette for measuring the cream 

 or milk. A 50 c.c, a 20 c.c, or a 17.6 c.c pipette 

 may be used. In using the different sizes of pipettes 

 factors may be used to simplify the process. These 

 factors are found by dividing .009 by the size in c.c. 

 of the pipette and multiplying the quotient by 100. 

 Factors for different sized pipettes are as follows: 



(.009-=-50) X 100=^.018 (.009-=-20) X100=.045 



(.009-=-25) X300--.036 (.009-f-17.6) Xl00=.051 



How to use the factors: U.se .018 with a 50 c.c. 

 pipette; .036 with a 25 cc. pipette; .045 with a 20 

 c.c. pipette; and .051 Avith a 17.6 cc. pipette. 



To illustrate : Suppose a 50 c.c. pipette is used in 

 taking a sample of cream, and the solution used to 

 neutralize the acidity is 30 cc, the factor is .018, 



38 



