ACIDITY TESTS. 39 



The acidity in the cream would be 30X018 or .54 

 per cent, or 



30 X. 009 



X100=.54 per cent. 



50 



44. Suppose a 17.6 c.c. pipette is used, requiring 

 10 c.c. of solution to neutralize the acidity, the fac- 

 tor which is found as follows (.009-=-17.6)XlOO= 

 .051 and the acidity of the cream would be found by 

 multiplying the factor by 10, or .051X10=.51 per 

 cent. 



17.6 



Acidity of cream= Xl00=.51 per cent, or 



10 X -009 



Acidity of cream=.05lX 10^.51 per cent, or for 

 practical purposes the acidity may be found by di- 

 viding 10 c.c. by 2, giving the acidity of .50 per cent. 

 The factor which corresponds with each size of pi- 

 pette is to be multiplied by the number of c.c. of 

 solution used to neutralize each sample. The result 

 is the acidity in per cent. These calculations are 

 based upon a one-tenth normal solution. The figure 

 .009 is the number of c.c. of lactic acid neutralized 

 by one c.c. of the solution used. As a rule when 

 Mann's acid test is used, a 50 c.c. pipette is used. 

 Those who are accustomed to the use of the 50 c.c. 

 pipette usually give the number of c.c. of solution 

 used, from the burette, and not the per cent of acid- 

 ity in the milk or cream. Acidity should, however, 

 be expressed in per cent, as this is the only logical 

 and reasonable method of expressing it. If the so- 

 lution weakens from age before it is all used, a fresh 

 solution of standard strength should be procured. 



