442 SCIENCE AND PRACTICE OF CHEESE-MAKING 



(2) Acetic acid. — This solution is so made that a 

 given amount of it will exactly neutralize the same 

 amount of the standard alkali solution of the strength 

 above indicated. The simplest way of preparing this 

 solution is to purchase a normal solution and dilute 

 100 cc. of this to 1,260 cc. To prevent fermentation of 

 dilute acetic acid and consequent change of strength on 

 long standing, it is desirable to add a small amount of 

 pure mercuric chlorid (corrosive sublimate) and to 

 keep the solution in tightly-stoppered bottles. 



(3) Phenolphthalein solution. — This is made by 

 dissolving one gram of the dry, powdered compound in 

 100 cc. of 50 per cent alcohol and adding to the pre- 

 pared solution one or more drops of dilute alkali until 

 the solution is very slightly pinkish in color. 



Performing the test. — (i) Measuring and diluting 

 sample of milk. The milk to be tested is well mixed 

 and a 17.6 cc. pipette filled to the mark and the milk 

 run into a 200 cc. flask. Then add about 80 cc. of 

 pure, soft water (preferably, distilled). 



(2) Neutralizing the milk. — Add i cc. of phenol- 

 phthalein solution to the dilute milk and then run into it 

 the alkali solution from a burette, in small portions, 

 shaking vigorously after each addition of alkali, until 

 a faintly, but distinctly, pinkish shade of color remains 

 even after considerable agitation. Marked excess of 

 alkali must be avoided. 



(a) Preparation of a color-standard. — More satis- 

 factory results in neutralizing can be obtained by pre- 

 paring a color-standard for comparison. This can be 

 prepared as follows : About 20 cc. of fresh skim-milk 

 and 80 cc. of water are put into a 200 cc. flask and a 

 very small amount of pure corrosive sublimate added 

 to prevent souring. A few drops of ordinary carmine 



