Composition of Cheese. 37 



Result : The curd separated in ^ hour, but not so perfectly 

 as in the preceding experiment, and in a softer condition. 

 The whey was more milky in appearance, and strongly 

 alkaline. Examined after 24 hours' standing, it was 

 found to be neutral ; after a lapse of 2 days, it was acid. 



Even a considerable quantity of an alkali, therefore, does not 

 prevent the coagulation of milk by rennet. 



16th Exp. To another pint of milk I added an un weighed 

 quantity of potash heated to 84, and then J ounce of 

 rennet. 

 Result : No coagulation took place. 



Much more alkali was used in this experiment than in the two 

 preceding ; an excess of alkali, therefore, prevents the separation 

 of curd by rennet. 



17th Exp. To some milk, sufficient tartaric acid was added to 



make it distinctly acid. 



Result : No coagulation took place in the cold. On the appli- 

 cation of heat, the milk coagulated but imperfectly. 



18th Exp. To another portion of milk I added a good deal of 



tartariq acid. 



Result : The milk coagulated after some time, but imper- 

 fectly ; on raising the temperature, more curd fell down. 



In order to precipitate the casein from milk by tartaric acid, 



it is thus necessary to add a very large excess of acid, and at the 



same time to raise the temperature of the milk. 

 These experiments prove thus 



a. That the action of rennet on milk is not the same as that of 

 an acid, inasmuch as rennet coagulates new milk without 

 turning it sour in the least degree. 



b. That rennet can precipitate curd from milk, even when pur- 

 posely made alkaline. 



c. That the whey of inilk, when produced from perfectly sweet or 

 neutral milk, is at first perfectly sweet or neutral, but rapidly 

 turns sour. If made from milk having an alkaline reaction, 

 the whey at first is alkaline ; when from milk slightly acid, 

 the whey likewise is slightly acid. 



d. That rennet ceases to coagulate milk at about 135, and 

 upwards. 



e. That the action of rennet upon milk is more energetic when 

 the milk is slightly acid. This, perhaps, is the reason why 

 some persons recommend putting some sour whey into the 

 milk before or after adding the rennet. 



/. That an excess of alkali prevents the coagulation of milk by 

 rennet. 



