ON MILK 197 



quantity of some concrete mineral acid be added, the greatest 

 part of the curds will be again precipitated. They also 

 precipitate on the addition of alkalies and lime-water ; but 

 if too much of these latter be added, the curds will be 

 redissolved. 



(e) If curds dissolved in quicklime or caustic alkali be 

 precipitated by vinegar, a disagreeable hepatic smell is 

 produced. 



The reason why neutral salts, whether saline or terrestrial, 

 gums, and sugar, produce a coagulation of milk (Sec. II. (&)), 

 lies probably in the stronger attraction of water for those 

 salts than for the curds. Infusions of vegetable astringents 

 always show marks of an uncombined acid. It is easily 

 understood why milk is coagulated by them, and many, if 

 not all vegetables, contain some caseous substance. It thence 

 likewise appears why emulsions are coagulated by decoctions 

 of the bark of the cinchona officinalis. 



SECTION V. 



As to the constituent parts of curds, they are probably, 

 like all animal gelatinous substances, still involved in 

 obscurity. This much is certain, that the earth of cheese is 

 the universal animal earth, and consists of phosphoric acid 

 supersaturated with lime. For, after several times abstracting 

 nitrous acid from curds, I at last obtained a white residuum, 

 which was nitrated lime and animal earth. The same earth I 

 obtained from the residuum remaining after the distillation 

 of curds and its further calcination in a crucible by means 

 of nitre : for without nitre this residuum proves very 

 difficult to be reduced to ashes. f Thirty parts of dried curds 

 contained about three parts of animal earth. 



