ANIMAL SUBSTANCES. 137 



Acetate of copper or verdigris, and likewise ace- 

 tate of lead, are used for this purpose. Acetic 

 acid is very pungent and caustic. It is very vola- 

 tile, and combines with the metals, earths, and 

 alkalies. 



This acid may also be obtained from wood, by 

 subjecting it to distillation in a retort. In this state 

 it is very impure, being combined with a quantity 

 of empyreumatic oil. This was formerly called py- 

 roligneous acid. When separated from impurities 

 it is essentially the same with vinegar, and is now 

 employed for the same purpose. 



The last change, or final decomposition that 

 vegetables undergo, is called the putrefactive fer- 

 mentation, or putrefaction. Without moisture, heat, 

 and a due access of air, this does not take place. 

 By this vegetables are resolved into their consti- 

 tuent principles, and ammonia is formed. 



ANIMAL SUBSTANCES. 



The elementary principles of animal substances 

 are nearly the same with those of vegetables, but 

 the former contain more nitrogen and phosphorus, 

 and the latter more carbon and hydrogen. 



The proximate constituent parts of animal sub- 

 stances are the following : 



Gelatine, or animal jelly, is very generally dis- 

 persed through all the parts of animals, even in 

 bones, but exists in the greatest quantity in the 

 tendons, membranes, and the skin. It is a viscid 

 substance, very soluble in warm water, but not in 

 alkohol ; insipid, and without smell ; when cold, it 

 congeals into a cohesive, tremulous substance. It 

 forms the basis of soups, broths, &c. and imparts to 



