100 ISOMERIC BODIES. 



brought in contact with water without being instantane- 

 ously resolved into new products. These three sub- 

 stances not only yield, on analysis, absolutely the same 

 relative weights of the same elements, but they may be 

 converted and reconverted into one another, even in 

 hermetically closed vessels, that is, without the aid 

 of any foreign matter. (See Appendix, 21.) Again, 

 among those substances which contain no nitrogen, we 

 have aldehyde, a combustible liquid miscible with water, 

 which boils at the temperature of the hand, attracts 

 oxygen from the atmosphere with avidity, and is there- 

 by changed into acetic acid. This compound cannot 

 be preserved, even in close vessels ; for after some 

 hours or days, its consistence, its volatility, and its 

 power of absorbing oxygen, all are changed. It de- 

 posits long, hard, needle-shaped crystals, which at 212 

 are not volatilized, and the supernatant liquid is no long- 

 er aldehyde. It now boils at 140, cannot be mixed 

 with water, and when cooled to a moderate degree crys- 

 tallizes in a form like ice. Nevertheless, analysis has 

 proved, that these three bodies, so different in their 

 characters, are identical in composition. (21) 



3. A similar group of three occurs in the case of 

 albumen, fibrine, and caseine. They differ in external 

 character, but contain exactly the same proportions of 

 organic elements. 



When animal albumen, fibrine, and caseine are dis- 

 solved in a moderately strong solution of caustic pot- 

 ash, and the solution is exposed for some time to a 

 high temperature, these substances are decomposed. 



