104 ISOMERIC BODIES. 



the skin, and cannot ])e brought in contact with 

 water without being instantaneously resolved into 

 new products. These three substances 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 thereby 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 deposits long, hard, needle-shaped 

 crystals, Avhich at 212° are not volatilized, and the 

 supernatant liquid is no longer aldehyde. It now 

 boils at 140°, cannot be mixed with water, and when 

 cooled to a moderate degree crystallizes in a form 

 like ice. Nevertheless, analysis has proved, that 

 these three bodies, so different in their characters, 

 are identical in composition. (21) 



8. A similar group of three occurs in the ease of 

 albumen, fibrine, and caseine. They differ in exter- 

 nal character, but contain exactly the same propor- 

 tions of organic elements. 



When animal albumen, fibrine, and caseine are 

 dissolved in a moderately strong solution of caustic 



