Identification of Organic Compounds. 21 



be obtained in a state of chemical purity, and their chemical 

 nature can only be approximately ascertained by the exami- 

 nation of their degradation products. 



Other substances, on the other hand, are gaseous at 

 ordinary atmospheric temperatures. Under high pressures, 

 and with low temperatures, these substances can now all be 



Fig. 5. 



obtained in a liquid state, and by means of special appara- 

 tus fractionally distilled. As, however, it is seldom neces- 

 sary in biochemical investigation to effect a separation and 

 purification of substances which are under ordinary con- 

 dition gases, the methods need not be referred to in greater 

 detail in this place. 



