80 Biological Chemistry. 



polymerizes to form a solid substance trioxymethylamine, 

 (CH 2 0) 3 , which, on heating, " depolymerizes " to yield for- 

 maldehyde again. This is one of the best methods for 

 obtaining the pure aldehyde. Another polymer of formal- 

 dehyde, namely, paraformaldehyde, (CH 2 O) 2 , is known, and 

 is formed when an aqueous solution of the aldehyde is 

 evaporated. 



Acetaldehyde also readily forms a series of polymers. 

 Paraldehyde, (C 2 H 4 0) 3 , is produced when a drop of con- 

 centrated sulphuric acid is added to acetaldehyde. This is 

 a liquid, but slightly soluble in water, of boiling point 

 124, which has distinct narcotic action, and is often em- 

 ployed for producing complete anaesthesia in physiological 

 experiments. Another, a solid polymer, is produced when 

 acetaldehyde is treated with acids at low temperatures. 



The constitutional formula assigned to aldehyde is 



s.O 



and to form- and acet- aldehydes 



H-C/ and CH 

 \H 



It will be noticed that in this formula the hydrogen 

 is not directly united to the oxygen atom as it is in the 

 alcohols, and is not directly replaceable by metals. Further- 

 more, when acetaldehyde is treated with phosphorus penta- 

 chloride, the oxygen alone is replaced by chlorine, two uni- 

 valent chlorine atoms replacing the bivalent oxygen thus 



+ PC1 = POC1 + CH 



-C< 

 X H 



A dichlorethane is thus produced, which differs from 

 the symmetrical ethylene dichloride, CH 2 C1-CH 2 C1 (see 



