of the Metallic Oxides. 93 



Wiirtz (Compt. Rend, lxxxiii. p. 1141), is formed sponta- 

 neously as a white solid crystalline mass, melting-point 56°, 

 and volatile with difficulty. 



In connection with this question there is no body more 

 interesting than methylene oxide, CH 2 : 0. The corresponding 

 chloride, CH 2 C1 2 , is a liquid, boiling-point 40°. The oxide itself 

 should be naturally a gas, but only assumes this state under 

 the action of heat ; so soon as the heat is withdrawn, it poly- 

 merizes, and is converted into a white solid mass which is 

 insoluble in water, and sublimes at 100°, again changing at 

 higher temperatures into the gaseous CH 2 0, as indicated by 

 its vapour-density. The aldehydes CwH,. CHO are especially 

 characterized by their tendency to polymerization, giving rise 

 to products differing from the original aldehyde in all their 

 physical properties — fusibility, volatility, solubility, &c. Acet- 

 aldehyde may be taken as a type of this class. Under ordinary 

 circumstances it is a liquid, boiling-point 21°. There are two 

 distinct polymers known: — 



(a) Paraldehyde is a liquid, boiling-point 124°, and in the 

 state of gas is represented by (C 2 H 4 0) 3 , as proved by its vapour- 

 density. 



(b) Metaldehyde, (C 2 H 4 0)„, is a solid, crystallizing in 

 beautiful needles, which sublime at 100°, and volatilize without 

 melting at 112-115°, being transformed again into ordinary 

 aldehyde as indicated by its vapour-density. 



Trichloraldehyde, or chloral, CC1 3 . CHO, polymerizes still 

 more easily. When recently distilled, it is a liquid, boiling 

 at 94-95°; after remaining at rest for some time, it is spon- 

 taneously, and sometimes rapidly, converted into what is 

 called insoluble chloral, which is a white, opaque, porcellaneous, 

 hard mass, and, when heated to 180°, re-forms ordinary 

 chloral. 



The aldol, CH 3 . CH(OH) . CH 2 . CHO, of Wiirtz also poly- 

 merizes readily, forming paraldol, which is a beautiful crystal- 

 line solid, melting at 90° (Comptes Eendus, lxxxiii. p. 255). 

 Some aldehydes are only known in the polymeric state, as 

 oxalic aldehyde or glyoxal*, CHO . CHO. 



From analogy, this body ought to be gaseous, or at least 

 a very volatile liquid at the ordinary temperature : — 



* Given the difference in volatility between the chlorides of the nega- 

 tive radicals and the corresponding aldehydes, 



CH 3 . COC1, b.-p. 55°, CH 3 . OOH, b.-p. 21°, 

 we should conclude that ordinary succinic aldehyde was a polymer : — 

 COC1 . CH 3 . CH 2 . COC1, b.-p. 190°, 

 COH . CH 2 . OH 2 . COH, b.-p. 201°-203°. 



