ACETIC ALDEHYDE. 103 



saturated with dry ammonia. Or a mixture of 4 

 parts sulphuric acid, 12 parts water, and 3 parts alcohol 

 is poured upon 3 parts potassium bichromate, care 

 being taken to cool the vessel in which the reaction 

 takes place; the vapors, freed of water as well as 

 possible, are taken up by ether and saturated with 

 ammonia. The crystalline ammonia compound, when 

 distilled with sulphuric acid, yields pure aldehyde, 

 which can be obtained free of water by rectifying 

 again over calcium chloride. 



Properties. Colorless liquid, of a suffocating odor; . yl 

 specific gravity, 0.807 at 0; boiling point, Zl&r- ^\ 

 mixes with water, alcohol, and ether in every propor- 

 tion. Acts as a powerful reducing agent ; from a silver 

 solution it separates the metal, which forms a beauti- 

 ful specular coating on the sides of the vessel. Com- 

 bines with the bisulphites of the alkalies, forming 

 crystallizing compounds. Phosphorus pentachloride 

 converts it into ethylidene chloride (p. 64). It unites 

 with hydrogen in statu nascendi, forming ethyl alcohol 

 and butylene glycol (which see). All oxidizing agents 

 convert it into acetic acid. Alkalies decompose it, 

 forming resinous bodies. 



Polymeric aldehydes. Small quantities of various 

 substances (chlorcarbonic oxide, hydrochloric acid, sul- 

 phurous acid, zinc chloride, a drop of concentrated 

 sulphuric acid) cause aldehyde to become transformed 

 into polymeric compounds of entirely different pro- 

 perties. At the ordinary temperature paraldehyde 

 Q6jji2Q3 j g produced. This is a colorless liquid, boiling 

 at 124, but slightly soluble in water ; congeals at a 

 low temperature and fuses again at 10.5. At a tem- 

 perature below 0, metaldehyde is principally formed. 

 This is a white, finely crystallizing body, which, with- 

 out previously fusing, sublimes at 112-115, at the 

 same time being partially decomposed into aldehyde. 

 When heated in fused tubes to 112-115, it is com- 

 pletely reconverted into aldehyde. Both of these com- 

 pounds, when distilled with dilute sulphuric acid, 

 hydrochloric acid, etc., are reconverted into aldehyde; 



