222 DERIVATIVES OF CARBONIC ACID. 



lively evolution of carbonic anhydride taking place at 

 the same time. Small, colorless prisms, difficultly 

 soluble in water. E"ot fusible without decomposition. 



TENTH GROUP. 



DERIVATIVES OF CARBONIC ACID. 



The isolated bivalent radicle of these compounds 

 carbonyl is carbonic oxide CO. Carbonic acid is only 

 known in the form of the anhydride CO 2 = CO.O ; the 

 true acid CO(OH) 2 cannot be prepared. 



Carbonyl chloride (Phosgene), COC1 2 , is produced 

 by the direct union of chlorine and carbonic oxide in 

 sunlight; or, in the presence of heated spongy platinum, 

 by heating carbon tetrachloride with sulphuric anhy- 

 dride. Can be prepared most readily by heating 20 

 parts chloroform with 50 parts potassium bichromate 

 and 400 parts concentrated sulphuric acid in a flask, 

 connected with an inverted condensing apparatus. 

 Colorless liquid, of a suffocating odor; boiling point, 

 4-8; specific gravity, 1.432 at 0. Is decomposed by 

 water, yielding hydrochloric acid and carbonic anhy- 

 dride ; by alcohols, yielding hydrochloric acid and the 

 ethers of chlorcarbonic (chlorformic) acid COC1.0H, a 

 body which cannot be prepared in a free state. 



Ethyl carbonate, CO(O.C 2 H 5 ) 2 , is formed, together 

 with carbonic oxide, by heating ethyl oxalate with 

 sodium or sodium ethylate at 80 ; by the action of 

 bromine on orthoformic and orthocarbonic ethers (p. 

 35 and 37). Colorless, thin liquid, of a pleasant 

 odor; specific gravity, 0.975 ; boiling point, 126. 



Ethyl carbonic acid, COJ ^ Cannot be 



prepared in a free state. The potassium salt C0 3 .C 2 H 5 .K 

 is formed by saturating a solution of freshly-melted 

 potassa in alcohol with carbonic acid. Laminae, of a 



