504 CONSIDERATION OF CARBON COMPOUNDS. 



acetate, approximately Pb(C 2 H 3 O 2 ) 2 .PbO, a 25 per cent, solution of 

 which is the Liquor plumbi subacetatis, or Goulard's extract, while a 

 solution containing about 1 per cent, is the Liquor plumbi subacetatis 

 dilutus, or lead-water. Other more basic compounds are known. So- 

 called tribasic lead acetate has the formula Pb(C 2 H 3 O 2 ) 2 .2PbO. 



Cupric acetate, Cu(C 2 H 3 O 2 ) 2 H 2 O. The commercial verdigris is a 

 basic acetate of copper, Cu(C 2 H 3 O 2 ) 2 CuO 7 made by the action of 

 dilute acetic acid and atmospheric air on metallic copper. By adding 

 to this basic acetate more acetic acid, the neutral acetate is obtained, 

 but this may be made directly also by dissolving cupric hydroxide 

 or carbonate in acetic acid. It forms deep green, prismatic crystals, 

 which are soluble in water. 



By boiling verdigris with arsenous oxide, cupric aceto-arsenite, 

 3CuAs 2 O 4 -f- Cu(C 2 H 3 O 2 ) 2 , is formed, which is the chief constituent 

 of emerald green or Schweinfurt green, a substance often used as a 

 coloring matter. Paris green is of a similar composition, but less 

 pure. 



Chlorine substitution products of acetic acid. The action of chlor- 

 ine gas and of phosphorus trichloride on acetic acid furnishes an additional 

 proof of the correctness of our views regarding its constitution and, conse- 

 quently, of the constitution of organic acids in general. It has been shown 

 that chlorine in acting on a hydrocarbon (methane) will successively replace all 

 hydrogen present. Similarly we can, by treatment with chlorine, replace that 

 hydrogen in acetic acid which is derived from the hydrocarbon, with the result 

 that monochlor, dichlor, and trichlor acetic acids are formed : 



CH 3 .COOH + 2C1 : : CH 2 C1.COOH + HC1, 

 CH 2 C1.COOH + 2C1 = CHC1 2 .COOH + HC1, 

 CHC1 2 .COOH + 2C1 CC1 3 .COOH -f HC1. 



The fourth atom of hydrogen cannot be directly replaced by chlorine. As it is 

 this carboxyl hydrogen atom to which the acid properties are due the above 

 three compounds have acid properties. 



The action of phosphorus trichloride on water, on methyl alcohol, and on 

 acetic acid takes place thus : 



3**>0 + PC1 3 3HC1 + P(OH) 3 , 



+ PC1 3 = 3CH 3 C1 + P(OH) 3 , 

 3 C 2 H 3 >0 + pcla = 3C 2 H 3 OC1 + P(OH) 3 . 



In all three cases the hydro*xyl group is replaced by chlorine, with the result 

 that hydrogen chloride (hydrochloric acid), methyl chloride, and acetyl chloride 

 are formed. 



