168 RESEARCHES UPOISr TEIE CHEMICAL PROPERTIES OF GASES. 



evolved was collected. The copper precipitate consists of CU2C.2, and on treatment 

 with hydrochloric acid undergoes the reaction : 



CU2C2 + 2 HCl = CujClj + C2H2. 



(For an interesting description of this compound, see Keyser, Am. (Jliem. Jr., 1892, 

 p. 285.) 



The precipitate of copper acetylide must be preserved in an unoxidized state 

 previous to its treatment with hydrochloric acid in order to liberate acetylene. If 

 exposed to air during washing, the precipitate is found to remain almost unacted 

 upon by hydrochloric acid, and the yield of acetylene from the copper compound 

 will be insignificant. On this account the washing should be conducted in an atmos- 

 phere of carbon dioxide. 



A very interesting method for the preparation of acetylene by the action of 

 water upon barium carbide has been described by Maquenne ( Compt. Rend., CXY, 

 p. 558). Barium carbonate is reduced by magnesium powder in presence of excess 

 of carbon. As the result of the somewhat violent reaction barium carbide is formed. 

 On moistening with water this carbide is decomposed, yielding nearly pure acetylene. 



Expt. 35. Palladium Asbestos. — . 



Acetylene 3. 1 



Air 96.9 



Oxidation occurred : 



(1) Above melting point of potassium nitrate (339'^). 



(2) " " " " potassium chlorate (359°). 



(3) " " " " potassium nitrate (339°) . 



(4) " " " " " " (3390). 



It was found by careful tests that no CO is formed in the case of the above 

 mixture. In fact, no other products resulted than CO2 and HoO. 



Acetylene seems therefore to be more stable towards heated air in presence of 

 palladium asbestos than the olefines, and in this respect even to rival the paraffins. 



13. Benzol. — The low boiling point of benzol and the common occurrence of 

 its vapor in gas mixtures justify its consideration in connection with the gaseous 

 hydrocarbons. 



JjJxpt. 36. — Air aspirated through benzol (prepared from benzoic acid) and 

 then through palladium asbestos was found to yield carbon dioxide at the following 

 temperatures : 



(1) At 290O (2) At 250" (3) At 270-> 



Benzol vapor causes the palladium to glow very easily ; in fact, much more 

 readily than any of the hydrocarbons heretofore tried. 



