Note 12 bis — Chapter VIII · CARBON AND THE HYDROCARBONS

Maquenne (1892) discovered that carbon is capable of combining with the alkali metals. A 20 p.c. amalgam of the metals was heated to a red heat with charcoal powder in a stream of hydrogen. The compounds so obtained possessed, after the mercury had been driven off, the compositions BaC2, SrC2, CaC2. All these compounds react with water forming acetylene, for example:

BaC₂ + 2H₂O = C₂H₂ + Ba(OH)₂

Maquenne proposes the barium carbide as a source of acetylene. He obtained this compound by heating carbonate of barium, magnesium powder, and retort carbon in a Perreau furnace (BaCO₃ + 3Mg + C = 3MgO + BaC₂). One hundred grams of BaC₂ evolve 5,200 to 5,400 c.c. of acetylene, mixed with about 2–3 p.c. of hydrogen.

The relation of acetylene, C₂H₂, to these metallic carbides is evident from the fact that these metals (Ca, Sr, Ba) replace 2 atoms of hydrogen, and therefore C₂Ba corresponds to C₂H₂, so that they may be regarded as metallic derivatives of acetylene. Moissan (1893) obtained similar carbides directly from the oxides by subjecting them to the action of the voltaic arc, in the presence of carbon, for instance, BaO + 3C = CO + C₂Ba, although at a furnace heat carbon has no action on the oxides CaO, BaO, SrO. Concerning Al₄C₅, see Chapter XVII. Note 38.