Lithium carbide, Li₂C₂

The Lithium carbide, Li₂C₂ was first prepared by Moissan by the reduction of lithium carbonate with charcoal in the electric furnace -

Li₂CO₃+4C=Li₂C₂+3CO.

Tucker and Moody were unable to prepare the almost pure carbide described by Moissan, and attributed their failure to the very small temperature-interval between the formation and the decomposition of the substance. The carbide is also formed by the interaction of lithium and any of the allotropic modifications of carbon in vacuum at dull red heat; and by the combination of the metal with carbon monoxide or dioxide, or with ethylene or acetylene, an impure product is obtained.

Lithium carbide is a white or grey crystalline substance, its density at 18° C. being 1.65. At bright red heat it is decomposed, and Tucker and Moody found that at 925° C. and a pressure of fifty pounds to the square inch it absorbs nitrogen freely with formation of cyanamide, dicyanamide, and cyanide. It is a powerful reducer, decomposing water energetically at ordinary temperatures with formation of acetylene -

C₂Li₂+2H₂O = C₂H₂+2LiOH.

It ignites in fluorine and chlorine without the application of heat, and on gentle warming in the vapour of bromine, iodine, or phosphorus. It combines with oxygen, sulphur, and selenium at dull redness.

Guntz gives the heat evolved in its action on water as 37.1 Cal., and calculates the heat of formation of the carbide from its elements to be that given by the equation

2[C](diamond)+2[Li]=[Li₂C₂] + 11.3 Cal.

Moissan has prepared an ammonia addition-product of primary lithium acetylide, LiHC₂, although the free primary compound has not been isolated.