ACETYLENE
Calcium carbide.—Acetylene is prepared from calcium carbide, which on contact with water gives off acetylene.
Calcium carbide is prepared electro-chemically. A mixture of burnt lime and coke is ground and melted up together at very high temperature in an electric furnace, in doing which there is considerable disengagement of carbonic oxide according to the equation:
- CaO + 3C = CaC₂ + CO.
The furnaces used in the production of calcium carbide are of different construction. Generally the furnace is of the nature of an electric arc, and is arranged either as a crucible furnace for intermittent work or like a blast furnace for continuous work.
Besides these there are resistance furnaces in which the heat is created by the resistance offered to the passage of the current by the molten calcium carbide.
The carbonic oxide given off in the process causes difficulty. In many furnaces it is burnt and so utilised for heating purposes. The calcium carbide produced contains as impurities silicon carbide, ferro-silicon, calcium sulphide, and calcium phosphide.
Acetylene (C₂H₂), formed by the decomposition of calcium carbide by means of water (CaC₂ + 2H₂O = Ca(OH)₂ + C₂H₂), furnishes when pure an illuminating gas of great brilliancy and whiteness. Its production is relatively easy. Used for the purpose are (1) apparatus in which water is made to drop on the carbide, (2) apparatus in which the carbide dips into water and is removed automatically on generation of the gas, (3) apparatus in which the carbide is completely immersed in water, and (4) apparatus in which the carbide in tiny lumps is thrown on to water. These are diagrammatically represented in [figs. 20a to 20d] .
| Fig. 20a. | Fig. 20b. |