CARBON AND THE HYDROCARBONS 349 



and at an ordinary temperature does not combine with anything ; it 

 is an inactive substance, like nitrogen. 12 But these properties of 

 charcoal change with a rise of temperature ; thus, unlike nitrogen, 

 charcoal, at a high temperature, combines directly with oxygen. 

 This is well known, as charcoal burns in air. Indeed, not only does 

 oxygen combine with charcoal at' a red heat, but sulphur, hydrogen, 

 silicon, and also iron and some other metals 12bis do so at A very 

 high temperature that is, when the molecules of the charcoal have- 

 reached a state of great instability whilst at ordinary temperatures 

 neither oxygen, sulphur, nor metals act on charcoal in any way, 

 When burning in oxygen, charcoal forms carbonic anhydride, C0 2 ,. 

 whilst in the vapours of sulphur, carbon bisulphide, CS 2 , is formed,. 

 and wrought iron, when acted on by carbon, becomes cast iron. 

 At the great heat obtained by passing the galvanic current through- 

 carbon electrodes, charcoal combines with hydrogen, forming acetylene, 

 G 2 H. 2 . Charcoal does not combine directly with nitrogen, but in the- 

 presence of metals and alkaline oxides, nitrogen is absorbed, forming 

 a metallic cyanide, as, for instance, potassium cyanide, KCN. 

 From these few direct combinations which charcoal is capable of 

 entering into, may be derived those numerous carbonaceous compounds 

 which enter into the composition of plants and animals, and can be thus 

 obtained artificially. Certain substances containing oxygen give up a 



12 The unalterability of charcoal under the action of atmospheric agencies, which 

 produce changes in the majority of stony and metallic substances, is often made use of" 

 in practice. For example, charcoal is frequently strewn in boundary ditches. The 

 surface of wood is often charred to render it durable in those places v, here the soil is- 

 damp and wood itself would soon rot. The chambers (or in some works towers) through 

 which acids pass (for example, sulphuric and hydrochloric) in order to bring them into 

 contact with gases or liquids, are filled with charcoal or coke, because f.t ordinary tem- 

 peratures it resists the action of even the strongest acids. 



tt'bis 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 BaC 2 , SrC 2 , CaC 2 . All these compounds react with 

 water forming acetylene, for example : 



BaC 2 + 2H 2 O = 



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 (BaCO 5 + 3Mg + C = 8MgO + BaC 2 ). One hundred grains of BaC 2 evolve 

 6,200 to 5,400 c.c. of acetylene, mixed with about 2-3 p.c. of hydrogen. 



The relation of acetylene, C 2 H 2 , to these metallic carbides is evident from the fact 

 that these metals (Ca, Sr, Ba) replace 2 atoms of hydrogen, and therefore C 2 Ba corre- 

 sponds to C 2 H 2 , 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 + SC = CO + C 2 Ba, 

 although at a furnace heat carbon has no action, on the oxides CaO, BaO, SrO. Con- 

 cerning A1 4 C 5 , see Chapter XVIL Note 88. 



