338 PRINCIPLES OF CHEMISTRY 



of charcoal is, without doubt, allied to its chemical stability. It is 

 evidently a substance devoid of energy, as charcoal is insoluble in all 

 known liquids, and at an ordinary temperature does not combine n-'iflt 

 anything ; it is an inactive substance, like nitrogen. 12 But these 

 properties of charcoal change with a rise of temperature ; thus, in contra- 

 distinction from 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 icith charcoal at a red lt<'t, 

 but sulphur, hydrogen, and also iron and some other metals do so 

 at a very high temperature that is, when the molecules of the char- 

 coal have reached a state of great instability whilst at ordinary tem- 

 peratures 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, the charcoal combines with hydrogen, forming 

 acetylene, C 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 which are 

 obtained artificially. Certain substances containing oxygen give up a 

 part of it to carbon at a relatively low temperature. For instance, 

 nitric acid when boiled with charcoal gives carbonic anhydride and 

 nitric peroxide. Sulphuric acid is reduced to sulphurous anhydride 

 when heated with carbon. When heated to redness charcoal ab- 

 sorbs oxygen from a large number of the oxides. Even such oxides 

 as those of sodium and potassium, when heated to redness, yield their 

 oxygen to charcoal, although they do not part with it to hydrogen. 

 Only a few of the oxides, like silica (oxide of silicon), and lime (calcium 

 oxide), resist the reducing action of charcoal. Charcoal is capable of 

 changing its physical condition without undergoing any alteration in 

 its essential chemical properties that is, it passes into isomeric or 



12 The unalterability of charcoal under the action of atmospheric influences, 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. Tin- 

 surface of wood is often charred to render it durable in those places where the soil is 

 damp, and wood itself would soon rot. The chambers (or in some works towers i 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, at ordinary tc in 

 peratures, it resists the action of even the most energetic acids. 



