338 PRINCIPLES OF CHEMISTRY 



CHAPTER VIII 



CARBON AND THE HYDROCARBONS 



IT is necessary to clearly distinguish between the two closely- allied 

 terms, charcoal and carbon. Charcoal is well known to everybody, 

 although it is no easy matter to obtain it in a chemically pure state. 

 Pure charcoal is a simple, insoluble, infusible, combustible substance 

 produced by heating organic matter, and has the familiar aspect of a 

 black mass, devoid of any crystalline structure, and completely in- 

 soluble. Charcoal is a substance possessing a peculiar combination of 

 physical and chemical properties. This substance, whilst in a state of 

 ignition, combines directly with oxygen ; in organic substances it is 

 found in combination with hydrogen, oxygen, nitrogen, and sulphur. 

 But in all these combinations there is no real charcoal, as in the same 

 sense there is no ice in steam. What is found in such combinations is 

 termed ' carbon ' that is, an element common to charcoal, to those 

 substances which can be formed from it, and also to those substances 

 from which it can be obtained. Carbon may take the form of char- 

 coal, but occurs also as diamond and as graphite. Truly no other 

 element has such a wide terminology. Oxygen is always called 

 * oxygen,' whether it is in a free gaseous state, or in the form of 

 ozone, or oxygen in water, or in nitric acid or in carbonic anhydride. 

 But here there is some confusion. In water it is evident that there is 

 no oxygen in a gaseous form, such as can be obtained in a free state, 

 no oxygen in the form of ozone, but a substance which is capable 

 of producing both oxygen, ozone, and water As an element, oxygen 

 possesses a known chemical individuality, and an influence on the 

 properties of those combinations into which it enters. Hydrogen gas 

 is a substance which reacts with difficulty, but the element hydrogen 

 represents in its combinations an easily displaceable component part. 

 Carbon may be considered as an atom of carbon matter, and charcoal 

 as a collection of such atoms forming a whole substance, or mass of 

 molecules of the substance. The accepted atomic weight of carbofl 

 is 12, because that is the least quantity of carbon wliich enters 



