362 THE WORLD OF LIFE chap. 



The Mystery of Carbon : the Basis of Organised Matter 



and of Life 



It is universally admitted that carbon is the one element 

 which is essential to all terrestrial life. It will be interesting, 

 therefore, to give a brief statement of what is known about 

 this very important substance. Although it is so familiar to 

 us in its solid form as charcoal, or in a more mineralised 

 form as black-lead or graphite, it is doubtful whether it 

 exists uncombined on the earth except as a product of vege- 

 tation. Though graphite (plumbago) is found in some of 

 the earliest rocks, yet it is believed that some forms of 

 vegetation existed much earlier. Graphite has also occurred 

 (rarely) in meteorites, but I am informed by my friend 

 Professor Meldola, that it cannot be decided whether this is 

 derived from carbon-dioxide gas or from gaseous carbon. 

 Sir William Huggins was also doubtful as to the state in 

 which it exists in the sun and comets, whether as carbon- 

 vapour or a hydrocarbon. But the most interesting point 

 for us is that it exists as a constituent of our atmosphere, 

 of which carbon-dioxide forms about 25 1 00 th part, equal to 

 about 7o*oo th part by weight of solid carbon ; and it is from 

 this that the whole of the vegetable kingdom is built up. The 

 leaves of plants contain a green substance named chlorophyll, 

 which by the aid of sunlight can extract the carbon from 

 the gas, and there is no other means known by which this 

 can be done at ordinary temperatures. The chemist has to 

 use the electric spark, or very high temperatures, to perform 

 what is done by the green leaves at the ordinary tem- 

 peratures in which we live. 



The reverse operation of combining carbon with other 

 elements is equally difficult. In Chambers's Encyclopaedia 

 we find the following statement : " At ordinary temperatures 

 all the varieties of carbon are extremely unalterable ; so 

 much so that it is customary to burn the ends of piles of 

 wood which are to be driven into the ground, so that the 

 coating of non-decaying carbon may preserve the inner 

 wood. Wood-charcoal, however, burns very easily, animal 

 charcoal less so ; then follow in order of difficulty of com- 

 bustion coke, anthracite, black-lead, and the diamond." The 



