THE CHEMISTRY OF CARBON. 
255 
of nature that those who run may read, that carbon was as essen- 
tial to the vitality of the earliest history of the earth as it is now. 
The great deposits of coal on the earth's surface present evidence 
of the vital action of carbon ; but we also find it mineralized in 
other forms, as in the rocks of our neighbourhood. Our limestones 
contain 12 per cent, of carbon, also of vital origin. We can 
hardly venture to say that any form of carbon accessible to man 
has yet been found that does not bear traces of organic origin. 
At Sulphur Bank, in California, the occurrence of carbon com- 
pounds, together with boron, silicon, and sulphur, are suggestive of 
community if not identity of origin ; and the occurrence of large 
supplies of carbonic acid issuing from fissures in mineral veins 
where the above-mentioned minerals, together with gold, silver, 
and other metals are deposited, are further corroborative of this 
view of the case. 
Carbon exists in the amorphous form black and opaque, but it 
also occurs splendidly crystallized, as in the diamond, and of 
extreme hardness. It is found as bort or black diamond equally 
hard, but amorphous as plumbago and as anthracite. 
Diamonds are remarkable as being the most highly valued sub- 
stances known. They so rarely occur pure and perfectly crystallized 
that they have assumed almost fabulous importance. The Koh-i- 
noor belonging to the English crown, less than an ounce in 
weight, is of the value of more than £190,000. Its history, ex- 
tending back to 56 B.C., is most romantic. The uncrystallized 
diamond has lately obtained considerable value for industrial pur- 
poses, for cutting millstones for grinding corn, for driving tunnels 
for railways, and for the working of mines, its hardness remarkably 
well adapting it for boring holes in rocks for blasting purposes, 
rapidity of operation being greatly promoted thereby. 
Some of the most important of the combinations of carbon with 
oxygen were described, as well as some of those with hydrogen, 
having especial reference to the illustration of the fact that these 
compounds may be regarded in the form of molecular elements, 
which will require consideration in some future lecture for satis- 
factory development. 
Finally some remarks were made on the recently reported dis- 
covery of the method of making diamonds by Mactear of Glasgow, 
but their production so as to interfere with the value of natural 
diamonds was considered as exceedingly improbable. 
