In this lesson I will consider carbon and carbon compounds, which are
the bases of all foods and living matter. I will devote but little
attention to theories and technicalities, but will discuss the subject
from scientific and practical standpoints.
Wood, flesh, and other products of vegetable or of animal life blacken
when heated to a sufficiently high temperature. This blackening is
due to the presence of carbon. If such substances are heated with an
abundant supply of air, the carbon combines with oxygen and forms a
colorless gas; that is, the carbon burns.
[Sidenote: Sources of carbon]
The principal form in which carbon occurs in nature is in combination
with other elements. It occurs not only in all living things, but in
their fossil remains, as in coal. All products of plant life contain
carbon, hydrogen, and oxygen. Among the more common of these are
sugar, starch, wood, etc. Most products of animal life contain carbon,
hydrogen, oxygen, and nitrogen. Among these are albumin, fibrin, casein,
etc.
Carbon occurs in the atmosphere in the form of carbon dioxid or carbonic
acid gas. It is also found in the earth in the form of salts of carbonic
acid or carbonates, such as limestone, marble, and chalk.
[Sidenote: Various forms of carbon]
The pure element, carbon, is found in nature in the form of diamonds,
which are pure crystallized carbon. Small diamonds are now made
artificially in electric furnaces. Crystallized carbon also occurs
in nature in the form of graphite, from which lead pencils are made.
Charcoal, lampblack, and coke are forms of amorphous carbon which
contain a very small percentage of impurities.
[Sidenote: Properties of carbon]
Notwithstanding the marked difference in their appearance, the various
forms of carbon have some properties in common. They are insoluble
in all known liquids. They are tasteless, odorless, and infusible at
ordinary temperature. When heated without access of air, they remain
unchanged unless the temperature is very high, in which case they unite
with oxygen and are consumed, forming carbon dioxid.