Nature works with such simple means! A little more or a little less of
this or that, and behold the difference! A little more or a little less
heat, and the face of the world is changed.
"And the little more, and how much it is,
And the little less, and what worlds away!"
At one temperature water is solid, at another it is fluid, at another it
is a visible vapor, at a still higher it is an invisible vapor that
burns like a flame. All possible shades of color lurk in a colorless ray
of light. A little more or a little less heat makes all the difference
between a nebula and a sun, and between a sun and a planet. At one
degree of heat the elements are dissociated; at a lower degree they are
united. At one point in the scale of temperatures life appears; at
another it disappears. With heat enough the earth would melt like a
snowball in a furnace, with still more it would become a vapor and float
away like a cloud. More or less heat only makes the difference between
the fluidity of water and the solidity of the rocks that it beats
against, or of the banks that hold it.
The physical history of the universe is written in terms of heat and
motion. Astronomy is the story of cooling suns and worlds. At a low
enough temperature all chemical activity ceases. In our own experience
we find that frost will blister like flame. In the one case heat passes
into the tissues so quickly and in such quantity that a blister ensues;
in the other, heat is abstracted so quickly and in such quantity that a
like effect is produced. In one sense, life is a thermal phenomenon; so
are all conditions of fluids and solids thermal phenomena.
Great wonders Nature seems to achieve by varying the arrangement of the
same particles. Arrange or unite the atoms of carbon in one way and you
have charcoal; assemble the same atoms in another order, and you have
the diamond. The difference between the pearl and the oyster-shell that
holds it is one of structure or arrangement of the same particles of
matter. Arrange the atoms of silica in one way and you have a quartz
pebble, in another way and you have a precious stone. The chemical
constituents of alcohol and ether are the same; the difference in their
qualities and properties arises from the way the elements are
compounded--the way they take hold of hands, so to speak, in that
marriage ceremony which constitutes a chemical compound. Compounds
identical in composition and in molecular formulæ may yet differ widely
in physical properties; the elements are probably grouped in different
ways, the atoms of carbon or of hydrogen probably carry different
amounts of potential energy, so that the order in which they stand
related to one another accounts for the different properties of the same
chemical compounds. Different groupings of the same atoms of any of the
elements result in a like difference of physical properties.
The physicists tell us that what we call the qualities of things, and
their structure and composition, are but the expressions of internal
atomic movements. A complex substance simply means a whirl, an intricate
dance, of which chemical composition, histological structure, and gross
configuration are the figures. How the atoms take hold of hands, as it
were, the way they face, the poses they assume, the speed of their
gyrations, the partners they exchange, determine the kinds of phenomena
we are dealing with.
There is a striking analogy between the letters of our alphabet and
their relation to the language of the vast volume of printed books, and
the eighty or more primary elements and their relation to the vast
universe of material things. The analogy may not be in all respects a
strictly true one, but it is an illuminating one. Our twenty-six letters
combined and repeated in different orders give us the many thousand
words our language possesses, and these words combined and repeated in
different orders give us the vast body of printed books in our
libraries. The ultimate parts--the atoms and molecules of all
literature, so to speak--are the letters of the alphabet. How often by
changing a letter in a word, by reversing their order, or by
substituting one letter for another, we get a word of an entirely
different meaning, as in umpire and empire, petrifaction and
putrefaction, malt and salt, tool and fool. And by changing the order of
the words in a sentence we express all the infinite variety of ideas and
meanings that the books of the world hold.
The eighty or more primordial elements are Nature's alphabet with which
she writes her "infinite book of secrecy." Science shows pretty
conclusively that the character of the different substances, their
diverse qualities and properties, depend upon the order in which the
atoms and molecules are combined. Change the order in which the
molecules of the carbon and oxygen are combined in alcohol, and we get
ether--the chemical formula remaining the same. Or take ordinary spirits
of wine and add four more atoms of carbon to the carbon molecules, and
we have the poison, carbolic acid. Pure alcohol is turned into a deadly
poison by taking from it one atom of carbon and two of hydrogen. With
the atoms of carbon, hydrogen, and oxygen, by combining them in
different proportions and in different orders, Nature produces such
diverse bodies as acetic acid, alcohol, sugar, starch, animal fats,
vegetable oils, glycerine, and the like. So with the long list of
hydrocarbons--gaseous, liquid, and solid--called paraffins, that are
obtained from petroleum and that are all composed of hydrogen and
carbon, but with a different number of atoms of each, like a different
number of a's or b's or c's in a word.
What an enormous number of bodies Nature forms out of oxygen by uniting
it chemically with other primary elements! Thus by uniting it with the
element silica she forms half of the solid crust of the globe; by
uniting it with hydrogen in the proportion of two to one she forms all
the water of the globe. With one atom of nitrogen united chemically with
three atoms of hydrogen she forms ammonia. With one atom of carbon
united with four atoms of hydrogen she spells marsh gas; and so on.
Carbon occurs in inorganic nature in two crystalline forms,--the diamond
and black lead, or graphite,--their physical differences evidently being
the result of their different molecular structure. Graphite is a good
conductor of heat and electricity, and the diamond is not. Carbon in the
organic world, where it plays such an important part, is
non-crystalline. Under the influence of life its molecules are
differently put together, as in sugar, starch, wood, charcoal, etc.
There are also two forms of phosphorus, but not two kinds; the same
atoms are probably united differently in each. The yellow waxy variety
has such an affinity for oxygen that it will burn in water, and it is
poisonous. Bring this variety to a high temperature away from the air,
and its molecular structure seems to change, and we have the red
variety, which is tasteless, odorless, and non-poisonous, and is not
affected by contact with the air. Such is the mystery of chemical
change.