[Sidenote: Science teaches the composition of the directly unknowable molecules.]
Not only does science teach the existence of molecules; it looks within them and reveals their composition. For instance, a molecule of the sugar known as glucose, and used by candy makers, is made up of six particles of the element carbon, twelve of the element hydrogen and six of the element oxygen. The particles of carbon in the glucose molecule are so small that if one were divided it would no longer be carbon; the same with the particles of hydrogen and oxygen: if divided they would change into something else--into what is not yet known to man. These smallest particles are called _atoms_ of the elements charcoal, hydrogen and oxygen. If instead of an atom of carbon, hydrogen and oxygen, we write C, H, O, the composition of a molecule of glucose would be written C_{ 6}H_{ 12}O_{ 6}. These are also indisputable facts of science. If the molecules are far beyond the range of our senses, the atoms are of course much further removed from the known world.
[Sidenote: Science teaches the arrangements of the atoms within the molecules.]
But the chemist does not stop here. He is able to state accurately how the invisible, unsensed atoms are arranged within the unknowable molecule. In nature are found several glucose-like sugars, the molecules of which contain the same numbers of carbon, hydrogen and oxygen atoms. The varying properties of these sugars have been found to result from the different arrangements of the atoms within the molecules. The structure of the molecules of three of the most common sugars are as follows:
---------------------------------------------------------------------- I II III DEXTROSE [A] LAEVULOSE [A] GALACTOSE [A] H2=C-OH H2=C-O H H2=C-OH | | | HO-C-H H O-C-H HO-C H | | | HO-C-H H O-C-H HC-OH | | | H-C-O-H H C-O H HC-OH | | | HO-C-H C=O HO-CH | | | H-C=O H C=O H-C=O ----------------------------------------------------------------------
[Footnote A: Dextrose and laevulose combine to form ordinary cane or beet sugar. Dextrose and galactose combine to form the sugar found in milk.]
Referring to the above diagrams it will be observed that although each arrangement contains the same number of atoms, yet, because of the difference in arrangement, they are far from being identical. In fact, the difference in the properties of the sugars may be referred to the arrangement of the atoms in the molecules. This truth is one of the most splendid achievements of modern science. All the facts, here briefly outlined, are included in the atomic hypothesis, which is the foundation of the modern science of chemistry.