Both, the discovery of simple molecules as well as Lavoisier’s scientific revolution, were consequences of the systematic studies of chemistry of gases. Thanks
to the accurate measuring it has been possible to investigate in detail the relationship between mass and volume of various gases. Besides the gravimetry that
comprise the measurements of mass ratios (laws of Dalton and Proust), the studies
were extended with the volumetry, the systematic investigation of ratios of volumes
of gases. William Prout (1785–1850) has found that the ratios of masses of equal
volumes of different gases (under the ceteris paribus conditions of constant pressure and temperature) are whole numbers. This observation Prout has compared
with the fact that relative atomic masses of elements are in principle the integer
products of the relative atomic mass of hydrogen. For instance, one volume unit of
chlorine is 36 times heavier that the same volume of hydrogen, or, the equal volume
of oxygen is 16 times heavier than hydrogen. From these mass ratios for equal
volumes Prout in 1820 derives revolutionary hypothesis: there is only one chemical
element, hydrogen, and all the other elements, i.e. their atoms, are composed from
different numbers of hydrogen atoms. Revolutionarity of this idea is far-reaching
because it implies that atoms are composed from smaller particles—the hydrogen
atoms, which Prout has considered as real elemental particles, giving them the name
protyle (the term composed from Greek words pqxsη tkη). Ernest Rutherford
(1871–1937), the physicist who has discovered the structure of atoms in 20th
century, gave to this fundamental component of atom the name proton, in honour to
William Prout.
By his hypothesis Prout has not only announced the concept about the structure
of atom, he has also established the basis of volumetry, the method from which one
of the most important scientific categories has emerged—the amount of substance
(say, the number of particles). If the volume of chlorine is for 36 times heavier than
the same volume of hydrogen, and if atoms of chlorine are merely aggregates of
atoms of hydrogen, then equal volumes of gases under the ceteris paribus conditions must be composed from the equal number of particles! However, history
of science has this law attributed to the famous Italian chemist. In its final form this
law has been defined by Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto (1776–1856) and all of us know it as Avogadro law [5]. This law
is stimulating because it opens the question about the number of particles that
appear in the referent volume—about their amount—the mole. The unit for the
amount of substance, the new parameter in natural science, is called mol—the
number of molecules in standard volume, and its numerical value, i.e. the number of
particles in 1mol, is known as Avogadro’s constant, although it has been determined many decades after Avogadro. The approximate value of Avogadro constant,
2.686 7805(24)Â10
25 molecules per cubic meter at 0 °C, and 1 atmosphere pressure has for the first time determined by Johann Josef Loschmidt (1821–1895),
who has applied the kinetic theory of gases. In literature, this number is known as
Loschmidt number.
The idea about the constant number of particles in given volume (under the
ceteris paribus conditions) has brought Avogadro and his collaborator Cannizzaro
(Stanislao Cannizzaro, 1826–1910) to the final discovery of molecules consisting
11 Models and Reality
111
to the accurate measuring it has been possible to investigate in detail the relationship between mass and volume of various gases. Besides the gravimetry that
comprise the measurements of mass ratios (laws of Dalton and Proust), the studies
were extended with the volumetry, the systematic investigation of ratios of volumes
of gases. William Prout (1785–1850) has found that the ratios of masses of equal
volumes of different gases (under the ceteris paribus conditions of constant pressure and temperature) are whole numbers. This observation Prout has compared
with the fact that relative atomic masses of elements are in principle the integer
products of the relative atomic mass of hydrogen. For instance, one volume unit of
chlorine is 36 times heavier that the same volume of hydrogen, or, the equal volume
of oxygen is 16 times heavier than hydrogen. From these mass ratios for equal
volumes Prout in 1820 derives revolutionary hypothesis: there is only one chemical
element, hydrogen, and all the other elements, i.e. their atoms, are composed from
different numbers of hydrogen atoms. Revolutionarity of this idea is far-reaching
because it implies that atoms are composed from smaller particles—the hydrogen
atoms, which Prout has considered as real elemental particles, giving them the name
protyle (the term composed from Greek words pqxsη tkη). Ernest Rutherford
(1871–1937), the physicist who has discovered the structure of atoms in 20th
century, gave to this fundamental component of atom the name proton, in honour to
William Prout.
By his hypothesis Prout has not only announced the concept about the structure
of atom, he has also established the basis of volumetry, the method from which one
of the most important scientific categories has emerged—the amount of substance
(say, the number of particles). If the volume of chlorine is for 36 times heavier than
the same volume of hydrogen, and if atoms of chlorine are merely aggregates of
atoms of hydrogen, then equal volumes of gases under the ceteris paribus conditions must be composed from the equal number of particles! However, history
of science has this law attributed to the famous Italian chemist. In its final form this
law has been defined by Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto (1776–1856) and all of us know it as Avogadro law [5]. This law
is stimulating because it opens the question about the number of particles that
appear in the referent volume—about their amount—the mole. The unit for the
amount of substance, the new parameter in natural science, is called mol—the
number of molecules in standard volume, and its numerical value, i.e. the number of
particles in 1mol, is known as Avogadro’s constant, although it has been determined many decades after Avogadro. The approximate value of Avogadro constant,
2.686 7805(24)Â10
25 molecules per cubic meter at 0 °C, and 1 atmosphere pressure has for the first time determined by Johann Josef Loschmidt (1821–1895),
who has applied the kinetic theory of gases. In literature, this number is known as
Loschmidt number.
The idea about the constant number of particles in given volume (under the
ceteris paribus conditions) has brought Avogadro and his collaborator Cannizzaro
(Stanislao Cannizzaro, 1826–1910) to the final discovery of molecules consisting
11 Models and Reality
111