described Robert Boyle. Special interest for gasses has expressed John Dalton
during his investigations of meteorological appearances in the atmosphere. Dalton
has found, that the composition of air does not depend on the altitude above the sea
level in spite to the fact that oxygen and nitrogen have different densities. It would
be expected that the denser gas prevails in lower atmospheric layers, and the less
dense gas in higher layers.
To explain the constant composition of air, Dalton has used the old-standing idea
about atoms as a heuristic concept [2]. Dalton has immagined atom as an indivisible
particle of chemical element surrounded by the “mantle of heat”. Undoubtedly, the
heat that Lavoisier has included in elements, is for Dalton the component of the
atom, its mantle. The heat mantle is for Dalton the cause that the forces between
equivalent atoms are repulsive, and between different atoms the forces are attractive. Thus, it is expectable that oxygen and nitrogen would tend to mix rather than
to separate in layers, since their atoms are different, and they attract each other. The
concept about the attractive forces between different, and the repulsive forces
between equivalent atoms is one of the origins of chemical dualism, the idea that
has been prevailing through the longer period of the history of chemistry. These
studies led Dalton also to the formulation of the law about the sum of partial
pressures: the total pressure of the mixture of gasses is the sum of the partial
pressures of all its components.
His atomic theory Dalton put in the relation with the real measuring of
macroscopic appearances [3]. Dalton has extended Proust concept by studying
chemical substances which have the same elements, but combined in different ratios
of their masses. For instance, nitrogen and oxygen form a series of oxides in which
the oxygen/nitrogen mass ratio is different. From these studies Dalton has articulated the known law about the multiple ratios of masses. This law has additionally
supported the theory about atoms, the theory that helped to explain the observation
that in various nitrogen oxides exists the various number of oxygen and nitrogen
atoms. For the first time in the history, the world of atoms, the microcosmos, has
been represented by models.
By reaching out to the methods of Richter and Fischer, who have already
introduced the equivalent mass relationships, Dalton has derived quantitative systematization of chemical elements. Dalton defines the equivalent mass of elements
by using the mass of hydrogen, the element with the smallest weight, as a reference.
If the reference mass of hydrogen is equal to 1, then the relative “atomic mass” of
the element bound to hydrogen can easily be calculated from the known weight
ratio of particular element and hydrogen. Within the accuracy of measuring in that
time, Dalton has calculated equivalent masses (today we call it “relative atomic
mass”) of known elements. For instance, 7 for oxygen, 6 for nitrogen, and 5 for
carbon.
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9 Atoms and Molecules
during his investigations of meteorological appearances in the atmosphere. Dalton
has found, that the composition of air does not depend on the altitude above the sea
level in spite to the fact that oxygen and nitrogen have different densities. It would
be expected that the denser gas prevails in lower atmospheric layers, and the less
dense gas in higher layers.
To explain the constant composition of air, Dalton has used the old-standing idea
about atoms as a heuristic concept [2]. Dalton has immagined atom as an indivisible
particle of chemical element surrounded by the “mantle of heat”. Undoubtedly, the
heat that Lavoisier has included in elements, is for Dalton the component of the
atom, its mantle. The heat mantle is for Dalton the cause that the forces between
equivalent atoms are repulsive, and between different atoms the forces are attractive. Thus, it is expectable that oxygen and nitrogen would tend to mix rather than
to separate in layers, since their atoms are different, and they attract each other. The
concept about the attractive forces between different, and the repulsive forces
between equivalent atoms is one of the origins of chemical dualism, the idea that
has been prevailing through the longer period of the history of chemistry. These
studies led Dalton also to the formulation of the law about the sum of partial
pressures: the total pressure of the mixture of gasses is the sum of the partial
pressures of all its components.
His atomic theory Dalton put in the relation with the real measuring of
macroscopic appearances [3]. Dalton has extended Proust concept by studying
chemical substances which have the same elements, but combined in different ratios
of their masses. For instance, nitrogen and oxygen form a series of oxides in which
the oxygen/nitrogen mass ratio is different. From these studies Dalton has articulated the known law about the multiple ratios of masses. This law has additionally
supported the theory about atoms, the theory that helped to explain the observation
that in various nitrogen oxides exists the various number of oxygen and nitrogen
atoms. For the first time in the history, the world of atoms, the microcosmos, has
been represented by models.
By reaching out to the methods of Richter and Fischer, who have already
introduced the equivalent mass relationships, Dalton has derived quantitative systematization of chemical elements. Dalton defines the equivalent mass of elements
by using the mass of hydrogen, the element with the smallest weight, as a reference.
If the reference mass of hydrogen is equal to 1, then the relative “atomic mass” of
the element bound to hydrogen can easily be calculated from the known weight
ratio of particular element and hydrogen. Within the accuracy of measuring in that
time, Dalton has calculated equivalent masses (today we call it “relative atomic
mass”) of known elements. For instance, 7 for oxygen, 6 for nitrogen, and 5 for
carbon.
76
9 Atoms and Molecules