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Notes on Chemistry. General Principles.
General doctrines comprehend whatever belongs to heat, light, attraction, & Electricity;
because the influence of these substances may extend to all bodies whatsoever. All other individual
substances in the world fall under the name of particular bodies. A simple body is that which
has
not been decomposed; a compound body is made up of two or more diferent
bodies, either simple or compound. The number of simple bodies is about 50 at present, tho' some of
them may hereafter be decomposed, & the number thereby lessened. Divis. 1
st Chemical Attraction is the kind of Attraction wh we shall particularly notice
in like Attr.; wh acts on
particles, & at
insensible instances & is of 3 kinds Aggregation, Affinites,
& Cohesion. The Ancients believed that Air, Earth, Fire, & Water were the four
simple elements in Nature, but all of these have been decomposed by Modern Chemists. A musket ball
is an example of a body composed of homogenous or similar particles, I.E. particles of lead. And a
ball of brass is a mass of hetrogenous or diferent particles, I.E. of Copper & Zinc. The
Constituent parts
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of a body are the simple elements of which the body is composed, & into wh a body
may be separated by decomposition, as Copper & Zinc are the Constituent parts of brass. The
integrant parts of a body are such
pieces of it as may be obtained by a mechanical operation, as by cuting a
piece of bread, or by rasping a brass ball. We
decompose a body into its
constituent parts, &
divide it into its
integrant parts. The terms hard, soft, friable, denote only diferent
degrees of Cohesion in a body.
Mercury does not adhere to a glass tube, when immersed in it, because its Cohesion is stronger than
its attraction for the glass. Water adheres to a glass tube when put in it, because its attraction
for the glass is greater than its cohesion: per the reason above Mercury assumes a spherical
surface, which it is extremely dificult to prevent, the reverse takes place with water.
Heat & Liquid are principles used to overcome Cohesion. Heat possessing a high repulsive
power, separates the constituent parts of a body to such a distance that their mutual attraction is
destroyed. (Note
Dr Caldwell
objects to the theory of Repulsion,
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as being unfounded in Nature.) The mutual attraction existing between the particles of a
solid & the particles of a liquid overcome the cohesion of the body; this process forms a
solution, & in this way, a fluid dissolves a solid, i.e. by overcoming its Cohesion. In the
same way a body is dissolved by rain, & by another solid, I.E. by the influence of affinity
overcoming its cohesion. In a
few cases, the affinity between the particles of 2 Solids is so much
greater than the individual cohesion of the said solids, th they unite & form a new
Compound. When Salt has been melted by heat, as soon as the heat is withdrawn, the Salt is restored
to its solid form; if it returns slowly & regularly it will form itself into Chrystials
& this is called Christilisation. But should the heat be suddenly removed, & the
solution very quickly restored to a solid, then the figure will be without any determinate form, or
angle. Thus, should lead after being very hot, be suddenly removed from over the fire, &
placed in a very cold place, it will return to a solid, in the form of an irregular mass, without
having any determinate measures. When the cohesion of a solid has been destroyed by the affinity of
another substance, it will
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return to its solid state as soon as they other substance is removed, & it usually
sinks to the bottom of the vessel in the form of a white powder.
Chemical Affinity is the force by wh diff. particles are united in one
body. When two or more boddies by the influence of Chem. Attr. are so united &
assimilated in their particles as to form a homogeneous mass; the process by wh this is done is
called Combination; thus, when we dissolve a piece of Salt in a glass of water so as the salt to
become invisible, the process is called a
Combination. A mixture is a mere
mechanical union of the particles of two boddies, in wh case the particles
altho intimately blended yet exist apart & may be easily known by the muddy colour, wh
mixtures generally have. Thus if we put a quantity of sand or clay into water, & stir them
together, we have a mixture whi may be separated by a mechanical operation called
Filtration. The process by wh the ingredients of a
Combination are separated is called
Decomposition, & if this Decomposition has been performed with the
view of discovering the constituent parts of the compound, it is
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called
Chemical Analysis, & when this decomposed substance reproduced by
the union of its constituent parts, the operation is denominated
Chemical Synthesis.
. . .