A certain amount of knowledge of chemistry is eminently useful in almost
every walk of life. An intelligent knowledge of the chemistry involved
in the processes of the kitchen, the dairy, the dye-house, the farm, or
the manufactory, places the possessor engaged in any of these processes
on a different level from the rule-of-thumb worker, who is as ignorant
of the reason for adopting a particular method as he is of the
properties of the materials he employs.
_Technical_ chemistry deals especially with the application of the
principles and processes of chemistry to the arts and manufactures, and
it is to those who are engaged in manufactures of almost every kind that
a knowledge of chemistry is a particular advantage.
It is not a question of expediency alone, but one of absolute necessity
that a technical education, including chemistry as one of its principal
subjects, should form not the least important part of the equipment for
his work of any artisan who is to excel in his employment in
intelligence and skill.
_What is chemistry?_
Chemistry is that branch of science which treats of the _intimate
composition of matter_, and the changes produced in it when subjected to
particular conditions--such as _temperature_, _pressure_, _mass_,
_light_, _catalysis_, etc.
_How does chemistry differ from physics?_
The two branches, physics and chemistry, overlap a great deal, it being
very difficult to draw the line of demarcation between them,
particularly in the higher stages of the _physical_ and _chemical_
changes of matter.
For example, a steel needle rubbed on a magnet in a definite way
undergoes _physical_ change by means of which it acquires the power of
the magnet. On the other hand, a match rubbed on a match-box undergoes a
_chemical_ change by means of which flame is produced. Thus it is
possible to make a distinction between the sciences of physics and
chemistry. A chemical change involves some alteration in the essential
nature of the substance. The match having been ignited has undergone a
permanent change, whereby it is no longer combustible. The physical
change quoted above involves no alteration in the substance itself, and
the acquired property is further only temporary and can be continually
lost and reacquired.
The difficulty occurs in this fact, however, that every chemical change
is accompanied by physical change, and the physical change may often be
the only sign that chemical change has taken place.
_What are the chief divisions of chemistry?_
ORGANIC AND INORGANIC CHEMISTRY.--There are two great divisions in the
science of chemistry, organic and inorganic. The branch which is best
known is that of inorganic chemistry, which covers the chemistry of all
the purely mineral substances. Organic chemistry has to do primarily
with that of substances obtained from animal or vegetable sources. Now,
however, it has resolved itself into the study of the compounds of
carbon, always bearing in mind the fact that many carbon compounds have
no organic origin, and therefore really fall outside the scope of
organic chemistry.
The fundamentals of both branches are the same, and the real reason for
the division is the number of the carbon compounds and their highly
complex character. It is in this realm that the graphic formula is of
most service, and in its organic branch chemistry most nearly approaches
biology.
The branch of inorganic chemistry which treats of the composition, etc.,
of naturally occurring minerals, receives the title of _mineralogical
chemistry_.
PHYSICAL CHEMISTRY explains processes, formulates laws for these
processes, and is divided within itself again into electro-chemistry and
thermo-chemistry, etc. One branch of physical chemistry in which great
strides have been made, is the study of the general properties of gases.
But it is really as much in the realm of physics as it is in the realm
of chemistry.
The study of the chemical nature of substances entering into the
constitution of the animal organism, and the chemical changes taking
place during the life processes of animals, forms the domain of
_physiological chemistry_.
The investigation of the influence of soils, and manures, etc., of
different compositions, upon vegetable life, and the chemical principles
underlying the art of agriculture, are included in the province of
_agricultural chemistry_.
_Pharmaceutical chemistry_ deals with the nature and mode of preparation
of the various drugs, ointments, etc., employed for medicinal purposes.
The science in its relations to the arts, manufactures, and industrial
processes is embraced in the wide titles of _technical_ and _applied
chemistry_.
_What is the difference between theoretical and practical chemistry?_
There are in every science two great divisions. These are known as the
“theory” and the “practice” (or, as they are sometimes called, the
science and the art). The theory of any science is that part of it which
forms the answer in any case to the question “Why?” The practice in the
same way answers to the question “How?”
If we find, for example, that by putting a fire under a vessel of water,
the water gradually begins to boil, as we say, “boils away,” we have
learned something that relates to _practice_. We have learned how to
change water into vapor. It is not necessary that we should know why the
result is brought about, so long as we are satisfied with the result
alone.
But as soon as we begin to wish to bring about any result in the best
possible way, we must inquire why a certain course of action causes the
result; and in the case of the water, we ask why heat should make water
boil and then disappear. The answer to the question “How?” is usually a
simple one. It can be found out by experiment. Once having found out, we
may usually repeat the work as often as we choose.
But the question “Why?” lies deeper, and sometimes cannot be answered at
all. The answer to it is in all cases merely a guess--an attempt to
explain more or less fully and satisfactorily. If we find that our
explanation or theory makes it possible to foretell what will happen in
new cases, then we may safely trust it and believe in it.
_Give a clear, succinct outline of the essentials of theoretical
chemistry._
The whole matter of molecules and atoms is one of _theory_. None of our
senses can enable us to know directly either molecules or atoms. We can
only imagine that they exist, and then give reasons why their existence
makes clear to us the action of elements or of compounds one upon the
other.
But in a course of descriptive chemistry, a good knowledge of
theoretical chemistry is necessary in order to fully understand all that
will be taken up.