Such is the title of the fifth part or portion of _Knowledge for the
People: or, the Plain Why and Because:_ containing Attraction or
Affinity--Crystallization--Heat--Electricity--Light and
Flame--Combustion--Charcoal--Gunpowder and Volcanic Fire. We quote a few
articles from most of the heads:--
Why is the science of chemistry so named?
Because of its origin from the Arabic, in which language it signifies
"the knowledge of the composition of bodies."
The following definitions of chemistry have been given by some of our
best writers:--
"Chemistry is the study of the effects of heat and mixture, with the
view of discovering their general and subordinate laws, and of improving
the useful arts."--Dr. Black.
"Chemistry is that science which examines the constituent parts of
bodies, with reference to their nature, proportions, and method of
combination."--Bergman.
"Chemistry is that science which treats of those events or changes, in
natural bodies, which are not accompanied by sensible motions."--Dr.
Thompson.
"Chemistry is a science by which we become acquainted with the intimate
and reciprocal action of all the bodies in nature upon each
other."--Fourcroy.
The four preceding definitions are quoted by Mr. Parkes, in his
_Chemical Catechism_.
Dr. Johnson (from Arbuthnot) defines "chymistry" as "philosophy by
fire."
Mr. Brande says, "It is the object of chemistry to investigate all
changes in the constitution of matter, whether effected by heat,
mixture, or other means."--_Manual_, 3rd edit. 1830.
Dr. Ure says, "Chemistry may be defined the science which investigates
the composition of material substances, and the permanent changes of
constitution which their mutual actions produce."--_Dictionary_,
edit. 1830.
Sir Humphry Davy, in his posthumous work,[6] says, "There is nothing
more difficult than a good definition of chemistry; for it is scarcely
possible to express, in a few words, the abstracted view of an infinite
variety of facts. Dr. Black has defined chemistry to be that science
which treats of the changes produced in bodies by motions of their
ultimate particles or atoms; but this definition is hypothetical; for
the ultimate particles or atoms are mere creations of the imagination. I
will give you a definition which will have the merit of novelty, and
which is probably general in its application. _Chemistry relates to
those operations by which the intimate nature, of bodies is changed, or
by which they acquire new properties._ This definition will not only
apply to the effects of mixture, but to the phenomena of electricity,
and, in short, to all the changes which do not merely depend upon the
motion or division of masses of matter."
Cuvier, in one of a series of lectures, delivered at Paris, in the
spring of last year, says, "the name chemistry, itself, comes from the
word _chim_, which was the ancient name of Egypt;" and he states
that minerals were known to the Egyptians "not only by their external
characters, but also by what we at the present day call their _chemical
characters_." He also adds, that what was afterwards called the Egyptian
science, the Hermetic art, the art of transmuting metals, was a mere
reverie of the middle ages, utterly unknown to antiquity. "The pretended
books of Hermes are evidently supposititious, and were written by the
Greeks of the lower Empire."
Crystallization.
Why are the crystals collected in camphor bottles in druggists' windows
always most copious upon the surface exposed to the light?
Because the presence of light considerably influences the process of
crystallization. Again, if we place a solution of nitre in a room which
has the light admitted only through a small hole in the window-shutter,
crystals will form most abundantly upon the side of the basin exposed to
the aperture through which the light enters, and often the whole mass of
crystals will turn towards it.--Brande.
Why is sugar-candy crystallized on strings, and verdigris on sticks?
Because crystallization is accelerated by introducing into the solution
a nucleus, or solid body, (like the string or stick) upon which the
process begins.
The ornamental alum baskets, whose manufacture was once so favourite a
pursuit of lady-chemistry, were made upon this principle; the forms of
the baskets being determined by wire framework, to which the crystals
readily adhere.
Why is sugar-candy sometimes in large and regular crystals?
Because the concentrated syrup has been kept for several days and nights
_undisturbed_, in a very high temperature; for, if perfect rest and
a temperature of from 120° to 190° be not afforded, regular crystals of
candy will not be obtained.
The manufacture of barley-sugar is a familiar example of
crystallization. The syrup is evaporated over a slow heat, till it has
acquired the proper consistence, when it is poured on metal to cool, and
when nearly so, cut into lengths with shears, then twisted, and again
left to harden.
Heat.
Why does hay, if stacked when damp, take fire?
Because the moisture elevates the temperature sufficiently to produce
putrefaction, and the ensuing chemical action causes sufficient heat to
continue the process; the quantity of matter being also great, the heat
is proportional.
Why is the air warm in misty or rainy weather?
Because of the liberation of the latent heat from the precipitated
vapour.
Why is heated air thinner or lighter than cold air?
Because it is a property of heat to expand all bodies; or rather we
should say, that we call air hot or cold, according as it naturally is
more or less expanded.
Why is a tremulous motion observable over chimney-pots, and slated roofs
which have been heated by the sun?
Because the warm air rises, and its refracting power being less than
that of the colder air, the currents are rendered visible by the
distortion of objects viewed through them.
Within doors, a similar example occurs above the foot-lights of the
stage of a theatre; the flame of a candle, or the smoke of a lamp.
Why are the gas chandeliers in our theatres placed under a large funnel?
Because the funnel, by passing through the roof into the outer air,
operates as a very powerful ventilator, the heat and smoke passing off
with a large proportion of the air of the house.
The ventilation of rooms and buildings can only be perfectly effected,
by suffering the heated and foul air to pass off through apertures in
the ceiling, while fresh air, of any desired temperature, is admitted
from below.--Brande.
Why do heated sea-sand and soda form glass?
Because, by heating the mixture, the cohesion of the particles of each
substance to those of its own kind is so diminished, that the mutual
attractions of the two substances come into play, melt together, and
unite chemically into the beautiful compound called glass.
Why is sand used in glass?
Because it serves for stone; it being said, that all white transparent
stones which will not burn to lime are fit to make glass.
Electricity.
Why is an arrangement of several Leyden jars called an electrical
battery?
Because by a communication existing between all their interior coatings,
their exterior being also united, they may be charged and discharged as
one jar.
The discharge of the battery is attended by a considerable report, and if
it be passed through small animals, it instantly kills them; if through
fine metallic wires, they are ignited, melted, and burned; and gunpowder,
cotton sprinkled with powdered resin, and a variety of other combustibles,
may be inflamed by the same means.
Why is the fireside an unsafe place in a thunder-storm?
Because the carbonaceous matter, or soot, with which the chimney is
lined, acts as a conductor for the lightning.
Why is the middle of an apartment the safest place during a
thunder-storm?
Because, should a flash of lightning strike a building, or enter at any
of the windows, it will take its direction along the walls, without
injuring the centre of the room.
Combustion.
Why does amàdou, or German tinder, readily inflame from flint and steel,
or from the sudden condensation of air?
Because it consists of a vegetable substance found on old trees, boiled
in water to extract its soluble parts, then dried and beat with a
mallet, to loosen its texture; and lastly, impregnated with a solution
of nitre.---Ure.
Why is a piece of paper lighted, by holding it in the air which rushes
out of a common lamp-glass?
Because of the high temperature of the current of air above the flame,
the condensation of which is by the chimney of the glass.
We do not quote these specimens in the precise order in which they occur
in the work, or to show the consecutive or connected interest of the
several articles. In many cases we select them for their brevity and
point of illustration.
[6] Consolations in Travel; or, the Last Days of a Philosopher. 1830.
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