Fill a glass tumbler with water, throw upon its surface a few fragments
or thin shavings of camphor, and they will instantly begin to move and
acquire a motion, both progressive and rotatory, which will continue
for a considerable time. During these rotations, if the water be
touched by any substance which is at all greasy, the floating particles
will quickly dart back, and, as if by a stroke of magic, be instantly
deprived of their motion and vivacity.
In like manner, if thin slices of cork be steeped in sulphuric ether
in a closed bottle, for two or three days, and then placed upon the
water, they will rotate for several minutes, like the camphor; until
the slices of cork having discharged all their ether, and become soaked
with water, they will keep at rest.
If the water be made hot, the motion of the camphor will be more rapid
than in cold water, but it will cease in proportionately less time.
Thus, provide two glasses, one containing water at 58 degrees, and the
other at 210 degrees; place raspings of camphor upon each at the same
time; the camphor in the first glass will rotate for about five hours,
until all but a very minute portion has evaporated, while the rotation
of the camphor in the hot water will last only nineteen minutes; about
half the camphor will pass off, and the remaining pieces, instead of
being dull, white, and opaque, will be vitreous and transparent, and
evidently soaked with water. The gyrations, too, which at first will be
very rapid, will gradually decline in velocity, until they become quite
sluggish.
The stilling influence of oil upon waves has become proverbial: the
extraordinary manner in which a small quantity of oil instantly spreads
over a very large surface of troubled water, and the stealthy manner
in which even a rough wind glides over it, must have excited the
admiration of all who have witnessed it.
By the same principle, a drop of oil may be made to stop the motion of
the camphor as follows: throw some camphor, both in slices and in small
particles, upon the surface of water, and while they are rotating, dip
a glass rod into oil of turpentine, and allow a single drop thereof to
trickle down the inner side of the glass to the surface of the water;
the camphor will instantly dart to the opposite point of the liquid
surface, and cease to rotate. If a piece of hard tallow or lard be
employed, the motion of the camphor will be more slowly stopped than
by oil or fluid grease, as the latter spreads over the surface of the
water with greater rapidity.
If a few drops of sulphuric or muriatic acid be let fall into the
water, they will gradually stop the motion of the camphor; but, if
camphor be dropped into nitric acid diluted with its own bulk of water,
it will rotate rapidly for a few seconds and then stop.
If a piece of the rotating camphor be attentively examined with a lens,
the currents of the water can be well distinguished, jetting out,
chiefly from the corners of the camphor, and bearing it round with
irregular force.
The currents, as given out by the camphor, may also be seen by means of
the microscope; a drop or two of pure water being placed upon a slip
of glass, with a particle of camphor floating upon it. By this means,
the currents may be detected, and it will be seen that they cause the
rotations.
Or, a flat watch-glass, called a _lunar_, may be employed, raised a
few inches, and supported on a wire ring, kept steady by thrusting
one end into an upright piece of wood, like a retort stand. Then put
the camphor and water in the watch-glass, and place under the frame a
sheet of white paper, so that it may receive the shadow of the glass,
camphor, &c., to be cast by a steady light placed above, and somewhat
on one side of the watch-glass. On observing the shadow, which may
be considered a magnified representation of the object itself, the
rotations and currents can be distinguished.[B]
[B] Abridged from the Magazine of Popular Science, vol. iii.