BABLAH. The rind or shell which surrounds the fruit of the _mimosa
cineraria_; it comes from the East Indies, as also from Senegal, under
the name of Neb-neb. It contains gallic acid, tannin, a red colouring
matter, and an azotized substance; but the proportion of tannin is
smaller than in sumach, galls, and _knoppern_ (gall-nuts of the common
oak) in reference to that of gallic acid, which is considerable in the
bablah. It has been used, in dyeing cotton, for producing various shades
of drab; as a substitute for the more expensive astringent die-stuffs.
BAGASSE. The sugar-cane, in its dry, crushed state, as delivered from
the sugar-mill. It is much employed for fuel in the colonial
sugar-houses.
BAKING. (_Cuire_, Fr. _Backen_, Germ.) The exposure of any body to such
a heat as will dry and consolidate its parts without wasting them. Thus
wood, pottery, and porcelain, are baked, as well as bread.
BALANCE. To conduct arts, manufactures, and mines, with judgment and
success, recourse must be had, at almost every step, to a balance.
Experience proves that all material bodies, existing upon the surface of
the earth, are constantly solicited by a force which tends to bring them
to its centre, and that they actually fall towards it when they are free
to move. This force is called gravity. Though the bodies be not free,
the effort of gravity is still sensible, and the resultant of all the
actions which it exercises upon their material points, constitutes what
is popularly called their _weight_. These weights are, therefore, forces
which may be compared together, and by means of machines may be made to
correspond or be counterpoised.
To discover whether two weights be equal, we must oppose them to each
other in a machine where they act in a similar manner, and then see if
they maintain an equilibrium; for example, we fulfil this condition if
we suspend them at the two extremities of a lever, supported at its
centre, and whose arms are equal. Such is the general idea of a balance.
The beam of a good balance ought to be a bar of well-tempered steel, of
such form as to secure perfect inflexibility under any load which may be
fitly applied to its extremities. Its arms should be quite equal in
weight and length upon each side of its point of suspension; and this
point should be placed in a vertical line over the centre of gravity;
and the less distant it is from it, the more delicate will be the
balance. Were it placed exactly in that centre, the beam would not
spontaneously recover the horizontal position when it was once removed
from it. To render its indications more readily commensurable, a slender
rod or needle is fixed to it, at right angles, in the line passing
through its centres of gravity and suspension. The point, or rather
edge, of suspension, is made of perfectly hard steel, and turns upon a
bed of the same. For common uses the arms of a balance can be made
sufficiently equal to give satisfactory results; but, for the more
refined purposes of science, that equality should never be presumed nor
trusted to; and, fortunately, exact weighing is quite independent of
that equality. To weigh a body is to determine how many times the weight
of that body contains another species of known weight, as of grains or
pounds, for example. In order to find it out, let us place the
substance, suppose a piece of gold, in the left hand scale of the
balance; counterpoise it with sand or shot in the other, till the index
needle be truly vertical, or stand in the middle of its scale, proving
the beam to be horizontal. Now remove gently the piece of gold, and
substitute in its place standard multiple weights of any graduation,
English or French, till the needle again resumes the vertical position,
or till its oscillations upon either side of the zero point are equal.
These weights will represent precisely the weight of the gold, since
they are placed in the same circumstances precisely with it, and make
the same equilibrium with the weight laid in the other scale.
This method of weighing is obviously independent of the unequal length
as well as the unequal weight of the arms of the beam. For its
perfection two requisites only are indispensable. The first is that the
points of suspension should be rigorously the same in the two
operations; for the power of a given weight to turn the beam being
unequal, according as we place it at different distances from the centre
of suspension, did that point vary in the two consecutive weighings, we
would require to employ, in the second, a different weight from that of
the piece of gold, in order to form an equilibrium with the sand or shot
originally put in the opposite scale; and as there is nothing to
indicate such inequality in the states of the beam, great errors would
result from it. The best mode of securing against such inequality is to
suspend the cords of the scales from sharp-edged rings, upon knife
edges, at the ends of the beam, both made of steel so hard tempered as
to be incapable of indentation. The second condition is, that the
balance should be very sensible, that is, when in equilibrium and
loaded, it may be disturbed, and its needle may oscillate, by the
smallest weight put into either of the scales. This sensibility depends
solely upon the centre or nail of suspension; and it will be the more
perfect the less friction there is between that _knife-edge_ surface and
the plane which supports it. Both should therefore be as hard and highly
polished as possible; and should not be suffered to press against each
other, except at the time of weighing. Every delicate balance of
moderate size, moreover, should be suspended within a glass case, to
protect it from the agitations of the air, and the corroding influence
of the weather. In some balances a ball is placed upon the index or
needle, (whether that index stand above or below the beam,) which may be
made to approach or recede from the beam by a fine-threaded screw, with
the effect of varying the centre of gravity relatively to the point of
suspension, and thereby increasing, at will, either the sensibility, or
the stability of the balance. The greater the length of the arms, the
less distant the centre of gravity is beneath the centre of suspension,
the better polished its central knife-edge of 30°, the lighter the whole
balance, and the less it is loaded; the greater will be its sensibility.
In all cases the arms must be quite inflexible. A balance made by
Ramsden for the Royal Society, is capable of weighing ten pounds, and
turns with one hundredth of a grain, which is the seven-millionth part
of the weight. In pointing out this balance to me one evening, Dr.
Wollaston told me it was so delicate, that Mr. Pond, then astronomer
royal, when making some observations with it, found its indications
affected by his relative position before it, although it was inclosed in
a glass case. When he stood opposite the right arm, that end of the beam
preponderated, in consequence of its becoming expanded by the radiation
of heat from his body; and when he stood opposite the left arm, he made
this preponderate in its turn. It is probable that Mr. Pond had
previously adjusted the centres of gravity and suspension so near to
each other as to give the balance its maximum sensibility, consistent
with stability. Were these centres made to coincide, the beam, when the
weights are equal, would rest in any position, and the addition of the
smallest weight would overset the balance, and place the beam in a
vertical position, from which it would have no tendency to return. The
sensibility in this case would be the greatest possible; but the other
two requisites of level and stability would be entirely lost. The case
would be even worse if the centre of gravity were higher than the centre
of suspension, as the balance when deranged, if free, would make a
revolution of no less than a semi-circle. A balance may be made by a
fraudulent dealer to weigh falsely though its arms be equal, provided
the suspension be as low as the centre of gravity, for he has only to
toss his tea, for instance, forcibly into one scale to cause 15 ounces
of it, or thereby, to counterpoise a pound weight in the other.
Inspectors of weights, &c. are not _au fait_ to this fruitful source of
fraud among hucksters.
BALSAMS. (_Baumes_, Fr. _Balsame_, Germ.) Are native compounds of
ethereal or essential oils, with resin, and frequently benzoic acid.
Most of them have the consistence of honey; but a few are solid, or
become so by keeping. They flow either spontaneously, or by incisions
made from trees and shrubs in tropical climates. They possess peculiar
powerful smells, aromatic hot tastes, but lose their odoriferous
properties by long exposure to the air. They are insoluble in water;
soluble, to a considerable degree, in ether; and completely in alcohol.
When distilled with water, ethereal oil comes over, and resin remains in
the retort.