Luke Hebert.

The engineer's and mechanic's encyclopædia, comprehending practical illustrations of the machinery and processes employed in every description of manufacuture of the British Empire .. (Volume 1) online

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gunpowder, when it must be gently dried over a stove, and kept dry for use.
lOOlbs. of curd from the cheese-press will only afford about 30 fbs. of the dry
-curd. To 90 parts of this dried curd, 10 parts of caustic quick lime, made of
blue marble, finely rubbed to powder and searced, and 1 part of camphor, must
be added, and well mixed, by rubbing the whole together with a pallet-knife
upon a stone slab ; and the whole must be then inclosed in bottles, holding
about an ounce each, and well corked immediately afterwards, in order to pre-
vent the access of air to the composition. In this state the cement will remain
good a long time ; and when wanted for use, a little of it must be poured out
upon any flat earthen plate, &c., and, by the aid of a pallet or case-knife, be
instantly mixed with a proper quantity of water, to render it of a fit consistency
for the purpose to which it is to be applied. The bottle must be again carefully
closed, after taking out the quantity of cement required, as, otherwise, the lime
would lose its causticity, upon which its solvent action, or the caseous part of
the cement, entirely depends.

The manufacture of that important and valuable cement, glue, is described
in its initial order in this work.

CENTRAL FORCES. The two antagonist forces by which bodies are
caused to revolve round a central point. As all forces act in right lines, the
tendency of any body moving in a circle is to fly off in a right line forming
a tangent to the circle, and this tendency is called the centrifugal force ; and
the force by which it is restrained from so flying off, and which maintains it in
its curvilinear path, is termed the centripetal force ; and these two forces are
necessarily equal to each other. Dr. Brewster has summed up the whole
doctrine of the central forces in the following propositions. 1. The centrifugal
forces of two unequal bodies moving with the same velocity, and at the same
distance from the centre of motion, are to one another as the respective quantities
of matter in the two bodies. 2. The centrifugal forces of two equal bodies
which perform their revolutions round the central body in the same time, but at
different distances from it, are to one another as their respective distances from
the central body. 3. The centrifugal forces of two bodies which perform their
revolutions in the same time, and whose quantities of matter are inversely as
their distances from the centre, are equal to each other. 4. The centrifugal
force of two equal bodies moving at the same distance from the central body,
but with different velocities, are to one another as the squares of the velocities.
5. The centrifugal forces of two unequal bodies moving at equal distances from
the centre with different velocities, are to one another in the compound ratio of
their quantities of matter and the squares of their velocities. 6. The centrifugal
forces of two equal bodies moving with equal velocities at different distances
from the centre, are inversely as their distances from the centre. 7. The
centrifugal forces of two unequal bodies moving with equal velocities at different
distances from the centre, are to one another as their quantities of matter
multiplied oy their respective distances from the centre. 8. The centrifugal
forces of two unequal bodies moving with unequal velocities at different dis-
tances from the centre, are in the compound ratio of their quantities of matter,
the squares of their velocities, and their distances from the centre.

To find the centrifugal force of any body : Divide the velocity in feet per
second by 4.01, and the square of the quotient by the diameter of the circle ;
the quotient is the centrifugal force when the weight of the body is 1. Hence
the quotient, multiplied by the weight of the body, is the centrifugal force
required. Ex. Required the centrifugal force of the rim of a fly-wheel 20 feet
in diameter, moving with a velocity of 32 feet per second :

32^-r-4.01=8.02 and 8.02 2 -4-20=3.216 times the weight c. f fre rim.



338 CENTRE OF PERCUSSION.

Rule 2. Multiply the square of the number of revolutions per minute, by the
diameter of the circle in feet, and divide the product by the constant number 5870,
and the quotient is the centrifugal force when the weight of the body is 1 ;
and this quotient, multiplied by the weight of the body, is its centrifugal force.
Ex. Required the centrifugal force of a stone weighing 2 Ibs., revolving in a
circle of 4 feet diameter, at the rate of 120 revolutions per minute :

120 3 X 4=57600 and

hence 9.81 X 2=19.62 centrifugal force.

CENTRE OF GRAVITY. A point in any body about which all the
parts are in equilibrio ; so that if the body be suspended or supported by this
point, it will remain in any position in which it may be placed. The centre of
gravity of any plane may be found mechanically as follows : suspend the plane
by a point in or near its perimeter, and when it is at rest, draw across it a
vertical line, passing through the point ; suspend it in like manner by another
point, and draw a vertical line as before ; the intersection of these lines is
the centre of gravity.

CENTRE OF GYRATION is that point in a body revolving about an axis,
into which, if the whole quantity of matter were collected, the same moving force
would generate the same angular velocity. To find the centre of gyration : mul-
tiply the weight of the several parts of the body by the squares of their distances
from the centre of motion, ana divide the sum of the products by the weight
of the whole mass, and the square root of the quotient will be the distance of
the centre of gyration from the centre of motion.

CENTRE OF OSCILLATION is that point in a body suspended from a
point and made to vibrate, in which all its force is collected, and to which point,
if an obstacle were applied, all its motion would cease. To find the centre of
oscillation in a compound pendulum : Multiply all the parts or bodies of which
the pendulum is composed, each by the square of its distance from the point of
suspension, and divide the sum of the products by the product of the whole
weight of the pendulum, multiplied by the distance of the centre of gravity
from the point of suspension.

CENTRE OF PERCUSSION. That point in a body revolving about a fixed
axis into which the whole force or motion is collected ; it is, therefore, that point
of a revolving body which would strike an obstacle with the greatest effect, and
from this property it has received the name of the centre of percussion. The
centres of percussion and of oscillation are generally treated separately, but
the two centres are in the same point, and therefore their properties are the
same. As in bodies at rest the whole weight may be considered as collected in
the centre of gravity, so in bodies in motion, the whole force may be considered
as concentrated in the centre of percussion ; therefore, the weight of the rod
multiplied by the distance of the centre of gravity from the point of suspension,
will be equal to the force of the rod divided by the distance of the centre of
percussion from the same point. For example : suppose a rod, 12 feet long,
and weighing 2 Ibs. per foot, with two balls of 3 Ibs. each, one fixed 6 feet
from the point of suspension, and the other at the end of the rod ; what is
the distance between the points of suspension and of percussion ?

12X2X6=1 44 momentum of rod.
3X6 =18 ditto of first ball.
3X12 =36 ditto of second ball.

198 momentum of balls and rorf;

and the weight of the rod multiplied by the square of its length, and divided
by 3=to the force of the rod ; and the weight of the bal 1 multiplied by the
square of their distance from the point of suspension=to t , force of the ball.
Therefore



CERUSE. 339

24 x 144

=1152 the force of the rod
o

3 X 36= 108 ditto of the first ball
3 X 144= 432 ditto of the second ball

lG92=force of balls and rod,

and 1692-f-198=8.545 feet from the point of suspension. In a slender rod, of
small breadth as compared with its length, the distance of the centre of percussion
is nearly two-thirds of its length from the point of suspension. In an isoceles
triangle, suspended by its apex, and vibrating in a plane perpendicular to itself,
the distance of the centre of percussion is three-fourths of its altitude ; and the
same thing holds with regard to fly-wheels, or wheels in general.

CENTRE, or CENTERING. The framing of timber by which an arch or
vault is supported during its erection. See BRIDGE.

CENTRIFUGAL MACHINE. A machine invented by Mr. Erskine for
raising water by means of a centrifugal force combined with the pressure of the
atmosphere. This machine consists of a vertical tube resting upon a pivot, and
having at top two horizontal hollow arms, near the extremity of each of which,
but on opposite sides, is a valve opening outwards ; whilst near the bottom of
the vertical tube, and below the surface of the water to be raised, is a valve
opening inwards. On the upper part of the arms are two holes, with screw-
caps, and through these holes water is poured previous to setting the machine
in motion ; by which means the air is forced out of the machine, and the water
supported in the tube by the foot-valve at the bottom. The holes in the arms
being secured by their screw-caps, and a rapid rotatory motion being commu-
nicated to the tube, the water in the arms acquires a centrifugal force, opens
the valves near the extremity of the arms, and flies out with a velocity nearly
equal to that of the arms, discharging itself into a circular trough. Although
extremely ingenious and simple, this machine is not equal in effect to a well-
made pump ; and as the fluid is forced up the vertical tube into the arms by
the pressure of the atmosphere, it is incapable of raising water to a height
exceeding 33 feet.

CERATE. A compound of hog's lard or oil with bees' wax, employed in
surgery.

CERIN. That part of common wax which is dissolved by alcohol.

CERIUM. A newly discovered metal found in the mineral cerite. It has
not yet been obtained in a useful metallic form.

CERUSE, or WHITE LEAD, is commonly made by coiling up very thin cast
sheets of lead into rolls, so as to leave a small space between each fold. The
rolls thus formed are lightly jammed into the mouths of a number of earthen-
ware pots, which are about half filled with vinegar. These pots are placed in
a situation where a very gentle heat will cause a slow evaporation of the
vinegar, in order that it may gradually operate upon the lead. A layer of
several hundreds of them are usually deposited either in a bed of tanner's spent
bark, or dung, contained in a wooden frame. Boards are then laid over the
tops of these pots, and on this temporary floor, which is supported by boards
placed edgeways, is laid another layer of pots similarly furnished. Seven such
layers of pots are placed in succession over each other, to form a stack. When
the vinegar is found to be completely evaporated in these stacks, which
generally occupies three months, they are taken down ; the corroded lead is
taken out of the mouths of the pots, but as the adhesion to the latter is very
strong, many of them are broken in getting out the lead, and the poisonous
dust which the workmen inspire by this operation, lamentably impairs their
health, and they are often in consequence afflicted with the disease called the
Devonshire, or painter's colic. To avoid this serious evil, and economize the
process, a different and more mechanical arrangement has been made. The base
of the stack is made of a layer of pots filled with vinegar only ; over these is
supported, by planks on edge, a floor of boards, pierced with numerous holes
to allow the passage of the acid vapour ; on these perforated boards are then



310 CHAIN.

laid the rolls of lead, then another perforated floor, and another layer of rolls,
until the stack is completed. By this arrangement it is said that the manufac-
turer obtains one-third more white lead, saves his pots from breakage, and
avoids the dust so pernicious to the workmen by first sprinkling the rolls with
water. Upon uncoiling the plates, the white substance that falls off is the purest
white lead, and is disposed of for the finest work under the name offtake white ;
a portion of the latter is ground up with water, formed into small lumps, and
sold under the name of ceruse. But all the white lead that is subsequently
taken off the plates is ground up either with water, and sold in large lumps, or
it is ground with oil, and is usually more or less adulterated with whiting, to
suit the various prices at which it is required in the market. As the processes
employed in France and Germany for the manufacture of ceruse appear to be
well worthy of attention, we shall here annex some account of them. In
France the first part of the process consists in dissolving 1741bs. of finely-
ground litharge in 65 Ibs. of pyroligneous acid, of such strength that 22| grains
of this acid will saturate 25 grains of sub-carbonate of soda ; fifteen to twenty
times as much water is usually added. The whole is left for a short time, and
the clear portion being decanted off, some fresh acid and water is poured on the
sediment, to take up any oxide that might have escaped the action of the first
parcel. The decanted solution is run into large shallow covered cisterns, into
which carbonic acid gas is passed through numerous pipes. When the settling
appears to be completed, the whole is passed into a deep cistern, and left there
for some hours, when the liquid part is to be poured off, in order to be combined
with more litharge, some fresh acid being also added. After the desired tint
has been given to the lead, it is well drained, put into glazed pots of the proper
shape to imitate the Dutch white lead leaves, then dried in stoves, and lastly,
packed in blue paper to heighten the effect of its beautiful colour.

In Germany the first part of the process consists in casting the pure lead of
Corinthia into very thin sheets, which is effected by pouring the liquid metal
upon inclined sheets of iron. The sheets of lead are trimmed to a proper size,
and suspended over an acid liquor contained in boxes, which are usually about 5
feet long, 1 foot broad, and 10 inches deep ; and they are pitched internally on
the bottom, and rising therefrom about 2 inches at the sides. Sticks are placed
across the boxes, and the sheets of lead are doubled so as to be suspended in the
middle by them, but so as not to touch each other, nor the acid liquor deposited
underneath them. The liquor in some manufactories is made of equal parts of
vinegar (obtained from crab apples) and wine lees, and about two gallons of this
mixture is apportioned to each box. Some manufacturers use 20 pints of vinegar,
8 pints of wine lees, and 1 Ib. of pearl ash. The usual mode is to dispose the
boxes in a large room heated up to 87 Fahrenheit; a greater heat would
evaporate the acid too fast. In about a fortnight the corrosion is finished,
rendering the sheets about a quarter of an inch thick, and partially covered
with crystals of sugar of lead. Those crystals that are easily detached are
carefully washed ; during this operation a white scum appears, which is taken
off, and a little pearl ash being added to it, it is changed into ceruse of a beautiful
whiteness, and is sold for the choicest purposes ; the remainder is mixed in
different proportions with the pure sulphate of barytes, brought from the Tyrol.

CETINE. The name given by Chevreul to spermaceti, which is extensively
adopted. See FAT.

CHAFF-CUTTING MACHINE, as its name denotes, is a machine for
cutting chaff for cattle, which being an object of some consequence on large
farms, and in establishments employing many horses, a variety of machines
have been invented for the purpose of performing the operation with facility
and dispatch. For a highly-improved machine of this description, see the
article STRAW.

CHAIN. A series of links of metal engaged one within the other; also,
in surveying, a measure of length, made of a certain number of links of iron
wire. That which is most commonly used for this purpose, called Gunter's
chain, is composed of 100 links = 4 poles, or 66 feet; and 1 square chahi=
10,000 links=16 poles ; 10 square chains= 100,000 links=160 poles=l acre



CHEESE. 341

CHAIN PUMP. See PUMPS.

CHALDRON. An English measure for coals, containing 12 sacks, or 36
bushels. The bushel measures are always heaped up, and on shipboard, 21
chaldrons are allowed to the score.

CHALK. A species of carbonate of lime.

CHALYBEATE. Mineral water impregnated with iron is so called.

CHARCOAL. The fixed residue of vegetables exposed to a strong heat
whilst protected from the access of the atmospheric air. In countries where
wood abounds, charcoal is prepared by forming it into a conical stack, covered
with clay and turf to the depth of several inches, leaving an aperture at the
top for the escape of the smoke, and several small apertures at bottom for the
admission of air at first lighting of the pile, but which are carefully closed as
soon as the ignition is supposed complete. ' Charcoal is also made on a great
scale by charring wood in iron cylinders, as described under the head of ACETIC
ACID. Charcoal has been prepared lately in France from turf or peat, and is
said to be superior to that prepared from wood. In a goldsmith's furnace it
fused 11 ounces of gold in 8 minutes; whilst wood charcoal required 16 minutes
to produce the same effect. The malleability of the gold, too, was preserved
in the former instance, but not in the latter. From the scarcity of wood in this
country, pitcoal charred is much used instead of charcoal, and is known by the
name of coke.

CHARGE, in gunnery, the quantity of powder and shot which is necessary
to load a piece of ordnance, in order that when fired it may produce the in-
tended effect. For proving guns the weight of the powder is always equal to
that of the ball ; but the charge of powder generally esteemed sufficient for
service is one-half or one-third the weight of the ball, or even less. Dr.
Hutton found, from many experiments, that the length of the charge producing
the greatest velocity, in guns of various lengths of bore, from 15 to 40 cali-
bres, is as follows :



Length pf bore. Length of charge.

20



( calibres.
30 1

" 3

40 ; ' 20



the length of the bore.



CHAYA ROOT. The root of Oldenlandia umbellata, which grows wild on
the coast of Coromandel, and is likewise there cultivated for the use of the
dyers and calico printers. It is used for the same purposes as madder with us,
to which it is said to be far superior, giving the red so much admired in the
Madras cottons.

CHEESE. An article of food obtained by mixing an acid with milk, which
causes it to coagulate and form a curd ; the curd is then subjected to the action of
a powerful press to separate it from the whey, after which it is set upon racks
to dry. The quantity of curd is less when a mineral acid, than when a vege-
table acid is used ; but the substance which answers best for this purpose, and
indeed which is almost the only one employed in England, is rennet, which is
made by macerating in water the last stomach of a calf, salted and dried for
this purpose. Cheese is made in several parts of England, but that made in
Chester is generally esteemed superior to all others. An excellent account of
the mode of making it will be found in Vol. XL of Tillock's Magazine, taken
from the agricultural report of the county. " If the milk," says the reporter,
" be set together very warm, the curd, as before observed, will be firm ; in this
case, the usual mode is to take a common case knife, and make incisions across
it to the full depth of the blade of the knife, at the distance of about 1 inch,
and again crossways in the same manner, the incisions intersecting at right
angles. The whey rising through these incisions is of a fine pale green colour.
The cheese-maker and two assistants proceed then to break the curd ; this is
performed by their repeatedly putting their hands down into the tub, the cheese-



342 CHEMISTRY.

maker with the skimming dish in one hand, breaking every part of it as they
catch it, raising the curd from the bottom, and still breaking it. This
part of the business is continued till the whole is broken uniformly
small; it generally takes up about 40 minutes, and the curd is then left
covered over with a cloth to subside." The cheese is subsequently broken
by hand, mixed with salt, and put into a vat, in which it is pressed with
loaded boards, and then is turned over upon a cloth into another vat, with a
tin hoop or binder over the upper part of the cheese, and within the sides of
the vat, and then pressed for about 8 hours, being twice turned in the vat
during that time. It is then set to dry, being turned twice a day for the first
week, and then cleared and turned once daily for three weeks longer, after
which it is removed to the common cheese-room, where it is laid upon straw
upon a boarded floor until it acquires the proper hardness.

CHEMISTRY is the science which teaches the composition, properties, and
uses, of all material bodies. It is the business of Mineralogy to investigate the
properties and uses of inorganic substances as they naturally occur, but it is
the office of chemistry to reduce, not only them, but all organic bodies, to their
primitive elements, and having discovered the component parts and their pro-
portions, to aim at their reproduction, when such reproduction would be beneficial
to man. Under this head we shall give but a short sketch of this extensive
science, as it will be necessary to explain the nature and mode of operation of
those potent agents, Light, Heat, and Electricity ; and as each substance which
is the object of chemical research will be described under the initial letter of its
name. For the history of this science we must refer our readers to Brandes
Manual, or some other systematic work on the science, as its details would be
far too multifarious to be compatible with the limits of this work. The science
of chemistry will be found to depend chiefly on the operation of the different
degrees of attraction which the various elementary bodies have for each other.
Every mass of matter on the earth, or diffused through the universe, is found to
tend towards every other mass. This tendency is expressed by the term gravi-
tation) and it is found to increase in intensity as the masses are nearer in the
proportion of the squares of the distances between them. If, however, we
examine this power in individual masses, we shall find it act with much greater
intensity, and to vary its force in different bodies; it is then called affinity.
The former species of attraction, or that acting on masses at sensible distances,
forms the particular object of study in mechanical philosophy ; while the action
of the particles on each other at insensible distances is the object of chemical
philosophy. When this affinity acts between particles of the same kind, it is
called cohesion ; but when it operates between particles of a different kind, it is
called chemical attraction, the attraction of composition, or sometimes simply
affinity. One particle of copper is attached to another particle of copper by
cohesion ; also a particle of sulphate of copper to another particle of the same
substance ; but when a particle of copper unites with a particle of sulphuric or
nitric acid, it is an instance of chemical affinity. The attraction of cohesion,
as well as the power of repulsion, which is opposed to it, are both opposed to
chemical attraction. A lump of sugar or salt is much more readily dissolved
if previously broken into pieces or pulverized, than if left in the solid form
which cohesion imparts to it. Chemical attraction has been distinguished into
three degrees or states of energy : the result of the lowest kind is mixture ; of
the second, solution ; and of the third and most energetic, composition. Chemical
mixture takes place when the particles of two bodies are in a like state, and
the power of cohesion, with regard to them, so far suspended, as to admit of
that freedom of motion between themselves upon which fluidity depends ; thus,
two liquids or two aeriform fluids may admit of mixture, but two solids can be
chemically mixed only by diminishing their cohesion by means of heat to such
a degree as to bring one or both to the state of liquids. Between some fluids
there appears to be no attraction, and hence they do not admit of mixture ;
thus, if water and oil, or water and mercury be agitated together, they will



Online LibraryLuke HebertThe engineer's and mechanic's encyclopædia, comprehending practical illustrations of the machinery and processes employed in every description of manufacuture of the British Empire .. (Volume 1) → online text (page 48 of 115)