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 2) online

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an inch of cast iron was 448,0001bs. avoirdupois, or 200 tons ; whereas, by the
average of thirteen experiments made by Mr. Rennie, in cubes of the same
size, the amount never exceeded 10,3921bs.=not 5 tons !

The desire of obtaining some approximation, which could only be\ accom-
plished by repeated trials on the substances themselves, induced Mr. Rennie to
undertake the following experiments.

The apparatus used for this purpose was a powerful lever of the second class ;
it consisted of a flat bar of the best English iron, about ten feet long, one of the
extremities being formed into a rule-joint, by which it was attached to a stout
and short standard of wrought iron, that was bolted to a massive bed-plate of
cast iron ; the hole in the centre of the joint, and the pin which formed the
fulcrum, were accurately turned, so as to move slowly and freely. The lever
was accurately divided on its lower edge, which was made straight in a line
with the fulcrum. A point or division was selected, at five inches from the
fulcrum, at which place was let in a piece of hardened steel. The lever was
balanced by a weight, and in this state it was ready for operation. But, in
order to keep it as level as possible, a hole was drilled through a projection on
the bed-plate, large enough to admit a stout bolt easily through it, which again
was prevented from turning in the hole by means of a tongue fitting into a
corresponding groove in the hole, so that, in order to preserve the level, it was
only necessary to move the nut, to elevate or depress the bolt, according to the
size of the specimen. But as an inequality of pressure would still arise, from
the nature of the apparatus, the body to be examined was placed between two
pieces of steel, the pressure being communicated through the medium of two
pieces of thick leather, above and below the steel pieces, by which means a
more equal contact of surfaces was obtained. The scale was hung on a loop of
iron, touching the lever in an edge only. At first a rope was used for the
balance weight, which indicated a friction of four pounds, but a chain
diminished the friction one half. Every movable centre was well oiled.

In Mr. llennie's experiments on the cohesive strength of cast iron, to resist
compression, there were four kinds of iron used; viz, I. Iron taken from the
centre of a large block, whose crystals were similar in appearance and mag-
nitude to those evinced in the fracture of what is usually termed gun-metal.

2. Iron taken from a small casting, close-grained, and of a dull grey colour.

3. Iron cast horizontally, in bars of three-eighths ofaninch square, eight inches
long. 4. Iron cast vertically, same size as last. These castings were reduced
equally on every side, to one quarter of an inch square ; thus, removing the
hard external coat, usually surrounding metal castings. They were all subjected
to a gauge ; the bars were then presumed to be tolerably uniform. The weights
used were of the best kind that could be procured, and, as the experiment
advanced, smaller weights were used.

As we have not space for detailing the particulars of each experiment, W2
here add only the average results of them.



776 TENACITY.

Tbe experiments on cast iron, in cubes of one-eighth of an inch, specific gravity
7.033, gave 1439 Ibs. avoirdupois, as the average force required to crush them.

On specimens of the same iron, one-eighth of an inch square, and one-fourth
of an inch long, the average force required was 21 16 Ibs.

On specimens of the same thickness, but varying in length from one-half of
an inch to one inch, the average result was 1758 Ibs.

On cubes of a quarter of an inch of the same metal, gave 9773 Ibs. as the
average result.

On one-fourth of an inch cubes, made from horizontal castings of specific
gravity, 7.113 gave 10,114 Ibs. as the average.

On one-fourth of an inch cubes, vertical castings, specific gravity 7.074, the
average was 11, 136 Ibs.

A prism, having a logarithmic curve for its limits, resembling a column, (it
^as one-fourth of an inch diameter, by one inch long,) broke with 6954 Ibs.

The trials on prisms, of different lengths, one-fourth and one-half horizontal,
gave 9414 Ibs.

The same, vertical, gave 9982 Ibs.

Horizontal castings, varying from three-eighths to six-eights of an inch * ,
gave an average of 8738 Ibs.

Vertical ditto, gave 8536 Ibs.

Experiments on different Metals.

Ibs.
X i cast copper, crumbled with .... .... 7318

,, fine yellow brass reduced .,4 with 321 3A Ibs. with . . 10304

wrought copper . . . ^ . .. 3427f 6440

cast tin a 552 i 966

cast lead . 483'

The experiments on the different metals gave no satisfactory results. The

ifficulty consists in assigning a value to the different degrees of diminution.

^hen compressed beyond a certain thickness, the resistance becomes enormous.

Experiments on the Suspension of Bars.

The lever was used as in the former case, but the metals were held by nippers.
They were made of wrought iron, and their ends adapted to receive the bars,
which, by being tapered at both extremities, and increasing in diameter from
the actual section, and the jaws of the nippers being confined by a hoop, con-
fined both. The bars, which were six inches long, and one quarter square,
\vere thus fairly and firmly grasped

Ibs.

4 inch cast-iron, horizontal 1166

\ ditto ditto, vertical 1218

I ditto cast-steel, previously tilted . . ... 8391
\ ditto blister steel, reduced per hammer .... 8322

i ditto shear steel . . ditto 7977

? ditto Swedish iron . . ditto 4504

\ ditto English iron . . ditto 3492

* ditto hard gun-metal, mean of two trials .... 2273
I ditto wrought copper, reduced per hammer . . . 2112

| ditto cast copper 1192

> ditto fine yellow brass 1123

\ ditto cast tin 296

ditto cast lead 114

Experiments on the Twist of J inch Bars,

To effect the operation of twisting off a bar, another apparatus was prepared.
It consisted of a \vrought-iron lever, two feet Ion?, having an arched head about



TENACITY. 777

one-sixth of a circle, of four feet diameter, of which the lever represented the
radius ; the centre, round which it moved, had a square hole made to receive
the end of the bar to be twisted. The lever was balanced as before, and a scale
hung on the arched head ; the other end of the bar being fixed in a square hole
in a piece of iron, and that again in a vice. By this apparatus, quarter of an
inch bars, from horizontal castings, were twisted with weights in the scale, ave-
raging 91bs. 15oz. The vertical castings took lOlbs. lOoz. as an average.

On different Metals.

Ibs. oz.

Cast steel 17 9 in the scale.

Shear steel 17 1

Blister steal 16 11

English iron, wrought 10 2

Swedish iron, wrought 98

Hard gun-metal 50

Fine yellow brass . . . 411

Copper, cast 45

Tin 17

Lead 10

On Twists of different Lengths. Horizontal,

Ibs. oz.

i by long 73 weight in scale.

| by f ditto 81

| by 1 inch ditto 88

Vertical

i by i ditto 10 1

1 by f ditto 89

I by 1 inch ditto 85

Horizontal twists of quarter of an inch bars, at six inches from the bearing;
took an average of 9 Ibs. 12 oz. in the scale.

Twists of % inch square Bars, cast horizontally.

qrs. Ibs. oz.

close to the bearing 3912 end of the bar hard.

\ ditto . . 2 18 middle of the bar.

at 10 inches from bearing, lever in

the middle 1 24

On Twists of different Materials,

These experiments were made close to the bearing, and the weights were
accumulated in the scale, until the substances were wrenched asunder.

Ibs. oz.

tast steel 199 weight in scale.

Shear steel 17 1

Blister steel 16 11

English iron, No. 1 10 2

Swedish iron 98

Hard gun-metal 50

Fine yellow brass 4 M

Copper 45

Tin 17

Lend , 10

VOL. tt. 5 F



778



'J ENAC1TY.



Miscellaneous Experiments on the Crush of 1 cubic inch.

Ibs. avoir

Elm 1284

American pine 1606

White deal 1928

English oak, mean of two trials 3860

Ditto, of five inches long, slipped with 2572

Ditto, of four inches long, slipped with 5147

A prism of Portland stone, two inches long 805

Ditto, statuary marble 3216

Craig Leith- 8688

In the following experiments on stones, the pressure was communicated
through a kind of pyramid, the base of which rested on the hide leather, and
that on the stone. The lever pressed upon the apex of the pyramid. The
cubes were of one and a half inch.

Spec. grav. Ibs. av.

Chalk 1127

Brick, of a pale red colour 2.085 1265

Roe-stone, Gloucestershire 1449

Red brick, mean of two trials 2.168 1817

Yellow-faced baked Hammersmith paviours three

times 2254

Burnt ditto, mean of two trials 3243

Stourbridge, or fire brick 3864

Derby grit, a red friable sandstone 2.316 ' 7076

Ditto, from another quarry 2.428 9776

Killaly white freestone, not, stratified 2.423 10264

Portland 2.428 10284

Craig Leith, white freestone 2.452 12346

Yorkshire paving, with the strata 2.085 12856

Ditto, against the strata 2.507 12856

White statuary marble, not veined 2.760 13632

firanley Fall sandstone, near Leeds, with strata . . 2.506 13632

Ditto, against the strata 2.506 13632

Cornish granite 2.662 14302

Dundee sandstone or brescia, two kinds .... 2.530 14918

A two-inch cube of Portland 2.423 14918

Craig Lieth, with the strata 2.452 15560

Devonshire red marble, variegated 16712

Compact limestone 2.584 17354

Peterhead granite, hard, close-grained 18636

Black compact limestone, Limerick 2.598 19924

Purbeck 2.599 20610

Black Brabant marble 2.697 20742

Very hard freestone 2,528 21254

White Italian veined marble 2.726 21783

Aberdeen granite, blue kind 2.625 24556

N.B. The specific gravities were taken with a delicate balance, made by
Creighton, of Glasgow, all, with the exception of two specimens, which were by
accident omitted.

Remarks. In observing the results presented by the preceding table, it will
be seen that little dependence can he placed on the specific gravities of stones,
so far as regards their cohesive powers, although the increase is certainly in
favour of their specific gravities. But there would appear to be some undefined
law in the connexion of bodies, with which the specific gravity has little to do.
Thus, statuary marble has a specific gravity above Aberdeen granite, yet a



TENACITY. 779

eohesive power not much above half the latter. Again, hardness is not altogether
a characteristic of strength, inasmuch as the limestones, which yield readily to
the scratch, have nevertheless a cohesive power approaching to granite itself.

Experiments made on the transverse strain of Cast Bars, the ends loose.

Weight of Distance o'f

the bars bearings

Ibs. oz. ft. in. Ibs. av.

Bar of 1 inch square 126 30 897

Ditto of 1 inch ditto 98 28 1086

Half the above bar 14 2320

Bar of 1 inch square through the dia-
gonal 23 28 851

Half the above bar 14 1587

Bar of 2 inches deep, by \ inch thick 95 28 2185

Half the above bar ....... 14 4508

Bars 3 inches deep, by inch thick . 9 15 28 3588

Half the above bar 14 6854

Bar 4 inches, by \ inch thick ... 9 7 28 3979
Equilateral triangles, with the angles up
and down, viz., with the edge or

angle up 9 11 28 1437

With the angle down 97 28 840

Half the first bar 14 3059

Half the second bar 14 1656

A feather-edged bar was cast, whose
dimensions were 2 inches deep

by 2 wide, edge up 10 28 3105

N.B. All these bars contained the same area, though differently distributed
as to their forms.

Experiments made on the Bar o/4 inches deep by} inch thick, by giving it
different forms, the bearings at 2 feet 8 inches, as before.

Ibs.
Bar formed into a semi-ellipse, weighed 7 Ibs . . . . . . 4000

Ditto parabolic on its lower edge 3860

Ditto of 4 inches deep by i inch thick 3979

Experiments on the transverse strain of Bars, one end made fast, the weight
being suspended at the other, at 2 feet 8 inches from the bear ing.

Ibs.

An inch-square bar bore 280

A bar 2 inches deep by an inch thick 539

An inch bar, the ends made fast 1173

The paradoxical experiment of Emerson was tried, which states, that by
cutting off a portion of an equilateral triangle, (see page 114 of Emerson's
Mechanics,) the bar is stronger than before ; that is, a part stronger than the
whole. The ends were loose at two feet eight inches apart, as before. The
edge from which the part was intercepted was lowermost; the weight was ap-
plied on the base above; it broke with 1129 pounds, whereas in the other case
it bore only 840 pounds.

Ibs.

A wire of one-tenth inch diameter of Lead breaks with . 29$ Emerson.
Do. do. Tin do. . 49i

Do. do. Copper do. . 299$

Do. do. Brass do. 360



780 THEATRE.

Ibs,

A wire of one-tenth inch diameter of Silver breaks with . 370 Emerson.

Do. do. Iron do. . 450

Round bar, 1 inch do. do. . 63320 Rumford.

The relative cohesive strength of the metals are, according to Sickengen, as
follow :

Gold 150,955

Silver 190,771

Platina 262,361

Copper 304,696

Soft Iron . . . . . 362,927

Hard Iron 559,880

But their hardness, according to Cavallo, follows this order, viz., Iron, Pla-
tinum, Copper, Silver, Gold, Tin, Lead.

Banks observes that iron is about four times as strong as oak, and six times
as strong as deal. Wood is from seven to twenty times weaker transversely
than longitudinally. It becomes stronger both ways when dry.

TENON. The end of a bar of metal or piece of wood reduced in its
dimensions, so as to fit a hole in another piece, called a mortise, and thus
joining the two together.

TENSION. Is the state of a thing stretched ; this term is much used by
engineers to express the tenacity of metals and other substances, when pulled in
the direction of their length ; thus a wire of one-tenth of an inch in diameter,
is said to be capable of resisting a tension of 450 pounds.

TENTER, trier, or prover, a machine or frame, used in the cloth manufac-
tory, to stretch out the pieces of cloth, and make them set even and square. It
is usually about 41 feet high, and for length exceeds that of the longest piece of
cloth. It consists of several long square pieces of wood, placed like those
which form the barriers of a menage; so, however, as that the lower cross
pieces of wood may be raised or lowered, as is found requisite, to be fixed at any
height, by means of pins. Along the cross pieces, both the upper and the
lower one, are numerous sharp hooked nails, called tenter-hooks, on which the
selvages of the cloth are hooked.

TESSELLATED PAVEMENTS. Pavements of different coloured stones,
tiles, or brick, laid chequer-wise, or like dice (tesselae.) The term tessellated is,
however, extended to all kinds of mosaic patterns or designs.

TEST. Any solid or fluid body, which, added to a substance, teaches us to
distinguish its chemical nature or composition.

THEATRE. An edifice or great room for the public exhibition of scenic
representations, the performance of the drama, of concerts, the delivery of scien-
tific lectures and demonstrations, &c. Considering that the description of a
theatre for the latter purpose will not be out of place in this work, and be ac-
ceptable to our readers, we shall here annex an account of the lecture theatre
of the London Mechanics' Institution ; which may serve the purpose of a model
whereon similar undertakings may be constructed and arranged, making such
alterations and modifications as will better adapt them to other circumstances.

The front of this institution is a large dwelling-house, situated in Southamp-
ton Buildings, at the corner of Staple's Inn, in Holborn ; the lower rooms of
which are employed for the library, reading'rooms, apparatus rooms, laboratory,
&c., and the upper as the private apartments of the Secretary. The theatre is
an entirely new structure, built at the back of, and in connexion with, the
house. The first stone of the theatre was laid on the 2d December, 1824, by
Dr. Birkbeck, the munificent patron and enlightened president of the insti-
tution, and it was opened for use on the 8th of July, 1825.

The annexed Fig. 1 exhibits a plan of the ground floor of the whole building,
on a scale of 1 inch to 20 feet.

The doors in front of the house in Southampton Row are represented at D.
O, office. H, hall and principal staircase. R R, reading-room for the accomo-



THEATRE.



781



dation of the members, supplied with all the periodical journals and reviews,
and where all the books in the library may be perused. L, the library, contain-
ing upwards of 5000 volumes; including almost every work of reputation on




782 THEATRE/

science and literature, which may either be consulted in the reading-room, or
taken home by the members. A R, ante-room to theatre. E, principal entrance
from the house into theatre, e e, side-entrances into theatre. T, the theatre,
bounded by a wall w w w, of a horse-shoe form. G G G are the seats appro-
priated to the members in general. C are those allotted exclusively to members
of the committee ; and V, those for the accommodation of honorary members,
and visitors. N is the entrance into the theatre from Northumberland Court;
and M is that leading from Middle Row, Holborn. S S, two circular spiral
staircases, which proceed from the basement to the gallery. / t is the lecturers'
table, behind which, at P, is a large frame for the exhibition of plans, diagrams,
charts, drawings, &c. ; and when these are made into transparencies, they are
illuminated by a series of gas jets arranged behind the frame. F is a furnace, em-
ployed in the chemical lectures. This furnace, when not in use, is closed by
two folding-doors, which are elegantly painted to correspond with the folding-
doors of the entrance E. The six black spots arranged in a semi-circle, show
the site of the iron pillars that support the principal gallery, which is also of the
horse-shoe form, as shown by the curved dotted line of that figure, (also ex-
hibited in Fig. 2.)

The foregoing plan, although only descriptive of the ground-floor of the build-
ing, will enable us to explain the appropriation of the rooms and offices of the
basement underneath it.

Underneath the hall H, is a kitchen and store-room ; underneath the reading-
room RR, are the porter's rooms; and underneath the library L, is the labora-
tory of the same area, containing furnaces, and other requisites for chemical
investigations. In this room a class of the members meet weekly for mutual in-
struction in chemistry, minerology, &c. Adjoining to the laboratory is a small
workshop, furnished -with an excellent turning-lathe, work-bench, and various
tools for the construction and repair of appai'atus.

Under the theatre is an extensive class-room, lighted by gass, where practi-
cal geometry, perspective, architectural, mechanical, and ornamental drawing,
are regularly taught.

The annexed figure (2.) exhibits a plan of \\\Q first-floor of the house, together
with a plan of the gallery of the theatre. H S is the ascending staircase from the
hall to the first-floor; H G, the gallery leading therefrom to the several apartments,
all the doors or entrances to which are marked with ad. C R is the committee-
room, furnished with a large table, and other requisites, to accommodate the
meetings of the committee of managers, who conduct the affairs of the institu-
tion. This room is 19 feet by 21 feet, and one of the side-walls is covered with
a glass case, furnished with a splendid collection of minerals. A Ris the appa-
ratus-room, or museum, furnished with glass cases around it, containing an
extensive assortment of mechanical, pneumatical, hydrostatical, optical, and elec-
trical apparatus ; besides a great variety of very large diagrams, for the illus-
tration of those subjects ; and an assortment of mineral and geological specimens.
This room is open for the accommodation of the members every Tuesday
evening, from eight till ten o'clock, to afford them opportunities of inspect-
ing the apparatus, conversing together, and explaining to each other the results
of their experience and observations. This mutual interchange of information
is calculated to be productive of important advantages to the members. A class
for mutual instruction in experimental philosophy, also holds a weekly meeting
in this room. M R is another room, similarly appropriated to the last men-
tioned ; it contains various models, and large pieces of apparatus, inconvenient
for exhibition in the museum, (A R,) and an extensive collection of transpa-
rent illustrations of various sciences. B S, the staircase, leading to the upper
floors of the house. The room over the committee-room is a class-room, in
which writing, drawing, the English and Latin languages, &c., and occasionally
stenography, are taught in the different evenings of the week ; and the room
over the museum is also a class-room, where mathematics and arithmetic are
taught. The other rooms in the upper part of the house are the private apart-
ments of the secretary, who resides on the premises. G G G, show the seats
in the gallery of the theatre, rising up an inclined plane ; the front, or lowest



THEATRE.



783



row, being upoii a level with the first-floor of the house, and the highest, or
hack row, being about 17 feet above the lowest. N S is the top of the circular
stone staircase leading from the entrance in Northumberland Court; and M S,
that appertaining to the entrance from Middle Row, Holborn. P is the pit, or



Fig. 2.




rather ground-floor, of the theatre, the plan of which is given in Fig. 1. L L
are two jointed branches for gas-lights, each containing three burners, which
can be moved in various positions, to suit the objects to be illuminated. The



734 THERMOMETER.

dotted lines ooo, show the plan of a lofty rectangular gallery, even with the top
of the semi-circular gallery G, from which there are two entrances at the extre-
mities, and another in the middle.

THEODOLITE. A mathematical instrument used by land-surveyors, for
taking angles, distances, altitudes, &c. This instrument is variously made, and
provided with subordinate apparatus, according to the price, or the requirements
of the purchaser. We shall describe one of the most generally useful. This
consists of two concentric horizontal circles, the inner of which has, at the ends
of one of its diameters, two perpendicular columns, on which rests the horizontal
axis of a small meridian telescope. The vernier of the inner circle is made
fast to an arbitrary division line of the outer one, and both circles are moved,
together with the telescope, until the object sought for appears in its field. The
outer circle is now fixed, and the inner one is turned round, until the telescope
strikes the second object, whose angular distance from the first is to be mea-
sured. The inner circle is now fastened to the outer, and by means of a mi-
crometer screw, the thread of the telescope is brought exactly upon the object.
The arc which the vernier of the inner circle has described on the outer one
measures the angle which the two objects make at the common centre of the
two circles,

THEOREM. A proposition which terminates in theory, and which con-
siders the properties of things already made or done. Or, theorem is a specu-
lative proposition, deduced from several definitions compared together.

THEORY. A doctrine which terminates in speculations, without any view
to the practice or application of it.

THERMOMETER. An instrument for measuring the temperature of bodies ;
founded upon the principle of augmentation in volume of fluids, in proportion
to their absorption ofc caloric ; and as regards aeriform fluids, the principle is
probably very correct : but solids, and still more liquids, expand unequally, by
equal increments of heat. Thermometers were invented about the beginning
of the seventeenth century ; but a knowledge of their author is involved in some
obscurity. For the first half century, after their introduction, they were made in
a very rude and imperfect manner ; but they were at length considerably im-
proved by the Florentine academicians, and received subsequent ameliorations
from Mr. Boyle, Dr. Halley, and Sir Isaac Newton, as well as from contempo-
raneous philosophers on the continent. The changes which the instrument
underwent in their hands, (described in the Oxford Encyclopedia,) we shall not
here insert, as all that had at that time been proposed, were liable to many
conveniences, and could not be considered as exact standards for pointing out
the various degrees of temperature.

The thermometers which at present are in most general use, are Fahrenheit's,
De 1'Isle's, Reaumur's, and Celsius's. Fahrenheit's are used in Britain, De



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 2) → online text (page 114 of 135)