operation of filling the boiler at starting is unfortunately deceased, and, in producing a purified by passing through the solution is accomplished by placing a funnel" in a new issue, the publishers have enlisted the rendered fit for use in process No. 2, and may be hole usually provided in the mudhole lid," services of M. A. A. Fesquet, who writes a driven over and passed into a solution of iron, or and "should the fuel used form clinkers on valuable supplement containing much in- of tinned iron from which the tin has been prethe firebars, they should be removed at formation gathered in the foundries of cipitated by No 1 process. By this means the the firebars the author leaves his readers to ing and founding, it will be of some utility of ammonia ordinarily obtained by passing the least once a day," whether the clinkers or Philadelphia. As a practical guide to mould- patentee says he obtains valuable products from the scrap or waste metal in addition to the salt. guess-not an easy matter for the non-tech- in this country, where handbooks of the vapour from crude gas liquor into acid, and nical reader. The following sentence is a kind are usually too vague and uncertain in without material increase of cost or labour. curiosity in itself :-"The beam-engine, their statements to encourage the amateur however, consumes a very considerable to proceed with his study. In some respects excess of fuel over the horizontal, probably the work requires bringing up to the preabout one-seventh more "; and the follow-sent time, for here and there we find supering essentials of a really economical" seded processes spoken of as if they were horizontal engine will be new to engineers, practised now. viz., a stroke of twice the diameter of cylinder, and a fly-wheel of large diameter.

per

are

Turning to the question of fuel, we find the
author saying that "the heat evolved from
the combustion of different kinds of coal
differs considerably, the carbon varying
from 75° to 95°;" no doubt he means
cent.," but he does not say so. And then,
under the head of explosions, we are told
that explosions arising from collapse"
supposed to be caused by the combined
action of a vacuum, often caused by the
sudden admission of water on hot plates, and
considerable internal pressure acting on the
internal flues," which may be clear enough
when explained, but which will certainly
puzzle the non-technical reader, while the
engineer will wonder what the author means
by a "vacuum, ," which is apparently a
favourite idea, for on another page we are
told that "the boiler collapses over the
firebox through a partial vacuum being!
formed."

The Boilermaker's Assistant. By J. COURT-
NEY. Revised and edited by D. K. CLARK.
London: Crosby Lockwood and Co.

As the author of this manual is a working
boilermaker, it should prove a useful book
to those engaged in the same line of business,
especially as the matter is the substance of a
number of notes which the author had made in
his private book of rules, and has been revised
and edited by Mr. D. K. Clark. The earlier
chapters are occupied by definitions and the
simple rules of mensuration and practical
geometry, which are likely to be useful
in drawing, templating, and calculating
boiler-work and tank-work. The methods
of getting out templates, and the rules for
doing the work treated of, are put simply
enough, without the formulæ so objection-
able to the average workman; but unless
we have by accident pitched upon the only
errors in the book, it is evident that it
requires careful revising, for on p. 44, we
are informed that "two 32nd parts" are
equal to th part; on p. 94, 14.14' is said to
equal 159-9396.

The Slide-Valve Practically Explained. By
JOSHUA ROSE, M.E. Philadelphia: H.

C. Baird and Co.

PIANO SOUNDBOARDS. YONSIDERING the position soundboards

a

occupy in relation to stringed instruments, it is rather remarkable that so little has been The Indispensable Bicyclists' Handbook, by large number of works that have from time to written concerning them, notwithstanding the HENRY STURMEY (Coventry: Iliffe and Son) time appeared on kindred subjects. It is indeed keeps up its character, and in its third year fact that a student wishing for practical, or is certainly "indispensable" to all who wish even theoretical, information might search the to keep themselves abreast of the improve-best-furnished libraries in vain for a single mente in bicycles. We think all the novel- textbook on the subject. It is easy to underties-certainly all the useful ones-are stand that practical experimenters would not illustrated or sufficiently described, and there be likely to publish the details of any good is a list of all the makers, with diagrams of thing they might happen to stumble upon; but the well-known designs and the prices. as this reason would not apply to scientists, An Account of Bailey's Testers (W. H. there seems to be only one conclusion to arrive Bailey and Co., Salford) is one of those trade at; that conclusion, however, it would hardly catalogues which gives a deal of useful in- be polite to mention. Meantime, foreigners are pushing us very closely, and it is a question formation besides the announcements of the for the trade whether it is wise to maintain any prices of the articles.--Illustrated Cata- longer that conservative seclusion and jealousy logue of Engineering, Surveying, and Drawing of each other for which they have already Instruments (W. Watson and Son) is another become noted. trade-list containing a number of useful diagrams of instruments used by surveyors and draughtsmen.

A

TREATING WASTE TIN-PLATE.
N improved method of treating waste tin-
plate has been recently patented by Mr.
B. Biggs, of 3, Laurence Pountney-hill, E.C.,
and, as the subject is one of importance, we
give a description of his method. Apart from
the ordinary waste cattings of the works, tin
cans are now adding to the waste at the rate of
many tons a year, and a pecuniarily successful
method of utilising the metals is much needed,
for, although there are one or two processes at
work, we believe the profit is very small when
the clippings can be had without cost of collect-
ing. In treating waste or scrap tinned iron the
patentee dissolves it in sulphuric, hydrochloric,
nitric, or other suitable acid, or partly in one
acid and partly in another, but he prefers to use
dilute sulphuric acid, to which is added about
one per cent. of nitric acid, and precipitate the
tin from the solution by means of sulphuretted
hydrogen. This precipitation is termed No. 1
process. The precipitated sulphide of tin is then
dissolved in bydrochloric acid, and the tin thrown
down with zinc; the solution of chloride of tin is
evaporated and crystallised.

tin from the solution of tin and iron, the patentee After removing the precipitate of sulphide of adds to the remaining solution ammonia or carbonate of ammonia, in the form of vapour or otherwise, by distilling ammoniacal liquor (gasliquor), and purifying the vapour by passing it through lime or oxide of iron, and passing the purified vapour or the distillate into the acid solution. By this process (No. 2) the greater part of the iron is precipitated in the form of oxide or carbonate, and the ammonia combining with the acid forms sulphate, or muriate, or the acid used. He then removes the precipitate, nitrate, or other salt of ammonia according to and if it be not in the form of a peroxide, converts it into a peroxide by drying it and exposing it to the action of the atmosphere, and if the peroxide be required in an anhydrous form, heats it in crucibles, or in a suitable furnace. Should the precipitate of oxide of iron contain any basic salts, the patentee sometimes prefers to treat it with an alkali to decompose them before heating the precipitate. The dried hydrated oxide is in a form suitable for use in the purification of coal-gas. In the anhydrous form the oxide is suitable for use in polishing glass or other substances, or as a pigment. After removing the THIS is a new edition of a book which, in remaining solution the vapour from crude amprecipitate obtained by No. 2 process, into the the United States, has had a wide sale

OUR readers are so familiar with Mr. Rose's
method of teaching a subject that we need
do little more than indicate the nature of
the contents of this book, some portions of
which, if we mistake not, have already
appeared in our pages. The author's object
was to present the subject in so simple a
form that those who know nothing about it
may learn all that is necessary by a perusal
of his pages; hence, practical men may
obtain a clear explanation of the slide-valve,
as found in actual practice, by a study of
Mr. Rose's pages, which are freely illustrated,
though the diagrams are no credit to
American engraving or printing.

The Moulder's and Founder's Pocket Guide.
By FRED. OVERMAN, M.E. London:
Sampson Low.

The old theory that the quantity of sound is in direct proportion to the area of the sound. board has now pretty generally given place to the belief that a large area is only advantageous to the lower notes, while the treble portion may be curtailed with benefit. It must be confessed that this theory appears to be strengthened by the surprising power of the treble of a violin as compared with the weakness of its lower notes, and, again, by the greatly improved quality of these same or even lower notes when sounded on an instrument with a larger soundboard, such as the violoncello; but here, it must not be overlooked, the string also is longer; so we must not hastily give too much credit to the soundboard.

In the horizontal grand piano the area of the soundboard has always been carefully adjusted to the pitch of the strings; the length of these

con

was formerly limited only by the consideration
of finding a room, sufficiently large for its acom-
modation; and even at the present time"
cert grands" occasionally attain mammoth
proportions, though as regards what is called
the "drawing-room grands," the tendency has,
for some time past, been to greatly reduce their
length, and that with a result equally satisfac-
tory as regards the tone, as in the example of
the violoncello just referred to, and, curiously
enough, by pursuing an exactly contrary course.
The different area of the soundboard, therefore,
much to do with the result. It must, then,
cannot, in either of these instances, have had
have been due to the greater thickness of the
strings; and a moment's thought will show
how this may be acopunted for. Since, within
certain bounds, it is evident that a thicker
string cannot so readily divide itself into the
nodes requisite to produce the higher bar-
monios, its fundamental must, therefore, more
powerfully synchronise with the pulsations of
that portion of the soundboard, and thus tend
to produce, not only a tone of purer quality,
It is always easy to be wise after the event; and
but to prolong the period of vibration as well.
now that we know that this is the effect prac-
tically attained, we can afford to wonder why
it was not thought of long ago, especially as
the reduction of the old cabinet into the modern
cottage piano had so greatly increased its power
as to be singularly suggestive that a similar
course with regard to horizontal pianos could
not but be equally advantageous.

W. H. Davies. (To be continuedy).

SUGG'S IMPROVEMENTS IN GAS-
BURNERS.

anongst those interested in the arts of taining sulphide of ammonium precipitates the MPROVEMENTS in the arrangement of

moulding and founding. The author is,

moniacal liquor is passed, which vapour con-
gas-burners have been recently patented by
remaining iron as a sulphide of iron, and being Mr. W. Sugg, of Vincent-street, Westminster,

FIG. 3.

construction, without materially interfering with board is in one piece : it is called a cuckoo-feeder.
a successful result; at the same time there are In commencing to make a bellows, begin hy get-
difficulties which a little instruction may assist ting out the middle board A in No. 1: it is
the amateur to surmount. In this and succeeding to be six inches longer than the top-board, so as
papers I intend carefully to describe the separate to leave a ledge three inches wide at each end;
parts of the instrument and the process of manu- on this board draw the size of the top-board, and
facture, and then to show how it is put together,
voiced, and tuned. I know this has been done
before-by myself among others; but fresh
readers are doubtless always gathering round
"ours"; and besides, I find every year's ex-
perience teaches myself something worth im-
parting to others. I shall also describe a wind-
chest, which has neither springs to the valves nor
slides for the various stops, and which may be
made by any ordinary amateur with little more
than a saw, jack plane, and a few boring bits.

The Bellows.

the object of which is to construct a compound
gas-burner for use in railway yards and other
situations where an intense light is required,
and where the use of glass chimneys, which are
needed for argand burners, is objected to. For
this purpose he combines together, say, four or
more batwing or other flat-flame burners in such
manner that the spaces between them will be
equidistant, or nearly so. When constructing a
burner with four batwings he arranges three to
correspond to the angles of an equilateral
triangle, and the fourth is placed in the centre
at a somewhat superior elevation. The flames
of the outer burners thus arranged will barely
reach each other at their adjacent edges. To
insure this result and to remove all tendency of
the flames to curl inwards and interfere with
the perfect combustion of the gas, he arranges
within the triangular figure formed by the
burners a metal guard of corresponding form
having its flat faces presented to the burners,
which guard will guide currents of air up to the
inner side of the flame. Instead of metal this
guard may be made of talc or other suitable
material. The flame of the central burner must
be kept clear of the flames of the exterior
burners, either by diminishing the jet or by
elevating it as above indicated, or by both
means. Transverse guards parallel to the cen-
tral flame may also be employed for directing
the air upwards to the central burner so as to
insure the flatness of the flame. He proposes in
some cases to use two or more burners within
the circumscribing group, taking care so to
arrange them in the way above indicated that
the flames of all the burners shall remain dis-
tinct or be prevented from blending, as other-
wise a forked and irregular mass of flame will
be produced. It will be understood that the
guard which is inserted within the circum-
scribing burners will take the figure correspond-
ing to the arrangement of those burners, In England and France this form of bel-
whatever that may be. A modification of the lows is quite discarded, and the horizontal
arrangement above indicated is, in forming a six-belows is used. The horizontal bellows consists
light burner, to arrange four in a row of cor-
responding size, the two outer ones representing
two angles of a four sided figure, then for the
other angles of this figure to arrange two
burners of larger capacity; the air-guards or
guides in this case will be arranged parallel to
the flames of their respective burners.

In the figure a four-light burner is shown

དའ་

The bellows are to an organ what the lungs are to a human being, as without good lungs a person cannot sing, nor an organ sound, in a satisfactory manner. Various forms of bellows have been used at different times, and at the present time the varieties are numerous, although the idea is the same-viz., one part called the feeder, to collect the wind, and another part to store it until required for use. In Germany; however, the single or diagonal bellows is still made; in this form the bottom-board is a fixture, and the top is lifted by the bellows-blower, which then falls again as the wind is used. There must, however, be at least two of these bellows in an organ, so that one may be supplying wind while the other is being filled by the bellows-blower. In large organs the number is considerably more. In St. George's Church at Doncaster there are twelve; the organ in the church of SS. Peter and Paul at Goerlitz, with 55 stops, has also twelve; the Church of S. Elizabeth at Breslau has eight.

essentially of two parts, one, usually the lower
part, collects the wind, which is then driven into
the upper part, where it is stored until used;
in small organs there is usually only one feeder
to the belows, but in large organs the bellows
have two, four, or six feeders, according to the
plan adopted for working them; in some cases
the feeders are detached from the remainder of
the bellows, and placed in any convenient
position, either inside or outside the case
of the organ. Where vertical feeders are used,
they are generally detached from the reservoir.
The reservoir should always be large enough to
supply the organ easily, so as to maintain a
steady, even tone, and should be so constructed

also the size of the ribs. The floating-frame, trunk-band, and top-board are all exactly the same size; the top-board is sometimes a solid board, but it is much better framed, and panels screwed on, as if anything goes wrong inside the bellows it can be got at easily. The floatingframe B is a frame between the two folds of the reservoir; it should be made of three-quarter stuff, and be 5in. wide, the trunk-band, C, is made of 14in. stuff, and is 3in. deep; it is firmly fixed to the upper side of the middle board, which it materially strengthens; it also allows the wind-trunks to be conveniently fixed to it. After the top-board, floating-frame, and trunk-band are made they should be laid together and when the edges are planed true they should be marked, so that they may finally be put together the same way. The ribs should be made of nice clean balf-inch pine, 34in. wide; the number of ribs for each fold is eight, so that sixteen are required altogether for the reservoir. The ends of the ribs for the inverted or top fold are cut as shown at A, Fig. 4, and the ends of

A

A

FIC.4

as to give the same pressure of wind whether the lower fold, as at B. After the ends are
full or nearly empty. This result is obtained shaped, the edges of the ribs are to be bevelled
by making one of the folds to work inwards (see Fig. 5), which shows a pair of ribs bevelled
and the other outwards. Therefore, as one
fold reduces the internal capacity of the bellows,
the other increases it. In the accompanying
sketches three shapes of bellows are shown. No.

FIC.S

FIC. 8

with three of the jets at the angles of an equilateral triangle, while the fourth is placed A at the centre, and preferably at a superior elevation. The guard, when of metal, will take a triangular form and leave a cross piece for the central burner; but if of glass, for cheapness, it

B

C

FIC.I

will be made circular in form as indicated by 1 is a single-feeder, and is in general use for
the dotted line. The use of compound burners small organs, especially if blown with the foot.
of this kind is believed to give a better result No. 2 is the ordinary double-feeder in general
than by using the same quantity of gas in
separate burners spaced some distance apart;
but it may be questioned whether gas employed
in this manner can compete with the electric
light.

THE ORGAN, AND HOW TO MAKE IT.
By J. DRESSER.*

HE organ has long been a favourite instru

allow a considerable amount of roughness in

• Mr. J. Dromer is our old correspondent "J. D.-W." Having removed his business from Walsall to Birmingham, he is obliged to drop the last initial of his old stars, and thinks he may as well appear under his

FIG. 2.

and laid together; some few leave the edges square, but it does not look so neat as the bevel. The bottom-board is the same size as the topboard when there is only one feeder; it is sometimes made a solid board, but is much better framed, and a panel screwed on. On the bottom-board draw the shape of the ribs. These ribs are more difficult to get a correct shape than is usually imagined, and if they are not correctly made the gussets soon cut through. I had one case, a short time since, where the four gussets of the feeders were cut through, and the organ was so built that it had all to be taken down to get at the bellows; yet it was not by any means an old organ, and was built by a well-known London builder. The ribs for the feeder should be 7in. wide. When finished, the end ribs will be left the full width, but the side ones will be narrower, the amount varying according to the length of the feeder. It will be seen that one piece of stuff 7in. in width makes the two ribs for the sides of the feeder. In the drawing, No. 6, the three boards use for large chamber and church organs. No. are shown as laid down. The diagonal line is then 3 is also a double-feeder, although the bottom | drawn on the side ribs, and the angles for the cor

ners are got by measuring an equal distance from where the diagonal line crosses the line of the end ribs; the feeder ribs are, of course, bevelled in the same way as the others. After getting all the woodwork out, and the trunk-band fixed to the middle board, the valve-holes are to be bored. Some simply bore round holes in groups, while others make a large oblong hole in various parts, and let in a number of small bars of wood across to support the valve; one way is as good as the other, and, like a great many other things in organ-building, it is a matter of fancy. If round holes are used, the number required is two

FIC.6

is made to form a portion of the field-magnets.
But all efforts hitherto made to produce efficient
small dynamo-machines with cores of soft iron only,
have resulted in absolute failure, although men of
the highest genius have made repeated and pro-
longed efforts to solve that most difficult of
problems.

These curious facts conclusively prove that the
theory explanatory of the action of dynamo-
machines, as now universally adopted, viz., the
theory of inductive action and reaction between
the field-magnets and the armature, cannot any
longer be considered complete or satisfactory; for
even wrought iron, especially when occurring in

Experimenters have also for a long time past clung to the idea that the efficiency of an electromotor-or the amount of energy to be obtained from such a machine by means of a current of given strength circulating in the coils of its armature only-bears a definite and direct proportion to the magneto-inductive power of its field-magnets, and that an increase of power in the field-magnets alone must necessarily produce greater capabilities of the machine.

This, however, is a mischievous theory, because erroneous in its very principles, and development would only lead to the hypothesis of perpetual motion. On the contrary, start

of 1 diameter for every square foot of the bellows, the same number being, of course, required in the under and middle boards. When round holes are used, it is better to make them in groups of six each, as shown at Fig. 7; then one valve covers each group. Where oblong holes are used, as Fig. 8, one valve is then used for each hole. In making the frames for the top-board, floating-frame, and under-board, I do not advise mortising and tenoning, but would recommend a mitre-joint, with a cross tongue of hard wood; it is stronger than the mortice and tenon, and it is much easier to make; the ends are mitred like a picture-frame, then a groove an inch deep is made along the mitre with a plough or may be done with a tenon saw and chisel, and the tongue inserted, and well glued in; if well done it is very strong, and will never give (see Fig. 9). The next thing is to cut a hole in the middle of the top-board for a safety-valve; if the top-board is framed and panelled, the hole is cut in the panel and should be about 6in. by 5in., but if the top is a solid board, a hole is made about 10in. by 8in., and a small panel put on, with the valve-hole cut in it; this is then screwed on, and can be removed if anything is wrong with the valve. (To be continued.)

ing from a consideration of the fact that a very small magnetic needle, if acted upon by one of the poles of another and very powerful magnet, has its polarity destroyed or reversed, and that, if one of its poles, say the N pole, is presented to a similar (N) pole of the large magnet, the former will completely lose its characteristic qualities and be attracted by its overpowering opponent, we can only come to the one rational conclusion, that the power of the field-magnets of an electro-motor, as compared to that of the magnet or magnets constituting its armature, should not surpass the limit of some certain ratio, to be

FIC.6

FIG. 10

FIC 7

AN IMPROVED ELECTRO-MOTOR.*
By THEODORE WIESENDANGER.
THILE recently many minds have been at
work with more or less of success to produce
improvements in dynamo-generators of electric
energy, very few have given their special
care and attention to the development of the
electro-motor. Experience has taught us hither-
to that the efficiencies of one and the same
machine for action and reaction, or for use either
as a generator, or by the inverted process as an
electro-motor, stand in a certain and direct pro-
portion to each other, or that our most efficient
generators, such as the Siemens, Brush, and
Gramme, machines prove also the most effective
motors, and on the other hand that inferior
dynamo-machines invariably are inefficient motors.
It would, however, be hazardous to conclude from
these results that this rule should hold good
for all future machines, and from the results
of researches I have recently made, I have
come to the conclusion that the motors which large masses, always contains an appreciable
are to supersede those now in use could not be
employed as generators. Dynamo-machines, such
as now constructed, only prove efficient when their
field-magnets are able to retain at all times (e.g.,
even when the machine stands at rest) a certain
and very considerable amount of residual magnet-
ism, and for that reason their cores are made of
retentive material, hard cast iron, as is the case in
the Brush and Gramme machines: or if the cores
consist of soft iron they are attached to large
masses of hard cast iron, in such a manner that
the latter are inclosed in the magnetic circuit, and
forma part of the cores.

Generators of the same kind, when made small in size, have cores much larger and heavier in proportion, and, moreover, the baseplate, or, as in the Weston machine, a heavy retentive cylinder,

A Paper read before the British Association.

amount of residual magnetism, more especially
after it has once been subjected to strong mag-
netisation, and if the above theory were correct
and complete, then the smallest possible amount of
residual magnetic energy, augmented by repeated
action and reaction, would be sufficient for the start-
ing of such a machine to action. This, however,
experience proves not to be the case. and the
theory, although stoutly adhered to, must be
either abandoned or amended.

The inventors of the most recent electro-motive
engines have worked-perhaps unconsciously
upon the idea that the construction and action of
electro-motors are based altogether upon the
same laws as those of dynamo or magneto
machines, and, in accordance with that assumption,
the field-magnets of the Desprez motor are made
to consist of large and heavy masses of magnetised
steel.

determined yet by experiments carefully conducted, and that, if it surpasses the limit, the capabilities of the machine must be impaired. Acting on this principle, I have constructed a motor in which the power of the field-magnets is as nearly as possible equal to that of an armature, the core of the former being very light and inade entirely of soft iron; and the satisfactory results obtained from this machine are a sure sign that further investigation of the subject and experiments made with a view of determining the exact ratio of power between the magnets and armature will result in further improvement.

Another and very important consideration in the construction of dynamo-machines and electromotors has not yet received that care and attention from scientific investigators which would lead to immediate progress. It is the method of motion of the revolving armature with regard to its approach ing to, or receding from, the poles of the field-magnets. In nearly all the machines now constructed the polar faces of the cores of the field-magnets, and those of the armature, are of such a shape, and the latter is caused to revolve in such a manner, that only in a small portion of the revolution its poles either approach the poles of the field-magnets or recede from them. But the most

successful production of induced currents will be achieved, and the greatest amount of power will be derived from a motor, if attention is paid, not merely to the one condition, that the armature should revolve in the most highly-concentrated magnetic field possible; but also that nearly the entire motion of the revolving armature should be either one of approach or of withdrawal. Let us, first or all, consider the case of a machine with two poles only of field-magnets and two poles of the revolving

armature.

It is usual to give the active faces of the former such a shape that a section of the same represents a portion of a true circle. See Fig. 1. In the ordinary machines now in use the radius of the circle described by the outline of the revolving armature, and that of the larger circle described in portion by the section of the inner or active faces of the poles are nearly the same, and the two circles are concentric. (See Fig 1.) The pole g of the armature only approaches the pole A of the field-magnets while moving from e to d, or where the intensity of the magnetic field of A is at its minimum. When continuing its motion from tor and to f, the pole g can no longer be said to approach A, because the distance between the respective surfaces remains constant.

I therefore propose that the devices shown in Figs. 2 and 3 should be adopted. The radius of the circle, part of which is formed by the section dr, c, is considerably larger than that of the circle described by the outline of the field of motion of the armature; d, r, c is, moreover, considerably less than the half of a circle and the three circles d'r, e, f, e, h, and that described by the outline of the field of motion of the armature are not

concentric. The pole g of the armature, when in motion, approaches the pole A not only in its course from e to C, but also when in the most intense magnetic field of A, viz., whilst moving from C to 'and d. Fig. 4 represents a section of the field-magnets cones, E F and GH,

tains a system of six field-magnets and six poles,
and a compound armature with six poles. The
current is to be reversed six times for each revo-
lution, and to accomplish this I have devised the
following commuta or (see Fig. 10)-In the-e
machines, also, the poles of the field-magnets or
those of the armature may be of such a shape as to
be nearly always approaching to, or receding from,
each other, while in active motion.

on removing the finger, out it goes with a rush, causing an unearthly screak, calculated to delight the infant mind. Hollow playing balls are made of four segments of calendered sheet, put together balloon fashion. Here is one at this stage; it certainly does not look much like a ball, but more like a withered pear, which has resided for some time in a square tube rather too small for it. The next step is to inclose the incipient ball in a hollow The development of most important machines is spherical mould, best made of slate, and to expose destined to reach a certain stage of perfection, it to a vulcanising heat. The air inside the indiawhen further improvements cannot be accom-rubber now expauds, forcing the material into close plished by the inventor unaided; the second and contact with the mould, and when the vulcanisation important factor needed then is the co-operation of is complete, a perfect counterpart of the interior of inventive and investigative talent with capital. the mould is the result. As the included air conThis stage of perfection has been reached in the tracts, the ball, to some extent, collapses, as you steam-engines, gas-engines, printing-machinery, see in the case of these samples; but by cutting a &c., and it may be said to be rapidly approached small circular hole in one of the balls, it, as you see, by the progress made in dynamo-machines and can be made to regain its spherical shape imme electro-motors. diately. In some cases it is considered better to The development of the latter machines is fol- tightly distend the cured balls by compressed air; lowed by the scientific world with greater interest, and this may be effected by attaching a small lump and it evokes more eager expectations than that of of unmixed rubber to the interior of the ball, before other machinery, chiefly because it is not, and can- it is made up, and this lump undergoes no change not be, identified with the solution of a problem in the curing process. When the cured ball is limited within the confines of mechanical difficul- taken from the mould, a sharp-pointed or stingties and commercial interests, but necessitates alike tube is passed through at the point where the further and deeper investigation into that great lump is situated, and air is forced in through this and subtle power, electricity, whose manifestations tube. On withdrawing the tube, the hole closes, are so striking in their effects, so mysterious in and the freshly-divided surface of the unvulcanised their nature, so promising of great results in an rubber unites again. immediate future, so fertile a field of research to the pioneer of science.

THE INDIARUBBER AND GUTTA-
PERCHA INDUSTRIES.-V.*

By THOMAS BOLAS, F.C.S.
(Continued from page 612.)

I do not think I told you anything about the so-called indiarubber sponge, or froth-like rubber, which may be used for toilet purposes, as padding, or as rubbers for cleaning shoes or various other articles. It is made by incorporating with the rubber certain substances which will give off vapour or gas during the process of curing. Among these may be mentioned damp sawdust, crystallised alum, and carbonate of ammonia. The sponge is vulcanised in moulds, which it fills during the act of expaning. An ingenious application of the rubber composition, which, by the bye, may be certain kind of playing-ball. Some of the sponge compounded as follows:

eard poles-pieces N and S, cast in two halves, and HE rings are laid in French chalk and cured by sponge rubber is made in the manufacture of a

mounted on a base-board, to which they are fixed by the two bolts R and T. The same principles may be applied to machines with field-magnets of more than two poles (see Fig. 5); or the armature itself may be made of such a shape as to work under the conditions above stated. Fig. 6. But even if the poles of the armature and those of the field-magnets are of the ordinary shape, a machine with many magnets will be more perfect in its action than one with field-magnets of two poles only. Fig. 7 illustrates a machine in which the armature during nearly the whole of its motion either approaches to, or recedes from, the pole of the field-magnets. In such machines the motion of the poles of the armature is also more in a line, coincident with the line of attraction as exercised between the two systems of poles; while in machines with field-magnets of two poles only the motion of the poles of the armature is at times at angles of 45 degrees to 1 degree from the direct pull.

I may, perhaps, be allowed to call attention to another matter of importance, awaiting further research. We find that in the three types of dynamo-machines, as constructed by Siemens, Gramme, and Wilde, the relative positions of the axes of the field-magnets and those of the armiatures are altogether different. Yet the three systems work well. We are unable, however, to state with certainty, which positions of the axes are the best, or why any one of these positions should be better than the others, and in the face of experience, the theory of tubes or lines of force is little more than a hypothesis, with all its diffusion, vagueness, and uncertainty.

instead of being made of mixed rubber, are manu-
a steam heat; but very often these articles,
factured from cut sheet.

and consists of a stoutish strip of vulcanised rubber
The squeegee is an instrument of American origin,
mounted, scraper fashion, in a piece of wood. The
scraper-like edge of the indiarubber slides with
very great ease over any wet surface, forcing
before it any dirt or foreign matter in a manner
which is surprisingly complete. No doubt you
have all seen the squeegee made use of for cleansing
the roads and pavements in rainy weather. The
squeegee forms an admirable window cleaner, as I
can illustrate to you by applying one to a piece of
dirty glass; but it must always be used in conjunc-
tion with an abundant supply of water, as the
friction between indiarubber and dry glass is very
great. Considerable use is made of the squeegee
in several of the photo-mechanical printing pro-
cesses, which I had the pleasure of illustrating to
you two years ago, as some of you will doubtless

remember.

20 parts washed rubber of low quality.
10 paris red lead or other pigment.
50 parts old vulcanised rubber in a finely divided

100

is wrapped round a small ball of wood, and the whole is then placed in a spherical mould somewhat larger than the wooden core and its rubber envelope. The heat necessary for curing being now applied, the rubber swells and fills the mould. On taking one of these sponge balls into the hand, its softness would naturally cause one to think it was made of a fine quality of rubber, and to wonder at it being sold at the low price charged; but on Door-mats of vulcanised rubber are now being cutting it in two, the mystery is explained: a extensively made use of. The mixture employed wooden core and a coating of very low quality for their manufacture is generally of a very low sponge rubber being its factors. Very many hollow quality; old vulcanised caoutchouc, fibrous mate- articles are made in moulds, in the same manner as rials, and mineral matters, such as whiting, being the hollow balls; not only toys, such as dolls, freely added; about 20 per cent. of a low quality being produced in this way, but also such goods of new rubber, such as African tongue, being often as injection-bottles and analogous articles; the considered sufficient. The material having been calendered to the requisite thickness, a partial and imperfect curing is generally effected at very this stage, the sheets being exposed to a moderate heat between metal plates, these being often corrugated. After this the patterns of the mats are cut out by means of punches and cutters, the device having been stencilled on the sheet by means of French chalk dusted through a perforated metal plate. The mats are next laid in French chalk, and cured by steam. The punchings are worked over again, the slight preliminary curing or setting being insufficient to offer any notable hindrance to this course.

Having so far considered general principles chiefly, I now beg to describe this motor. ABCD is wooden baseboard, EFGH a frame, consisting of the two parallel round rods FE and G H, and the two flat bars F G and EH, made of the best wrought iron, and carefully softened. The four bars are screwed together at the corners, and supported by four brass brackets over the baseboard. A very excellent method of manufacturing mats, These inner rods form the compound core of the but one not adopted to any great extent in this field-magnets, a combination, as it were, of two country, is to mould them in cast-iron moulds, and horseshce magnets, whose similar poles, S. S. and then to cure by the dry heat of the steam-press. N.N. form the junctions. Thus we have, practi- Other methods, such as building up the mats out of cally, two poles only: a S.and a N. pole. Six coils strips, are also occasionally adopted. Nearly related to of insulated copper wire are wound over the doormats are door stops or buffers, articles of condifferent portions of this core, shown in the draw-siderable utility in preventing damage to houses by ing; the active pole-pieces are left exposed for a long distance, bearing no coils. The spindle PL, which carries a Siemens armature of the old form, or an armature with a compound tubular core; the commutator and pulley traverses the flat crossbar FH. The core of the armature is made of sheets

of charcoal-iron, and it bears a coil of stout insu lated copper wire. The commutator is of the orary kind, consisting of two half-tubes of brass, insulated from each other and from the $699, and each forming one of the terminals of Fig. 9 (A, represents a sectional view of a co spoons machine, acting on the same prinmuda, 12, 3, (3) is a view of the two end-castings which bod the held-magnet. This machine con

a continual banging of the doors. Small blocks of
rubber are often set in the door frames of railway
carriages, to receive and deaden the first effects
of the blow resulting from a rapid shutting of the
doors.

In the manufacture of toys, the applications of
caoutchouc are very numerous and often exceed
ingly ingenious. Here is a small air-ball or balloon,
to which is attached a wooden tube, provided with
an indiarubber strip, acting as a reed. The reed
does not vibrate while the balloon is being dis-
tended; and by closing the tube by means of one
finger, the air may be retained in the balloon; but

*Cantor Lectures, delivered before the Society of Arts.

principle of utilising the expansive force of air for being of widespread application in the rubber forcing the rubber up to the sides of the mould industry. Tin or cast-iron moulds are often employed, and, in some cases, a compression of ar into the finished article is rendered unnecessary by adopting the expedient of forcing air into the article after it is placed in the mould, but before curing; the soft mixed rubber closing immediately on the minute hole which is necessary for this purpose.

The use of indiarubber for cleaning paper and erasing pencil-marks is a well-known application of the material, but its usefulness in this respect can be very much increased by incorporating certain gritty materials with it, such as pumice or finely divided-silica. Messrs. Wolff and Sons exhibit a collection of rubber specially prepared for these uses; and they have adopted the plan of mounting the rubber, squeegee fashion, in wooden blocks. By this arrangement, contact between the hand and the rubber is avoided. Some people let their erasing-rubber get very dirty, and then express surprise that it fails to clean paper.

Very pretty casts or mouldings of phototypic reliefs may be made in vulcanised indiarubber; and I will next illustrate to you the method of making such casts, at least as far as the manipulation of the caoutchouc is concerned. Here is an ordinary photographic negative, and this is a type-metal cast or mould, produced by photographic agencies from the negative. Those portions of the negative which are opaque correspond to relief in the typemetal mould, while the depressions of the mould correspond with the transparent portions of the negative.

The first step is to very slightly oil the mould, makes his rollers from red rubber, which is, of after which blacklead is applied to the surface, and necessity, very thoroughly cured, in order to the excess is polished off by means of a soft brush. enable it to withstand the action of fatty inks; and A sheet of mixed rubber, previously softened by after the rollers have been turned true by means of heat, is next applied to the prepared surface of the self-acting lathes, a fine surface is given to the mould, and curing is effected by means of the rubber by means of glass paper. In order to give small hot-press into which the mould and rubber his rollers the softness which is necessary in some are now placed. A hot-press of the kind now cases, Mr. Lanham now introduces a series of before you is very convenient for the curing of perforations parallel to the axis. For lithographic small flat articles and casts. It consists of a cast-printing, these rollers have very considerable adiron fish-kettle, upon the bottom of which rests a vantages over the usual leather roller, and some slab of type-metai an inch thick. Inside the kettle excellent samples of work done with them hang on is placed a small press, like a copying press in the walls.. Indiarubber does many services in miniature. By the side of the press stands a small connection with the art of printing, some of iron cup, containing glycerine, and in this fluid is these being of very great interest, but it is immersed the bulb of a thermometer, the stem of impossible to go farther into the matter this evewhich projects through a hole in the cover of the ning. kettle. By means of a small gas-stove, heat can be applied to the apparatus, and it is easy to so adjust the gas supply, that the thermometer shall indicate a tolerably constant temperature of, say, 140° or 150 Centigrade. Most qualities of mixed rubber will become fairly well cured by being heated under these circumstances for half to one hour, and any tendency towards adhesion to the mould is obviated by the preparation with oil and blacklead, as described.

This apparatus is extremely well adapted for curing the indiarubber stereotypes or stamps, which are now so extensively used for endorsement and other purposes. To make these stereotypes, a reverse or mould is made from the types, this being taken in plaster of Paris, or better still, in metal. When plaster is employed it is well to harden it, by saturating it with an alcoholic solution of shellac, and again drying. The soft mixed rubber is then forced into the mould, as you now see me doing it, after which the curing may be effected in the hot press.

Mr. John Leighton introduced rubber stereotypes about 18 years ago, and since that time their use has become very general for a great variety of purposes. Mr. Leighton has very kindly sent, for your inspection, an interesting collection of specimens, illustrative of the manifold uses to which indiarubber stereotypes can be applied. Glass and other hard bodies may be printed on with the greatest ease; and by dusting the impression with a vitrifiable colour, the impressions may be burnt in. Here are some of Mr. Leighton's specimens, illustrating what was done in this direction, as far back as ten years ago. Again, the rubber stamps lend themselves admirably to the production of impressions on curved or cylindrical bodies; this being illustrated by rocket cases, printed under Mr. Leighton's directions twelve years since. Much ingenuity is displayed in the construction of the various self-inking pocket and pencil stamps.

of old rubber in making the admirable floor-eloth known as kamptalicon, is a very useful application of it. Kamptulicon consists of old rubber and cork, both materials being brought into a state of fine division, after which they are incorporated by heated rollers, and then rolled out into sheets. You need not seek far for a specimen of this material, as the floor of this room is covered with it. The Britannia Rubber and Kamptulicon Company have lent me the figured and patterned specimens which are attached to the wall, and also other articles, which illustrate the various uses of this material. Knife-cleaning boards are often covered with it; and when made up into sheets, two inches thick, it is extensively employed as a means of deadening the effects of concussion. These thick sheets are particularly adapted for covering Waterproof goods, consisting of a thin layer of the floors of riding schools, or for lining cells in rubber spread on a textile fabric, are very exten-which violent lunatics are confined. sively made use of for the fabrication of overcoats, and other waterproof garments. In the manufacture of these goods, the first step is to prepare a dough or paste suitable for spreading on the material. If the vulcanisation of the coating is to be effected by means of steam heat, as in the case of cotton or linen goods, a composition of the following nature may be spread on the fabric:-201b. washed rubber, 20lb. zinc white, 5lb. sulphur, 61b. or 8lb. of solvent naphtha. When, on the other hand, the curing is to be performed by the cold process, the sulphur may be omitted. After the rubber has been softened by the absorption of the solvent naphtha, the materials are thoroughly incorporated by means of a mixing or kneading machine.

A very good illustration of the action of a spreading machine is afforded by the model which is now before you. It consists of a baseboard over which is supported a rule-like bar. The material to be coated is placed under the bar, a quantity of the paste or dough is piled up in front of the bar, and the cloth is drawn forward so that the rule or bar cuts off an even layer of the soft mixture. In actual practice, the fabric, after having received a coating of the composition, is passed over a heated steam-chest in order to dry off the solvent naphtha. In the case of ordinary goods, about six coats are given-three in each direction. Each coat may be estimated as being about one hundredth of an inch in thickness.

The method of applying the mixture of carbon disulphide and chloride of sulphur used for effecting the cold vulcanisation of the indiarubber coating, when spread on goods which would be injured by high-pressure steam, is of some interest. The coated fabric passes round a roller, coated side being outwards, and at the point, it is brought into contact with a more rapidly revolving slate roller, which dips in the vulcanising solution, this being I, for one, believe that the time will come when contained in a trough. The solution, which consists newspapers and books will be largely printed from of 1 part of chloride of sulphur, and 40 parts of carbon indiarabber stereotypes. They can be easily and disulphide, is led upwards by the roller towards a rapidly made, and I have cured rubber very point where it forins a kind of accumulation or successfully in the usual paper 66 or flong wave. All excess drains back. moulds, faced with tin or lead foil, this latter being laid first on the type. The steam-press might be employed for curing a rubber stereotype much larger than anything yet attempted in metal: and by employing a suitable rubber composition, it is not unlikely that a thorough curing might be effected in as short a time as ten or fifteen minutes. The power requ red to drive printing machines, working with rubber stereotypes, would be comparatively small, while impressions quite as sharp as those from metal ought to be secured. One advantage of the rubber stereotypes would be the ease with which they can be adapted to cylinders of any curvature. As regards ink for stereotypes a few words may be said. A fatty ink naturally injures the rubber; at any rate, if it is not very carefully removed after use; but an ink having glycerine as a basis answers extremely well, and may, as the specimens on the table prove, be left in contact with the stamps without in any way injuring them.

Inking rollers made of indiarubber have been Occasionally made use of from time to time for many years, but owing to inexperience in their manufacture and use, the results have been, until quite recently, far from satisfactory. You will probably remember that, when lecturing here on photo-mechanical printing, I showed you how a printing roller could be made with a body of the usual soft gelatiue composition, and a face of red vulcanised rubber, smoothed by means of glass paper. This circumstance brought to my knowledge the fact that Mr. Robert Lanham had been very successfully labouring in the improvement of indiarubber rollers. By the kindness of Mr. Lanham I was enabled to show you some of his rollers at the lecture immediately following the occasion when I showed you my own. During the two years which have lapsed since that time, Mr. Lanham has still further developed the manufacture of rubber rollers for printing purposes, and I am indebted to him for the opportunity of now showing you the very fine collection of these articles which stand over yonder. Mr. Lanham

t

Double-texture fabrics can be produced by employing similar apparatus, but double; and the two textures, which are vulcanised simultaneously, are brought into contact immediately after the curing solution has acted on them. Under these circumstances they adhere, but when made up into coats, &c., these double textures can be separated at the edges by the application of benzole; this being a matter of great convenience in joining the various parts of a garment together.

Spread goods are often varnished by the application of a dilute ammoniacal solution of shellac, the surface of the goods being generally prepared for the reception of this by the application of water, or of water containing a trace of an alkali, soap, or ox gall, either of which facilitates the adhesion of the lac varnish.

Spread sheets, already referred to several times, are made by spreading a mixture of sulphur (or other vulcanising material) and softened rubber on clothes previously charged with a mixture of paste, treacle, and glue. The required thickness having been built up, vulcanisation is effected by means of steam, and the prepared cloth, being softened by the action of water, can be easily removed fron the sheet of rubber. Sometimes the required thick ness of spread sheets is built up on two separate pieces of the prepared cloth, and the adhesive surfaces of the rubber being placed in contact, they unite, after which vulcanisation is effected in the usual way, and the cloths are removed. Spread sheets, prepared by the latter method, show the marking of the cloth on both sides, while those prepared by the first method are smooth on one side. As a general rule, spread sheets are more perfectly elastic than calendered sheets, as the rubber undergoes less mechanical tearing or dete rioration. They are generally preferred for cutting into threads.

Several processes have been proposed for the desulphurisation of old vulcanised caoutchouc, but the success attending endeavours of this kind has been very limited. The incorporation of old rubber with new has been referred to already. The use

ELECTRIC EXPANSION.

AN important research on the subject of electric

expansion has been lately described to the Berlin Academy by Prof. Quincke. The following is the summary of the author's results, as given in the current number (8) of Wiedemann's Annalen.

1. Solid and liquid bodies change their volume, when, like the glass of a Leyden jar, they are subjected to electric forces.

2. This change of volume is not due to heating, and is mostly an expansion. It may, however, Co of a contraction, as in the case, e.g., with fat oils.

3. In gases I have been unable to detect any change of volume through electric forces. If such occurs, it must be less than 1-3,000,000,000th of the original volume.

4. The change of volume occurs instantly in flint glass; but in longer time in Thuringian glass, which is a better conductor of electricity. In discharge of the coats of spherical or tubular condensers, the glass resumes nearly its original volume; instantly in the case of flint glass, mere slowly in that of Thuringian glass.

5. Simultaneously with the volume, length, also, of a tubular condenser is changed.

the

8. After discharge of the coats of a condenser, there remains a residuum in the sense of the original electric change of volume or elongation, which, in the case of flint-glass is very small, in that of Thuringian glass is large, and which appears to depend on the electric polarisation of the glass mass.

9. The change of volume and length is not due to an electric compression of the insulating substance.

10. In flint-glass, the electric expansion oecurs in all directions uniformly, like expansion through rise of temperature, independently of the size and direction of the electric forces.

11. Electric change of volume and elongation increase, in the case of glass, nearly in the same way, with rise of temperature, as the dielectric constants on the electric continuity of glass.

12. Under the influence of electric forces, the elasticity of flint glass, Thuringiau glass, and caoutchouc, decreases; that of mica and guttapercha increases.

13. The electric perforation of glass and other substances is a consequence of the unequal electric dilatation at different parts of the insulator.

and liquid substances may be irregularly dilated,
14. Through unequal electric expansion, solid
and become optically doubly refractive, just as
through unequal accession of heat, solid and I quid
transparent substances are unequally dilated, and
become doubly refractive.

shows no electric double refraction.
15. Glass uniformly dilated by electric forces

16. The behaviour of substances with "positive" and "negative" electric double refraction, to which Dr. Kerr has first directed notice, is explained by the way in which the various substances change the indices of refraction with density and volume, under the influence of electric forces.

17. With constant difference of potential of the coats of a condenser, the electric force, after discharge, is a long time of different amount in different layers of the insulating substance, at any given time, or in the same part of the insulating substance at different times.