Scientific American Supplement, No. 430, March 29, 1884

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The church deserves a few words, as it is a veritable cathedral as to
size and grandeur. The choir is immensely lofty, and constructed of
granite most elaborately wrought in the later Gothic or flamboyant
style. The nave and transepts are in the old Romanesque style, with
solid pillars and low round arches. The church is beautifully kept, and
contains some very interesting old reredoses and altars with carving in
alabaster. The one modern altar in the Lady Chapel is composed entirely
of silver! Our space will not permit us to describe the numerous
interesting old Abbey buildings--the library, the prior's lodging, the
vast kitchen, the prisons, the dungeons, and the means of supplying the
place in times of siege. The proposed causeway would join the island to
the left of our view, and our readers can imagine the abominable effect
of a high embankment disfiguring this point, and breaking through the
interesting old walls and towers, with, perhaps, a Brummagem Gothic
station against the old time-worn gateway.--_H. W. Brewer, in London
Graphic_.

* * * * *

ADORNMENTS OF THE NEW POST OFFICE AT LEIPZIG.

The cuts given herewith, taken from the _Illustrirte Zeitung_, represent
two statues for the new Post Office at Leipzig. The sculptor, Kaffsack,
has represented the post and the telegraph as winged female figures. The
figure representing Mail holds a horn or trumpet in her left hand, and
a letter in her right hand. The figure representing Telegraphy holds a
bunch of thunderbolts in her left hand, and unrolls a band for receiving
dispatches with her right hand. It will be observed that the figure
representing Telegraphy is made much lighter and more graceful than the
figure representing Mail, and has also a more energetic expression of
countenance, thus indicating the greater speed of Telegraphy.

[Illustration: ADORNMENTS OF THE NEW POST OFFICE, LEIPZIG, GERMANY.]

* * * * *

COAL GAS AS A LABOR-SAVING AGENT IN MECHANICAL TRADES.

By THOMAS FLETCHER, F.C.S.

Gas, as a fuel, is an absolute necessity to the economical carrying out
of many commercial processes. It is often used in the crudest and most
costly way; a burner may be perfect for one purpose, yet exceedingly
wasteful for another, and however good it may be, an error of judgment
in its application may lead to its total condemnation. An excess of
chimney draught, in cases where a flue is necessary, may pull in
sufficient excess of cold air to almost neutralize the whole power of
the burner, unless a damper is used with judgment. With solid fuel, an
excess of draught causes more fuel to be burnt, but with gas the fuel
is adjusted and limited; there is no margin or store of fuel ready to
combine with the excess of air, which, therefore, lowers the amount
of work done by its cooling power. The power of any burner, for any
specified purpose, depends not only on its perfection, but to a far
greater extent on the difference in the temperature of the flame and of
the object to be heated. For instance, if a bright red heat is required,
it is not possible to obtain this temperature economically with any
burner working without an artificial blast of air; the difference
between the temperature of the flame and that of the object heated is
too little to enable the heat to be taken up freely or quickly, and
the result is a large loss of costly fuel. If we want to obtain high
temperatures economically, an artificial blast of air is necessary,
and the heavier the pressure of air, the greater the economy. On the
contrary, low temperatures and diffused heat are obtained best by flames
without any artificial air supply.

For such purposes as ovens, disinfecting chambers, japanners' stoves,
founders' core drying, and similar requirements the best results are
obtained by a number of separate jets of flame at the lowest part of the
inclosed space, and the use of either illuminating or blue flames is a
matter of no importance, as the total amount of heated air from either
character of flame is the same. If there is any preference, it may be
given to illuminating flames, as the proportion of radiant heat is
greater, and this makes the average temperature of the inclosed space
more equal; but on the other hand, may be considered the greater
liability of the very fine holes, necessary for illuminating flames, to
be choked with dust and dirt. This may, to a great exent, be obviated
by using very small union jets, and setting them horizontally, so as
to make a flat horizontal sheet of flame. Burners placed this way are
practically safe from the interference of falling dust or dirt, but not
from splashes. Falling dirt or splashes must always be considered in the
arrangement of any burners, and the ventilation must be no greater than
is absolutely necessary for the required work. In cooking, this limit
of ventilation may be exceeded, as most things are better cooked with a
free ventilation, the extra cost of fuel being well compensated for by
the better quality of the result.

The air in an oven or inclosed space heated by flames inside is similar
in character to highly superheated steam. It contains a large proportion
of moisture, and yet has the power of drying any substance which is
heated to near its own temperature. A mass of cold metal placed in
the oven is instantly bedewed with moisture, which dries up as the
temperature of the metal rises. This is, for many purposes, an
objection, and the remedy is to close the bottom of the oven and place
burners underneath. If for drying purposes and a current of air is
necessary, the simplest way is to place in the bottom of oven the a
number of tubes hanging downward in such a position that the heat of the
flame acts both on the bottom of the oven and the sides of the tubes,
which, of course, must be long enough for the lower opening to be well
below the level of the flame. The exit may be at any level, but for
drying purposes it is better at the top, and it should be controlled
by a damper to prevent cooling by excessive currents of air. If not
otherwise objectionable, the arrangement of flames inside the oven is
far the most economical in use.

Where an oven or drying chamber is used continuously, it should be
jacketed with slag wool or boiler composition, but for many purposes
this is no advantage. As an example both ways, I will instance the
drying of founders' cores where there is only one blow per day. The
cores of an ordinary foundry can be dried by gas in a common sheet iron
even in about half an hour; any accumulation of heat after that time
would be useless, and a jacketed oven would be of no advantage.

For the disinfection of clothes in vagrant wards and hospitals for
infectious diseases, on the contrary, a continued heat is necessary, and
in this case the accumulation of reserve heat, which takes place slowly
in a jacketed oven, becomes of value, as the gas can be turned low or
out, and the ventilators closed, insuring a more complete disinfection
with a much smaller gas consumption. Where an oven or heated chamber is
much used for periods of over half an hour at once, a non-conducting
casing pays well by reduced gas consumption.

For albumen and glue drying, leather enameling, tobacco drying, and
purposes where a large space has to be very slightly and equally warmed
when the weather is unfavorable, steam-pipes are generally used, but,
not being always available, an exceedingly good arrangement may be made
by placing at intervals in the room gas burners, of any construction,
close to the floor, and surrounded with a sheet-iron cylinder, say 2 ft.
or 3 ft. high. The top of these cylinders must be connected throughout
with a fairly large flue, which will take the products of combustion
from the whole, and this flue must be carried either horizontally, or
with a slight rise, so as to utilize all the waste heat. The reason for
having a number of stoves at intervals is that the heat in a flue will
not carry, for any useful purpose, more than about 8 ft. or 10 ft., and
a single stove would give an irregular temperature in any except a very
small room. If all are not used at once, the flues of those not in use
may be closed by a damper to prevent down draught. The use of hot water
pipes heated by gas may also be occasionally advisable, but, unless for
some special reason, it is much more economical to use coal or coke, as
the bulk of water makes an exceedingly good regulator, and makes a fire
practically as steady and reliable as gas, thus superseding the more
costly fuel.

For one of my own purposes I need hot-water pipes, having very little
variation in temperature night and day; and using coke for economy's
sake, I get a regular temperature by heating a large quantity of water,
about 200 gallons, with the fire, and inclosing this in a tank jacketed
with slag wool. My circulating pipes run from this tank, and a
practically steady temperature, night and day, can be obtained with the
most irregular firing, and occasional extinction of the fire for several
hours at once.

For the heating of liquids, the greatest economy is to be obtained
from one single flame, of as high a temperature as can conveniently be
obtained, and the flame must be in actual contact with the vessel to be
heated. In jacketing vessels, to prevent draughts, care must be taken
that the jackets do not cause currents of cold air to rise rapidly up
the sides of the vessel, and so cool it. If this is the case, the use of
a jacket, instead of being an economy, is a positive expense, and waste
of heat. Many processes, such as making oil and turpentine varnishes,
require a heat under instant control, and in these the use of gas is an
important matter, as the loss and risk of fire are very serious elements
of expense, more especially in small works where special and costly
preparations for contingencies cannot be afforded. I have here a burner
which, for its power, is, perhaps, the most compact and gives the
highest temperature of any burner yet known, and it is easily made in
almost any size; it has, I think, many special advantages. The use of
gauze, which is its only weak point, is more than compensated for by the
very high duties obtained in practice with it, owing to the compactness
and concentration of the heat obtained. The following extract from my
communication to the Gas Institute will give all particulars as to the
constructive detail of this burner. Those who wish to go further into
the matter will find the paper referred to in the publication of the
Gas Institute for the current year, and also in the _Journal of Gas
Lighting_, June 26, 1883, and the _Review of Gas and Water Engineering_,
June 16, 1883.

"The first and most important part is the mixing chamber or tube, one
end of which is supplied separately with gas and air, which at the other
end are, or should be, delivered as a perfect mixture. It may be taken
as a rule that this tube, if horizontal, should not be less in length
than four and a half times or more than six times its diameter. It is
a common practice to diminish or make conical-shaped tubes. All my
experience goes to prove that, excepting a very trifling allowance for
friction, the area of the smallest part of the tube rules the power, the
value of the mixing-tube being no more than that of the smallest part.
If the mixing-tube is upright, new sources of interference comes in;
notably the varying specific gravity of the mixture. Except with one
definite gas supply, the result is always more or less imperfect, and
regular proportions cannot be obtained. This is now so well known that
the upright form has been practically discarded for many years, and
is now only used where the peculiar necessities of the case give some
special advantage.

[Illustration: Fig. 1. SPECIAL HIGH POWER BURNER. SHEWING ATTACHMENT B
WHEN USED WITH A BLAST OF AIR]

"The diameter of the mixing tube is a matter of importance, as it
rules the quantity of gas which can be satisfactorily burnt in any
arrangement. With large flames, given a certain size of gas-jet, the
diameter of the mixing-tube should be not less than ten times as great.
For instance, at 1 inch pressure, a jet having a bore of 1/8 inch will
pass about 20 cubic feet of gas per hour. To burn this quantity of gas,
a mixing tube is necessary 10/8 or 11/4 inch in diameter. By the first
rule this tube must be in length equal to four and a half times its
diameter, or 5-5/8 inches. It would appear that the mixing-tube, having
100 times the area of the gas jet, is out of all proportion to the size
necessary for obtaining a mixture of one of gas to nine or ten of air;
but it must be remembered that the gas is supplied under pressure. It is
therefore evident that no mere calculation of areas can be taken,
into account, unless the difference in pressure of the supply is also
considered. A complete reversal of this law is shown in that ruling the
construction of blowpipes, which I have already given in a previous
paper on 'The Use and Construction of the Blowpipe.' In these the air
supply, being under a heavier pressure, is much smaller in area than
the gas inlet; and, to obtain maximum power, the air-jet requires to be
enlarged in proportion to the gas pressure.

"Given a certain area of tube delivering a combustible mixture, the
outlet for this mixture must be neither more nor less than the size of
the tube. Taking an ordinary drilled tube, such as is commonly made, and
of the dimensions before given--i. e., 11/4 inch bore--if the holes are
drilled 1/8 inch in diameter the tube will supply 10 x 10 = 100 of these
holes. In practice this rule may be modified.

"The variations from the rule, however, must be a matter of experience
with each form of burner. There is also the fact that with small divided
flames it is not necessary to mix so large a proportion of air, as each
flame will take up air, on its external surface; but in this case the
flames are longer, hollow, and of lower temperature. As a matter of
actual practice, where a burner is used which gives a number of flames
or jets, the diameter of the mixing-tube does not need to exceed eight
times the diameter of the gas jet; the remainder of the air required
being taken up by the surfaces of the flames.

"Wire gauze, made of wire the thickness of 22 iron wire gauge, 20 wires
to the linear inch, and tinned after weaving, has an area in the holes
of 1/4 its surface. By calculation, the area of a gauze surface in a
burner should, therefore, be taken at four times that of the tube, and
our standard of 11/4 inch tube requires a gauze surface of 21/2 inches in
diameter. This rule is subject to variation in burners of a small size,
owing to the air that can, if required, be taken up by the external
surface of the flame, which, of course, is much greater in proportion in
a small flame than in a large one. Where the diameter of the gauze is,
say, not over one or two inches, the theoretical maximum gas supply may
be exceeded, and a varying compensation is necessary with each size.
My rule is intended to apply to burners of larger diameters, where the
external air supply plays a comparatively unimportant part.

[Illustration: Fig. 2.]

"It must be remembered that burners of this class, which burn without
the necessity of an external air supply in a flame which is solid,
require the mixture to be correct in proportions. A very slight
variation makes an imperfect flame. Not only does the gas jet require
to be adjusted with great precision, but it also needs more or less
adjustment for different qualities of gas. An ordinary hollow or divided
flame is able to take up on its surface any deficiency of air supply;
but with the high power solid flames the outside surface is small, and
the consequence is that one of these burners, adjusted for gas of poor
quality, may, when used with rich gas, give a long hollow or smoky
flame, unless the gas jet be reduced in size. When perfect, the flame
shows a film of green on the surface of the gauze; and if a richer gas
is used, the green film lifts away. To cause this to fall again, and to
produce a solid flame, it is necessary to take out the gas jet, and
tap the end with a hammer until, on trial, it is found correct. If too
small, the green film lies so closely as to make the gauze red hot.
Where the 'tailing up' of the carbonic oxide flame is objectionable,
there is no practical difficulty whatever in constructing these burners
as a ring, with an air supply in the center, which greatly reduces the
length of the 'tail.' In practice it is a decided advantage to have a
center air-way in all burners of more than about 2 in. diameter, as it
enables the injecting tube to be slightly shortened, and lessens the
liability of the green film to lift with varying qualities of gas. In
this class of burner I have adopted the small central air-way as a
decided improvement in the burners."

In such processes as the roasting of coffee, chiccory, grain, etc., a
diffused heat is necessary, but of much greater intensity than can be
obtained with economy from heated air. In these cases the application of
a direct flame is necessary, and it may be in actual contact with the
substances to be heated, provided these are kept in constant and rapid
motion.

The use of a revolving cylinder brings in complications with any burner
which is supplied with gas at ordinary pressures without any artificial
air supply, as the currents of air caused by the motion of the cylinder
interfere with the satisfactory working of any burner; and the air
supply must be either protected from draughts and irregular air
currents, or the air must be applied artificially from some independent
source. One exceedingly good way of making any burner work,
independently of the currents caused by a revolving cylinder, is to
apply the flame inside the cylinder at the center, making the substances
to be heated to fall in a continuous stream through the flame. This
system is not applicable to fine powders or sticky substances, as it
necessitates the perforation of the cylinder, to allow of the escape of
products of combustion.

For this class of work, a very concentrated heat is not desirable, as a
rule, and a slit or a perforated burner is preferable. Of this class of
burner I have here a sample, which is not only new in its constructive
details, but has great and special advantages for many purposes. As
you see, it resembles a number of ordinary furnace bars, with this
difference, that each bar is a burner; in fact, it is an ordinary
furnace grate, which supplies its own fuel. With the usual day pressure
of gas=1 inch of water, this burner will, at its maximum power, consume
about 100 cubic feet of gas per hour per square foot of burner surface,
and as it can readily be made almost any form or size, its adaptability
for a great number of uses is evident. I have made it in many sizes and
shapes, to give flames from 1/2 inch wide by 5 feet long to large square
or oblong blocks. By applying a blast of air at the ordinary gas jets,
and supplying the gas by a separate pipe, or series of pipes, below
the open end of the burner, this can be converted into a furnace of
extraordinary power. It is quite possible to burn as much as 2,000 cubic
feet of gas per hour per square foot of burner surface, producing a heat
sufficient to fuse any ordinary crucible. You see its power when I place
a bundle of iron wire in the flame; it is, in fact, a concentration of
hundreds or thousands of powerful blowpipe flames in one mass. It has
also this advantage, that with a blast of air it will burn and work
equally well any side up, and the flames can therefore be directed
straight on their work without loss. It is, in one form or another,
almost a universal burner, as it can be readily adapted to almost any
purpose, from tempering a row of needles to making steam for a 200 horse
power steam engine. It is easy to make, easy to manage, practically
indestructible, and for commercial purposes has, I think, a general
adaptability which will bring it, in one form or another, into almost
universal use. I may say that when we are in a special fix, this has in
every case landed us out of the difficulty.

For heating large plates of metal equally, for drying paper impressions
for stereotypers, hot pressing hosiery, crumpet baking, working up
plastic masses which can only be worked hot, and work of this class, a
number of separate flames equally diffused under the whole surface of
the plate are necessary to equalize the heat, unless the plate is very
thick, and these are better if produced by a mixture of gas and air; but
in heating wide plates one difficulty must always be remembered, the
burnt gases from the center flames can only escape by passing over the
outer flames, and therefore a space must be left between the top of the
flame and the plate, or the outer flames will be smothered and make a
most offensive smell.

In hosiery presses, printers' arming presses, and many others, the top
plate also requires to be heated. The best way to do this is to use a
number of blowpipe flames directed downward. In many cases the supply
of air under pressure is a practical difficulty and objection. This is
overcome, to a certain extent, by the use of a thick upper plate with a
number of horizontal holes, into which a Bunsen flame is directed. In
every case I have seen, without one single exception, the holes are
either too small, or the burner is placed too close, and the consequence
is that the gas, instead of burning inside the holes, as it should,
passes through partially unburnt, and is consumed at the opposite end,
where it is absolutely useless, the flame not being in contact with or
under the surface to be heated, and therefore doing no work. In hosiery
presses this is a great objection, as the holes are so long that an
equal heat is simply impossible, and the only remedy is to use a
blowpipe flame, which forces sufficient air in with the gas to insure
combustion where the heat is necessary. The same remark applies to crape
and embossing rollers.

For the production of heat in confined spaces and difficult position,
the use of an artificial blast of air is becoming an acknowledged
necessity, and the small Roots blowers now made for such purposes, and
driven by power, are coming rapidly into use.

Sometimes a plate is required to be heated to a high temperature in one
confined spot, and, as an example of this, I may take the bluing of the
hands of watches. For this purpose I have made several arrangements,
and perhaps the best is a thin copper plate, bent down at one side to a
right angle. In this angle, underneath, is directed a very fine blowpipe
flame on one spot, and the hands are passed singly over this spot until
the color comes, when they are instantly pushed over the edge. I have
here the arrangement which is generally used for this purpose. For the
bluing of clock hands, a larger and more equally heated surface is
required, and this can be obtained by a small powerful burner without
a blast of air, using a rather thicker plate to equalize the heat. The
same arrangement may be used with advantage for tempering small cutters
for ornamental turning, penknife-blades, etc., and in these cases the
cooler part of the plate is of great value, as it enables the thicker
parts to be slowly and equally heated up; the application of a
mechanical arrangement to pass the articles to be heated in a regular
succession is a matter easily managed.

[Illustration: FIG. 3. BLUEING WATCH HANDS & TEMPERING SMALL TOOLS]

Among other things which have several times come under my notice may be
mentioned cremation furnaces, but I have not yet met, with, or been
able to devise, any burner for ordinary coal gas which has worked
satisfactorily. This fuel is apparently unfitted for the work, and
the best arrangement I know is a number of pipes delivering ordinary
"producer" gas from the Wilson or Dowson generators, in exactly the
same way as is at present used for firing horizontal steam boilers. For
heating book finishers' tools, a ring-flame is the simplest, the tools
being supported a little distance above the flame; the usual plan of
heating a plate, and placing the ends of the tools on this, necessitates
at least double the gas consumption as compared with an open flame.
For type-founding machines, bullet moulding, stereotype metal melting,
solder making, lead melting, etc., one burner, or rather one flame,
should be used of a suitable power for the work, and this should be as
perfect and of as high a temperature as possible to insure economy. It
is now a simple matter, owing to recent researches in the theory of
heating burners, to obtain flames of any power without practical limit,
which, without any artificial air supply, will do all which is necessary
in this class of work, and the required arrangements are exceedingly
simple. With these trades may be classed, also, the concentration and
distillation of acids and liquids boiling at a high temperature, and we
may also include baths for tinning small articles, and the tinning by
fusion of sheet copper, the same burners being applicable, and perfectly
suited to all these requirements, unless the tinning baths are long and
narrow, in which case the furnace-bar burners again come to the front as
the best; as, if we are to use gas economically, the flame must be the
same shape as the vessel to be treated.

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