IMPROVEMENTS IN GLASS FURNACES
Year: 1861

page_text: LETTERS PATENT to Charles Schinz, of Offenburg, in the Grand Duchy
of Baden, Engineer, for the Invention of "IMPROVEMENTS IN GLASS
FURNACES."
Sealed the 31st January 1862, and dated the 3rd August 1861.
PROVISIONAL SPECIFICATION left by the said Charles Schinz at the
Office of the Commissioners of Patents, with his Petition, on the 3rd
August 1861.
I, CHARLES SCHINZ, of Offenburg, in the Grand Duchy of Baden, Engineer,
do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
GLASS FURNACES," to be as follows:-
The nature of my Invention consist in the peculiar construction and
arrangement of the various parts composing or forming the glass furnace, and
in the mode of supplying atmospheric air under pressure to the fire in the
grate, and also to the combustible gases and other products generated by
such fire, whereby a considerable saving in fuel and an entire absence of
smoke and dust is obtained. The fire grate forms part of a separate furnace,
which I call the "gas generator," and this grate, which has an inclined position,
is fed through a hopper with coal or other fuel. For the production of the
gases from such fuel, as well as for their combustion, I inject heated air by

page_text: means of a fan into the gas generator and into the furnace, and the supply
of air is by means of valves and pressure gauges so regulated as to furnish
the exact quantity necessary to ensure the perfect combustion of the gases.
From the generator the gases pass to the furnace holding the pot or pots
or crucibles, where being mixed with air as stated they burn with great
intensity. I prefer to place only one or two pots into one furnace and to
make the pots of an oblong form, flat on two sides and rounded at both
ends or at the corners. The furnace corresponds in shape with that of the
pot or pots, and as only a limited space is allowed between the sides of the
pot and the walls or sides of the furnace, the flames are forced to strike or
impinge upon the sides, and lastly to pass over the top of the pots through
flues or pipes to the shaft. These pipes pass through one or more air
chambers thus heating the air supplied for combustion by the fan. The
surplus heat from the furnace may also be used for heating annealing furnaces
and the like. The furnaces are built of a material which in the process of its
manufacture is rendered porous and into a bad conductor of heat. As above
-stated-my-improved-glass- furnaces_may_be_heated with coal or with other
fuel, but they are particularly adapted for coal, the use of which is the most
economical. My improved glass furnaces also offer peculiar advantages in
the working of the pots, being accessible at the part opposite to and removed
from the fire-grate. When more than two pots are required I prefer to
build or join on a new generator and furnace for each additional pot or pair
of pots, thus forming a row of furnaces. Owing to the perfect combustion
and consequent entire absence of all smoke and dust and other impurities the
glass produced is of a superior quality and the pots do not require to be made
with tons or hoods.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Charles Schinz in the Great Seal Patent Office on the
3rd February 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, CHARLES
SCHINZ, of Offenburg, in the Grand Duchy of Baden, Engineer, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Third day of August, in the year of our Lord
-One thousand eight hundred and sixty-one, in the twenty-fifth year of Her
reign, did, for Ierself, Her heirs and successors, give and grant unto me, the

page_text: said Charles Schinz, Her special licence that, I, the said Charles Schinz, my
executors, administrators, and assigns, or such others as I, the said Charles
Schinz, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might make, use, exercise,
and vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN
GLASS FURNACES," upon the condition (amongst others) that I, the said
Charles Schinz, my executors or administrators, by an instrument in writing
under my, or their, or one of their hands and seals, should particularly
describe and ascertain the nature of the said Invention, and in what manner
the same was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar months next and immediately after
the date of the said Letters Patent.
NOW KNOW YE, that I, the said Charles Schinz, do hereby declare the
nature of my said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
The nature of my Invention consists in the peculiar construction and
arrangement of the various parts composing or forming the glass furnace,
and in the mode of supplying atmospheric air under pressure to the
fire in the grate, and also to the combustible gases and products gene-
rated by such fire, whereby a considerable saving in fuel and an entire
absence of smoke and dust is obtained. The fire grate forms part of a
separate furnace which I call the "gass generator," and this grate, which
has an inclined position, if intended for burning coal, is fed through a hopper.
For the better production of the gases, as well as for their subsequent
combustion, I inject atmospheric air by means of a fan into the gas generator
from beneath, and heated air into the flue leading from the fire grate or
generator to that part of the furnace holding the pot or pots, and the supply
of air is so regulated as to furnish the exact quantity necessary to ensure
the perfect combustion of the gases. From the generator the gases pass
to the furnace holding the pot or pots or crucibles, where being mixed with
air as stated, they burn with great intensity. I prefer to place only one
or two pots into one furnace and to make the pots of an oblong form, flat
on three sides and rounded at one end and at the corners. The furnace
corresponds in shape with that of the pot or pots, and as only a limited
space is allowed between the side of the pot and the walls or sides of the

page_text: furnace; the flames are forced to strike or impinge upon the sides of the
pots, and lastly to pass over them and from thence through flues or pipes
to the shaft. These pipes pass through one or more air chambers where
they heat the air supplied for combustion by the fan. The surplus heat
from the furnace may also be used for heating annealing furnaces and the
like. The furnaces are built of a material, which, in the process of its
manufacture is rendered porous and into a bad conductor of heat. As above
stated my improved glass furnaces may be heated with coal or with other fuel,
but they are particularly adapted for coal, the use of which is the most
economical.
In order that my said Invention may be more fully understood, I will now
proceed to describe the same, reference being had to the annexed Sheet of
Drawings, and to the letters and figures marked thereon.
Fig. 1 is a longitudinal vertical section through the line A, B, of Fig. 2;
Fig. 2 is a transverse vertical section through the line C, D, of Fig. 1; Fig. 3
is a transverse vertical section through the line I, K, of Fig. 1; Fig. 4 is a
transverse-vertical_section through the line L, M, of Fig. 1; Fig. 5 is a
horizontal section through the line E, F, of Fig. 1,-and-Fig. 6 is a horizontal
section through the line G, H, of Fig. 3. In this furnace the fuel is intro-
duced into the hoppers M, M, which are provided at the top with a closely
fitting lid, and at the lower end with a conical valve, through which the
coal is from time to time caused to descend into the shaft or funnel L, which
serves as a reservoir, and from thence upon the slanting grate J. The air
which is necessary to effect combustion being forced by means of a fan
or otherwise through the flue N into the chamber under the grate as well
as into the air chamber Q, and through the passage O, and uptake flues P, P,
respectively. The gases which are evolved from the fuel ascend through
the passages G, G, and on arriving in the combustion chambers B, B, B,
they are supplied through three sets of treble tuyeres X, X, X, which are
in communication with three chambers C, C, C, and tubes or pipes E, E, E,
with the requisite quantity of air previously heated in the chamber Q. These
combustion chambers are a most important feature of the apparatus, and
as it is there that the combustion of the gases has to be effected, and it
being most important that the combustion should be complete, they must
be of sufficient length and of a suitable section. Generally I make them
two feet in length and the section such that the mixture of gas and air is
formed under a certain pressure, say equal to a column of from 30 to 80 feet
of air. For only when under some pressure the gaseous fluids are brought

page_text: into full contact, so as to enter into combination. The admission of air
under the fire-grate can be regulated with the greatest precision by means
of a valve placed in the passage or flue O, and the supply of heated air to
the combustion chambers B, B, B, is likewise regulated by the slides F, F, F:
By these means the exact quantities of air which are required for the most
economical combustion of the fuel can be obtained, provided that the various
flues, passages, and chambers be made of the proper proportions and
dimensions, a subject to which I shall have occasion hereafter to refer at
some length.
The ingredients required for the production of glass are contained in the
crucibles A, A, which are placed in a separate chamber. The ignited gases
or hot products of combustion are forced along the sides of the crucibles, and
being deffected by the slanting door S, pass over them and through the outlets
T, T, into the retorts D, D, and chimneys U, U, by which means the air
contained in the chamber Q is heated to the required degree. It will be
observed that the ignited gases thus travel a distance equal to twice the length
of the crucible, plus the difference between the height of the crucibles and
that of the flue B. During the continuance of the smelting process the
working holes in the door S are kept closed, so as to compel the products of
combustion to pass through the openings T, T. When the time arrives for
converting the glass into the various articles for which it may be required
these holes are of course kept open; and if, during this latter period, the
pressure maintained in the furnace were the same as that which prevails
during the process of smelting, the products of combustion would escape
through the working holes and render the working difficult, if not impossible.
As in this case less heat is, however, required, the outlets T, T, and the
chimneys U, U, suffice to carry off the products of combustion, the draft being
regulated by means of dampers in the chimneys. Should it be considered
desirable to generate less heat during working time it would only be necessary
to lower the pressure of the air. By allowing a trifling excess of gas to be
ignited by a current of air passing in through the working holes, a beneficial
result is produced, as the glass is thereby prevented from becoming chilled on
the surface of the crucibles. The slides F are, as a general rule, to be kept
open, but the moment the blast is taken off they must be carefully closed,. as
otherwise some of the combustible gas might filter into the chambers C, and
from thence through the tubes or pipes E into the combustion chamber Q,
where its mixture with an excess of air might produce an explosion, not very
dangerous, indeed, but yet sufficiently powerful to do some injury to the
furnace. As the fuel contained in the reservoir L descends upon the grate

page_text: very slowly, and in proportion to its rate of consumption, a small portion of it
only is at any time subjected to the process of dry distillation, producing
vaporous compounds of carburetted hydrogen, which escape with the gas.
These compounds have a tendency to become decomposed in the higher tem-
perature they meet with beyond the gas-generation chamber H and in the
passages G, in which case they deposit a spongy coal which, after a time, is
apt to choke up the passages, and thereby to obstruct the free flow of the gas.
The most rational way of preventing such deposits from being formed is to
shorten as much as possible the distance over which these vaporous com-
pounds have to travel; and this is effected, as shown in the Drawing, by
bringing the generator H and the injectors X, X, X, close together. The
slow-and-regular production of these vapours, owing to the gradual descent of
the fuel from the reservoir I, likewise tends to diminish-the quantity of these
deposits and to render the composition of the gas uniform. Although, how-
ever, the means above-mentioned for preventing, or at all events greatly
diminishing such deposits, are very effectual, it may still happen that, after the
furnace has been in operation for some considerable time, a certain portion of
such deposits will-accumulate in the passages G; it is therefore important
that the means should be at hand for removing them without stopping-or
interrupting the operations. These means are afforded by the flue V, which
is open on both sides of the furnace, and from which three short passages W
lead into the passages G. On the carbonaceous deposits in the passages G
requiring to be removed, the flue V, which at all other times is closed, is
opened, and the supply of air under the grate J, is simultaneously stopped, or
nearly so. The result is that the production of gas is greatly diminished, that
the gas meets, from the passages W, with a supply of air in excess, and that
this excess of air consumes the carbonaceous deposit in the passages G in a
very short time.
Having now described the peculiar features and functions of my improved
furnace, I consider it necessary to point out its manifold advantages and to
explain the considerations and principles which have guided me in its design,
the main object of which is the attainment of the most perfect and economical
combustion of the fuel employed in the smelting of glass, as well as the appli-
cation of the greatest possible proportion of the heat produced to that purpose.
It is well known that any kind of fuel burnt on a grate, be it by means of the
simple draft of a chimney or by a blast, evolves certain gases, which take up
the heat produced by the combustion. But the quantity as well as the
intensity of the heat varies according to the quantity of air introduced. An
excess of air produces complete combustion, but the temperature of the gases

page_text: A
in that case is too low for any operation requiring an intense heat.
relatively deficient supply of air, on the contrary, produces a far higher
temperature, but the products of combustion in that case contain a certain
portion of oxide of carbon which escapes combination, and therefore the heat
is under those circumstances deficient as to quantity. By converting the fuel
in a separate chamber into combustible gases, and burning these afterwards
through the introduction of a fresh supply of heated air, the combustion
becomes very perfect; and as this process admits of the exact quantity of air
being mixed with the gases, it affords the means of raising the temperature of
the products of combustion to the highest degree of which the composition of
the fuel is susceptible. Thus, 1 lb. of coals produces, with an excess of air,
7509 units of heat, but a temperature of only 1409° C. The same quantity
of fuel burnt with an insufficient quantity of air produces only 5228 units
of heat, but the temperature of the products of combustion is increased to
2276° C. By consuming the same quantity in the shape of combustible
gases the quantity of heat produced will again become 7509 units, but the
temperature acquired is, in this case, 2687° C. The advantages which, this
latter mode of combustion offers are obvious. Its adaptation to glass furnaces
has been attempted by many, and various Patents have been obtained for the
process, but the results have, in every instance, been far short of what. they
ought to have been by comparison with the standard which the preceding
figures establish. In fact no striking economy has been realised, although a
saving of from 43 to 44 per cent. ought to have been effected, independently
of the higher temperature produced. This increased temperature of the
products of combustion, however, ought also to produce a very considerable
saving. The temperature of the furnace being, for instance, 1500° C., it is
evident that the products of combustion must be discharged from the furnace
at a temperature superior, or at least equal, but in no case inferior. Now the
specific capacity of heat of the products of combustion resulting from 1 lb. of
coal is 2.29734 for 1° of temperature, and assuming the combustion to be
incomplete, whereas this capacity is 2.82138 when the fuel has been pre-
viously converted into gas. The quantity of heat discharged in the first case is
1500X2 29734-3446 units of heat, and in the second case 1500 x 2.82138
4232 units; and the quantity of heat retained in the furnace in the
first case is 52283446 1782 units, whilst in the second it amounts to
75094232 3277 units, consequently a saving of about 84 per cent. ought
to be realised by the combustion of the gas. It might reasonably be expected
that the practical results would, to some considerable extent at least, agree

page_text: with those derived from the theoretical investigation of the subject, but such
has not hitherto been the case. The principal cause of this want of success
must be looked for in the fact that the perfected process of combustion has, so
far, been attempted to be applied to furnaces constructed upon the old system,
for which it is in no wise adapted. If in the one case 100 lbs. of fuel be
burnt, the consumption in the other ought to be but 16 lbs. The volumes of
the products of combustion at their proper temperatures are 85200 cub. ft. and
27120 cub. feet respectively, the volume in the second case being, therefore,
only about one-third of what it is in the first. If in reality a so much smaller
volume had to pass through the same space as the large volume-it would not
come into contact at all with the surface to be heated, but the current would
assume the shape of a flame produced by the blowpipe, and the contents of
the crucible-would-not-be.smelted at all. On the other hand, by increasing
the volume of the products of combustion to the saine extent, much of the
economical effect is necessarily lost, yet not to a sufficient extent to account for
there being no saving at all. In order that the above-mentioned temperature
of 2687° C. may be produced the quantity of air injected into the gas must be
exactly adjusted to the quality and quantity of the gas, otherwise the products
of combustion will contain either-an-excess of air or of gas, in both of which
cases the temperature would be lowered, and in the second even the quantity
of the resulting heat diminished, whence the amount of saving otherwise
attainable would be reduced. Now it is impossible to obtain this exact quan-
tity of air, even by using valves and registers, unless a careful record be kept
of its own pressure, of the resistance to be overcome in the furnace, and of the
velocity of the gas; and such complicated calculations had not been made,
and were rendered still more difficult by the products of combustion being
introduced below the furnace, since the draft produced in the furnace itself
acted upon these various elements.
A third cause, which frustrated all attempts at effecting an economical
combustion, and which is also owing to the usual form of glass smelting
furnaces, is the short distance through which the products of combustion have
to travel before they are discharged. Of course a current which begins with
a temperature of 2687° C. requires a larger surface to deposit heat enough to
cool it down to 1500° than a current which begins with a temperature of
2276° C. only. The surface being insufficient, or, what comes to the same
thing, the distance being too short, the products are discharged at a tem-
perature much above that of the furnace, whence must result a waste of
heat,

page_text: With a view to the removal of all these difficulties, and in order to realise all
the saving which theory indicates to be attainable, the following essential
points are attended to in the construction of my improved furnace :-
1stly, the space through which the current of the products of combustion
has to pass is calculated to suit the volume of air required.
==
2dly, to enable the person charged with the superintendence of the furnace
to admit the proper quantity of air for admixture with the gas, I use three
different means, viz.:-a. I produce in the furnace a certain resistance by
narrowing the openings by which the products of combustion have to escape
from the furnace. This resistance is expressed by the height of a column of
cold air, calculated in accordance with the rules given by me in my book
entitled "Die Heizung & Ventilation in Fabrik Gebacuden," and published at
Stuttgard in 1861. b. This resistance, supposed to be eighty feet, is multiplied
with the weight of the products of combustion which pass through in one
second of time. Assuming this weight, for argument's sake, to be 0.1 lb., the
product is equivalent to 8 lbs. raised 1 foot, or 0.1 lb. raised 80 ft. and it represents
the power to be developed by the air to be injected. If, now, the weight of air
required to be introduced should happen to be 0.07 lb., the corresponding pro-
pelling column would be represented by 0.87 = 114 feet; hence the velocity of
this volume of air would have to be √29x 114=√65-368 × 11486-3 feet;
and from this latter product the area of the air pipes has to be calculated.
The pressure of the air is indicated by a very sensitive gauge, and must be
constantly maintained at the point above mentioned by the superintendent,
who has the means of adjusting it within his reach. c. A constant and
uniform supply of air being thus maintained, the next and only thing required
is to generate the gas in the proper proportion. The quantity of gas depends
entirely upon the quantity of air introduced into the gas generator, in which a
comparatively small pressure is required. The air, as has been explained in
reference to the Drawing, is introduced through the main air flue N by means
of a valve to be opened or closed by means of a worm and worm wheel,
or a similar contrivance, and the position of which must be indicated by
suitable mechanism, so that the superintendent may be able to ascertain the
exact quantity of air injected. Supposing the quantity of air thus introduced
to be 0.1 lb. per second, this amounts to 360 lbs. per hour, and the cor-
responding weight of fuel to be converted into gas during the same time
would be 50.5 lbs. Now the quantity of fuel consumed in a given time can
be ascertained, and if this quantity agrees with the quantity of air injected
into the gas, the right proportion is found. Having marked the exact position

page_text: of the valve, which admits the desired quantity of air into the generator, we
have only to maintain it at that point in order to obtain almost invariably the
same result. The size of the fuel, as well as the clinkers, may occasion some
variation in the production of the gas, inasmuch as they effect the degree of
resistance opposed to the passage of the air; but these causes of obstruction
can be avoided by keeping the grate clean, and by giving it a large surface.
Moreover, a slight adjustment of the valve may safely be allowed to compensate
for such irregularities in the hands of an experienced superintendent. The gases
arrive in the combustion chamber B without any perceptible velocity if the
generator is nearly on a level with it. In some cases this arrangement may
happen not to be convenient, and under those circumstances, the velocity of
the gas must be taken into account in computing the propelling power
required.
3dly. In order to cause the products of combustion to travel over a sufficient
distance, I bring them into contact at first with the long sides of the crucible,
and then lead them-back-over-the-top of the crucible to the outlets T, T,
through which they are discharged. We have seen above, that of 7509-units
of heat produced, only 3277 units remain in the furnace, the remaining 4332
units being expelled. Of the 3277 units taken up by the furnace, one
portion is absorbed by the crucibles and their contents, and another portion
penetrates through the walls forming the furnace. These two quantities are
to each other, in the furnaces-of-the-ordinary.construction, nearly in the pro-
portion of 1 to 2, whilst, in the best of my furnaces hitherto constructed they
are as 9 to 10; but from the furnaces which are actually in progress, I expect
still better results. It is evident, that if all the heat which penetrates
the walls and doors of the furnace could be utilized, a great saving would be
effected. This is impossible; but if the quantity of heat thus lost could be
reduced to of that taken up by the furnace, an additional saving of 10%
beyond that effected by the improved process of combustion would be the
result.
The means by which I effect these additional savings are threefold, and
may be summed up as follows:-1st., reducing as much as possible the
surface with which the heat comes in contact, and this I accomplish by the
peculiar construction of my furnace; 2nd, preventing the heat from pene-
trating in large quantities by making the walls thick, or where this cannot
conveniently be done, by using refractive materials rendered highly porous by
the admixture of powdered charcoal, which is subsequently consumed in the
kiln; 3d, placing the outlets T, T, which are of oblong shape, nearly on a

page_text: level with the top of the crucibles, by which means the current is compelled
to pass closely over the surface of the crucibles, and prevented from coming
into forcible contact with the arch over head, so that it cannot become heated
to an injurious extent.
In reference to the retorts D, D, I would observe that they are made of
fire clay like the crucibles; I prefer to make them about 1 inch thick; and in
order that they may heat the air to 300° C. one square foot of surface is
required for every 4-7 lbs. of air to be heated if the products of combustion
are to be expelled at a temperature of 1500° C.; and it requires
5.2 lbs. of air if the discharge is to take place at 1600° C.
5-6 lbs. of air if the discharge is to take place at 1700° C..
6.0"
6.4”
"
"
و"
دو
"
1800°
1900°
"
"
2000°
وو
7.0"
"
"
"
This process of heating the air of course adds a certain quantity of heat to the
products of combustion. 1 lb. of air heated to 300° contains 300 x 0.2377=
71-31 units; and 1 lb. of air being required to burn the gas generated
by 0.14 lb. of coal, which produces by itself 0-14 × 7509=1051.26 units; the
total heat produced is 1122.57 units, and the temperature resulting therefrom
'
1122-57
=2842° C. This is probably the utmost temperature the
0.142.82138
materials of which the furnaces are constructed can resist, and to push it any
further would be to jeopardize the safety of the furnace.
If in the furnaces hitherto constructed the initial temperature of 2276° C.
has sufficed for the purpose of smelting glass, and the gas combustion process
now admits of its being raised to 2842° C., it does not follow that the average
temperature must needs exceed that which prevails in the old furnaces; and,
indeed it ought not to be greater if all that economy of fuel is to be effected
which I have shown to be attainable. But an increased temperature is and
may be desirable for two reasons, although it may produce less favorable
results in point of economy. First, the affining of the smelted glass is
performed more perfectly under the influence of a very intense heat; and,
secondly, an increased heat of the furnace may effect a saving of greater
importance in a pecuniary point of view, namely, a saving in the alkalis used
in the composition from which the glass is produced. For these reasons it is
desirable to heat the furnace to the highest temperature the materials of
which it is built can bear. This capacity to withstand the effects of a high
temperature would be much impaired if the air heating apparatus were as

page_text: .
usual made of iron, therefore its construction of refractive materials is a
collateral improvement.
Another improvement as regards the air heating apparatus consists in
confining the products of combustion in retorts, instead of such products
surrounding the retorts. For it is evident that in the latter case the walls of
the air chamber Q would be the means of transmitting a considerable quantity
of heat to the surrounding air. This arrangement, however, is only of
importance where the heat contained in the products of combustion is again
made available after these products have left the air heater. The products of
combustion can be and have been so applied; and it is another important
feature in connection with my improved furnaces that the waste heat may be
made available for various purposes, as the products of combustion can be
conveyed anywhere from the chimneys U, U, by producing the necessary draft.
I have thus used the waste heat for warming the materials from which the
glass is to be produced, for working annealing furnaces, and for drying wood
and other fuel.
I do not claim as my Invention either the process of first converting fuel
into inflammable gases, and then effecting their combustion, nor its application
to glass furnaces generally, as the former is already known, whilst the latter
has also been previously introduced, although without yielding satisfactory
results; but-what I do claim as the Invention to be secured to me by the
herein-before in part recited Letters Patent is,--
Firstly, making the area of the passages through which the products of
combustion have to pass proportionate to the volume of air required, as given
by calculation.
Secondly, producing in the furnace a certain resistance to the discharge of
the products of combustion by making the outlets narrow, this resistance being
represented by a column of cold air according to the rules laid down in my
book entitled "Die Heizung & Ventilation in Fabrik Gebacuden."
Thirdly, regulating the quantity of air introduced into the gas generator in
the manner and by the means herein-before described.
Fourthly, causing the products of combustion to pass along the sides of the
'crucibles, and to return over the tops thereof, as described, so as to utilize them
to the greatest possible extent.
Fifthly, reducing the surfaces of the flues as much as possible.
Sixthly, rendering the materials of which the walls of the furnace are
constructed porous by the admixture of charcoal.
Seventhly, placing the outlets for the products of combustion nearly

page_text: on a level with the crucibles, so as to prevent them from over heating
the arch.
Eighthly, bringing the gas generating chamber in close contiguity to the air
injecting chamber, so as to prevent or at least diminish the formation of car-
bonaceous deposits.
Ninthly, removing such carbonaceous deposits by the admission of air
through the passages V & W, as described.
Tenthly, making the air heating apparatus of refractive materials, so as to
admit of the furnace being heated to a higher degree.
Eleventhly, causing the products of combustion to pass through the retorts
in the air heating chamber instead of passing the air to be heated through the
retorts.
Twelfthly, utilizing the waste heat of the products of combustion.
In witness whereof, I, the said Charles Schinz, have hereunto set my
hand and seal, this Twenty-eighth day of January, in the year of
our Lord One thousand eight hundred and sixty-two.
CHS. SCHINZ. (L.S.)