IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN GLASS
Year: 1841

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, we, HENRY
BESSEMER, of Baxter House, St. Pancras, and CHARLES LOUIS SCHÖNBERG,
of Sidmouth Street, Gray's Inn Lane, in the County of Middlesex, send
greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Twenty-third day of September, in the fifth year of Her reign,
did, for Herself, Her heirs and successors, give and "grant unto us, the said
Henry Bessemer and Charles Louis Schönberg, Her especial licence, full
power, sole privilege and authority, that we, the said Henry Bessemer and
Charles Louis Schönberg, our executors, administrators, and assigns, or such
others as we, the said Henry Bessemer and Charles Louis Schönberg, our
executors, administrators, or assigns, should at any time agree with, and no
others, from time to time and at all times during the term of years therein
expressed, should and lawfully might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed, our Invention of
"IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN GLASS;" in which said Letters
Patent is contained a proviso that we, the said Henry Bessemer and Charles
Louis Schönberg, or one of us, shall cause a particular description of the nature
of our said Invention, and in what manner the same is to be performed, to be
inrolled in Her said Majesty's High Court of Chancery within six calendar
months next and immediately after the date of the said in part recited Letters
Patent, as in and by the same, reference being thereunto had, will more fully
and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, we, the said
Henry Bessemer and Charles Louis: Schönberg, do hereby declare the nature
of our said Invention to relate chiefly to an improved manufacture of those
descriptions of glass known by the names of plate glass and flint glass, for
optical purposes, and to consist,-
Firstly, in a new form of a refining furnace for the refining of plate glass,
whereby each melting cistern receives heat separately and at bottom, instead
of receiving it from the reverberatory arch common to each as at present
used, the form of which arch admit of what are technically called "tears" to
drop into the refining cisterns, which we obviate by forming the roof of each
furnace of a conical shape, at such an angle that the tears would run down and
drop outside the cisterns, and by which method we are enabled in the process
of refining to produce the "metal," as the glass is technically termed, in a
purer state for casting than by the present method, as a considerable portion
of the air which is mixed with the glass in the operation of lading from the
founding pot to the refining cisterns rises, to; the surface and escapes. The
principal defects, in the present method of applying heat in the process: of
refining, as before described, are as follows:-
First, it has been found that, owing to glass being a bad conductor of; heat,.
the upper strata in the cistern, average, two, thousand five; hundred degrees
Fahrenheit, of heat, more than at the bottom. Now as, the salt,. potass, on
soda used in the manufacture of glass, is, evaporable, it is evident. that, from the
increased heat at, the surface,, the composition of the metal at the top must, be,
very different from that at the bottom of the cistern. Owing to the great.
loss, of salt,, the, refractive power of the glass also undergoes; a change, and;
its, rate of expansion and contraction, at, different temperatures. is in like
manner liable to be affected, which the increased: fluidity of the upper strata
adds to the general inequality of the mass. When, such a cistern, of, metal is,
thrown, out on the "casting table," and is rolled into a sheet,, the different,
portions of the metal, with their varied properties, come in, contact with each
other,, and where the more refractive portion joins, the, less; refractive,. the.
defect so, commonly occurring: (which is called; in, the trade; "waviness."
"wreaths"), manifests itself. Its liability to fracture, is: also much.
increased, from the, different compositions of the various: parts: in contact, or
rather in, union with each other, possessing different rates; of expansion; and:
contraction:
or
Secondly, another defect of the present system, arises; from: the heat; being:
principally applied to the upper surface of the glass in the cistern, whereby the
upper stratum of glass becomes hotter, and specifically lighter, than the under

page_text: one, which prevents a circulation of the particles forming the mass, the cooler
and heavier, strata ibeneath,being. stationary, by which means the desired, equal
mixture of the ingredients is greatly obstructed... The ascent and escape of
the thousands of air bubbles, or seeds" (as they are technically called) is.
thereby prevented, since their floating power is too small to allow of their
escape:
Thirdly, on the old system, in order to apply the reverberatory heat to the
best advantage, the mouth of the cistern, is left uncovered. This allows dust
to fall in, admits sometimes the smoke, which produces discoloration of the
metal. wherever it. touches; it admits sometimes small fragments off, the
angles of the bricks. or stones forming the arch, and what are called "tears'
to drop from the arch into it, these "tears" being formed by the action of the
evaporated salt acting on the fire brick or stone arch, and making a semi-
transparent glass, which; falling into the cistern, produces serious evils.
"
Fourthly, the difficulty of., removing one cistern in the old furnace without
cooling, the remainder, thereby creating much hurry and confusion in the
casting, from the necessity of taking so. little time to empty all the cisterns,
while, it often occurs that the glass in the cistern last drawn is not in. a
state to be used, or at any rate is much deteriorated in quality.
And lastly, the old system of heating is, most destructive to furnaces,.as.
their roofs or arches have to receive the heat to be given out to the cisterns.
And when these furnaces are once lighted they cannot be let out again without
destroying the arches, and the consequence is that they only last a short time,
in some cases only about fifteen months.
Before proceeding to describe the nature of our second improvement we
shall briefly describe how we propose removing. the, defects of the present
system in the particulars just described,.confining, ourselves .to. the "refining"
process; as a like arrangement may obviously be applied to, the "founding."
First, as the refractory clay of which, the cisterns are formed offers a great
obstruction to the passage of heat, we insert one..or; more plates..or, discs.of.
platinum in the bottom of the cistern, and so place the said.cistern in the fur-
nace as that its bottom is exposed to the direct action of the fire, the heated air
and flame, after striking the platinuni disc, making its exit through the openings
under the cistern into the upper annular space, where it encloses this cistern in a
cylinder of flame, meeting over its top in a cone, and then escaping, into the
flue. Our object in surrounding the cistern with flame is more for...the
prevention of radiation from the cistern than for the, transmission of heat to
the metal. The effect of applying heat through a thin plate of platinum at
the bottom will be to expand those particles of glass which first receive it, and

page_text: by their expansion to lessen their specific gravity, and to cause their ascent,
while the cooler and heavier particles will descend from the surface. This.
most important circulation of the particles is owing entirely to the application
of heat from below through the platinum disc; a perfect mixture of materials
will be the result. An almost perfect uniformity of heat, fluidity, and.
composition of matter will be thus produced, and in far less time and with less
consumption of fuel than by the old plan. A plate formed of such metal
would have no false refraction or wreaths, and would be less liable to fracture,
owing to the equality of its different parts. A still more important result is
obtained by this. constant motion of particles, namely, that thousands of
"seeds" or air bubbles, too small to extricate themselves from a mass of
metal in a quiescent state, will easily ascend to the surface in a fluid whose
particles are in constant motion. By heating from below we may place a lid
on the top of the cistern, whereby the dust and smoke are prevented from
falling into it; also any fragments off the arch and "tears" are effectually
excluded. The destruction of the furnace cannot be so great as on the old
principle, where the arch has first to receive the heat; but should it be preferred
to leave the cistern uncovered, there is no possibility of the angles of the
bricks falling into it, as we cover the furnace, as shewn in the Drawings
hereafter referred to, with a cone of fire clay in one piece, larger in diameter
than the cistern, and forming the upper part of the furnace, the inside to be:
glazed. to facilitate the running down on its surface of any "tears" that may
be formed. Our system of heating from below also has the advantage of.
considerable saving of fuel and time, as heat is so easily transmitted through'
platinum compared with fire clay.
The second important feature of our Invention is, the arrangement of the
furnace by placing each cistern in a separate chamber, whereby each cistern
may be removed for casting when ready without lowering the temperture of.
the rest. In the present furnaces five minutes are allowed for each of the six
cisterns (that being the usual number employed) being cast, and if longer
time were taken the last would be too cold, and if left to get up the heat.
again the glass would be spoiled by the undue evaporation of the salt.
Should it be found that all the air bubbles do not ascend, the process of
extracting the air bubbles from the melted mass by producing a vacuum upon
the surface, or greatly removing the atmospheric pressure therefrom, as also
shewn and referred to in the Drawings, will be found of great advantage.
When the cistern is removed from the furnace previous to turning out the
metal an operation called "skimming" is resorted to as a means of removing
the various impurities on the surface of the metal, for which purpose a

page_text: up
number of men surround the cistern with a long-handled skimmer, and take
the glass in small portions, and turn it over the edge of the cistern. The
evils of this system are, that as a thorough skimming would take too long, they
cannot see how much they have done from the intense light and heat affecting
the eyes, and the certainty of introducing air bubbles into the mass where the
metal falls back again that hangs to the skimmer. Our means of obviating
this will be seen in the Drawings annexed, and forms the third feature of our
Invention.
Our next improvement relates to the annealing oven used in the manufac-
ture of plate glass, and consists in forming at the bottom of the oven a flat
surface sufficiently large for annealing one plate. The oven may contain
many such surfaces. Each surface will be composed of a number of blocks or
hollow cubes of fire brick or other suitable material, first subjected to a heat
at least four times greater than they will afterwards have to undergo. When
cold they are fastened or connected together by bolts and nuts, or other means
(their sides being ground to fit close), hollow cubes being preferred for this
purpose, as affording facilities for bolting together, and giving the required
strength with a small weight of materials. These annealing tables or surfaces,
composed of blocks as aforesaid, will be ground to a perfect level by the grinding
apparatus now used for grinding plate glass. Upon these tables or surfaces
the plates of plastic glass just formed will undergo the annealing process and
be allowed to cool, solidifying in contact with the level surface, and thereby
becoming equally level. By this means a great saving will be effected, not
only in the time occupied in grinding, but also in the material itself, as, owing
to the very uneven surface of the present oven, the plate of glass is often so
very much out of the level, and the surface so indented, that more than one
half of the glass is ground away before it is in a fit state for sale, and as the
duty is paid upon it in the state in which it is brought out of the annealing
oven the loss is very great.
Our last improvement relates to that description of glass called flint glass,
for optical purposes, and consists in an apparatus by which the fluid metal in
the pot is prevented from depositing its heavier particles, and producing layers
or strata of various density, as is the case at present. These evils we prevent
by causing the pot to revolve, and closing the mouth of it, so that there shall
be no space vacant within it, thus excluding the air, and keeping the glass of
an uniform consistency.
And in further compliance with the said previso, we, the said Henry
Bessemer and Charles Louis Schönberg, do hereby describe the manner in
which our said Invention is performed, by the following description thereof,

page_text: DESCRIPTION OF THE DRAWINGS.
Sheet 1. Figure 1 is an elevation of our improved furnace; Figure 2 is a
vertical section of the same, and Figure 3 is a horizontal section or plan taken on
the line A, B, through the upper openings where the melting cisterns are intro-
duced. And we would here observe that we have used similar letters to denote
similar parts in all the Figures. A, A, is the masonry of which the furnace is
composed, being built of fire stone of the usual description. B is the main
flue or chimney. C, C, C, C, C, C, six openings or compartments, each forming
distinct furnaces, with fireplaces D to each, and ash pits E under the same;
the interior of the furnaces C are lined with the brick, and at top of each is a
conical cover F, composed of the same material. These coverings have holes
at top communicating with the small flues G, which lead to the main chimney
B. The flues G are each provided with dampers.
The peculiar form of the top F of the furnaces C is an essential feature of
our Invention, and we shall hereafter explain the advantages which will
arise from its use in the melting furnace. H, H, is a circular piece of fire clay
which is moulded to fit the ledge I between the furnace C and fireplace D, and
upon which it rests, forming a stand upon which the melting pots are placed
whilst in the furnace, see Figure 4, where we have shewn these stands on an
enlarged scale. There are openings h which allow the flame and' heat from the
fireplace to pass through and circulate round the melting pot. J, J, are doors
composed of fire brick, and strongly clamped together with iron bands, which
close the furnaces during the process of melting; K is the refining cistern
melting pot, made of the usual material and of the usual form; but the bottom
L is composed of platinum, and made moveable to allow of its being removed
as occasion may require, to other cisterns; this is shewn on an enlarged scale
in Figure 5, and we have also shewn other forms of melting pots in Figures
6 and 7, the latter being exactly like that shewn in Figure 5, excepting that
the bottom is made of the same material, but thinner than the other part of
the pot. M, M, are the handles by which the pot is removed from the furnace.
The pot shewn in Figure 6 is of a different form to those last described, having
a dome-shaped bottom, and in addition to the handles a projecting band N is
formed all around the outer surface, upon which it rests during the process of
melting; and when this form of pot is used an alteration must be made in
that part of the furnace where the stands I rest, as previously described; for
instead of the ledges upon which they are placed the top of the fireplace is formed

page_text: with 'openings:O, O, as shewn in Figure 8; and the band N of the pot will rest
upon the intermediate'spaces between the openings, leaving sufficient room for
the flame and leat to circulaté round the pot. In order more perfectly to
skin without admitting air bubbles into the mass of the melted glass, we place
barred rings P; P; on the top of the pots, keeping the level of the glass above
the junction of the ring with the pot, and by passing a metal plate Q-between
the rings and the pot, as shewn in Figure 9, the ring and the scum within it
will remain on the top of the plate, and be removed from the pot. This is
more clearly seen in Figure 10, where it is shewn on an enlarged scale. In
the process of manufacturing plate glass as at present practised, it is well
known that an evaporation takes place during the process of melting, and from
the usual construction of the furnace and position of the melted pots placed
therein; the condensation which takes place on the dome of the furnace causes
what are technically called "tears" to drop into the melted glass and produce
the most injurious effects. To obviate this we have given to the cover F of
our improved furnaces a conical form, and we also glaze the inner surface of
this cover, so that any fluid which may form upon it will run' down to the
base of the cone and drop outside the melting pot.
:
Having now described our improvements connected with the refining
process, we will proceed to describe a process for extracting any minute air
bubbles from the melted glass that may not have escaped during the refining
process, and for this purpose we must refer to Figure 11 in Sheet II of the
Drawings. As soon as the melted glass is removed from one of the furnaces
C; the cistern is placed within à metal cylinder S, which is lined with fire
brick' to prevent the escape of heat as much as possible, the bottom of the
lining being ribbed or grooved so as to form a communication with the
opening T in the centre; the top edge of the cylinder S must be accurately
ground and fitted to the bottom of the cylindrical cover U, which is suspended
over it, and as soon as the melting cistern is placed in the cylinder S the cover
Umust be lowered on to it. Y. is an 'air pump,' which is kept in action by a
steam engine or any other power; this pump communicates with three cylin
drical vessels W, WW, by the pipe V; which form vacuum chambers.
To these chambers pipes Z Z2, Z3, are attached, which are connected to the
valve box a, and which in Figure 11 are shewn closed by the slide 6: This
slide is provided with a spring, and has an opening c in the centre, to form;
when moved over the openings of the pipes Z (by turning the handlese) à
communication between the valve box and the vacuum chambers; but when
placed in the position as shewn in Figure-11 a communication is formed
between the valve box and the atmosphere which will allow the air to flow
M

page_text: into the cylinder S by means of the pipe d and the cover U to be lifted up.
'e is the handle, the spindle of which is screwed and works in a box f, and by
this means the valve is moved backwards and forwards. The object of this
apparatus is to extract any air or air bubbles that may be left in the melted
glass after being removed from the refining furnace previous to its formation
into a plate. And it will be evident that if a vacuum is maintained in the
chambers or vessels W', W, W³, that the air contained in the cylinder S and
cover U will rush into the vessel W¹ by the pipe Z, whereby its density will
be lessened in proportion as the vessel W₁ is larger than the vacant space in
the cylinder S and cover U. The further rotation of the handle e will bring the
slide 6 over the second pipe Z, closing the communication between the cylinder
S and vessel W₁, and establishing a communication with the vessel W2 and
cylinder S; the small remaining portion of air left in the cylinder S will again
divide itself equally into the increased space thus formed; the still further
progress of the handle e will bring the slide b over the opening of the last pipe
Z³, and close the communication with the chamber W, whereby the minute
portion of air left in the cylinder S and cover U will again expand itself into
the increased space thus formed between it and the chamber W³, and by this
arrangement of having chambers ready exhausted an almost perfect vacuum is.
formed in much less space of time than if the operation had to be performed
by the air pump in direct communication with the cylinder after the cistern
had been placed in the cylinder. The atmospheric pressure being thus
removed from the surface of the melted glass, the globules of air contained
therein will become greatly expanded, and thereby acquire sufficient floating
power to rise to the surface, and this operation requiring only about two
minutes the glass suffers scarcely any loss of heat, and is now in a perfect
state for casting. We will here observe that Figure 12 is a plan of
Figure 11, and the various parts are referred to by similar letters in both
Figures.
Our next improvement relates to the bed of the annealing oven, which we
construct of square blocks, as represented in Figures 13, 14, 15, 16. These
blocks are hollow and open at bottom, as shewn in Figures 15 & 16; they
may
be made of any size to suit the form of the oven, as may be most con-
venient, but we prefer them to be about two feet square. The sides are to be
ground and fitted to each other, and connected together by screws and nuts
(or any other method), grooves being formed in the sides of each block, into
which clay or cement is forced to prevent their shifting, as shewn at t in
Figures 14 and 16. As soon as the whole is fitted together it will form a
surface on its upper side, as shewn in Figure 13; and previous to its being

page_text: placed in the oven we place it in the ordinary grinding machine, and make it
as level as possible, when it is set in sand in the ordinary way. In some cases.
it may be desirable to have moveable bottoms to the annealing ovens, and for
that purpose we have provided rollers k, k, as shewn in Figures 17, 18, & 19,
and upon which it can be moved in or out as occasion may require. This.
table or platform varies in this particular from that last described, we do not,
therefore, consider any further explanation necessary.
We will now describe the apparatus for cooling down the pot of melted
glass, which is applicable to that description called flint glass, for optical
purposes. It is shewn in Sheet II. at Figures 20 and 21, and consists of two
upright standards 1, 1, forming bearings for the spindle m, which spindle has a.
ring in the centre at o, and a band pulley n fixed thereon, by which it is made
to revolve. The pot of melted metal p is placed by hand in the ring o, and the
protecting pieces on the pot rest upon it; the cover a must then be screwed
down upon the pot by the screw r, and the spindle being placed within the
bearings of the standards I, 1, the pulley may be put in motion by a steam
engine or any other motive power, and thus kept revolving until the glass is
cooled. By this means the particles of glass are kept in equilibrium, and no
deposit can take place of the heavier particles, as is the case at present,
whereby the glass will become more uniform in its mixture and free from
"striæ or wreaths," which is now so commonly found in that made upon the
present system.
Now whereas we claim as our Invention,-
First, forming our furnaces in such manner of solid masonry in the centre,
and with separate chambers and fireplaces arranged round that solid centre, so.
that each cistern or pot may be heated independently of its neighbouring.
cistern or pot, and withdrawn from the furnace to be emptied of its contents
when the glass contained therein is in a fit state for being operated upon
without affecting the temperature of the other pots or cisterns in the furnace,
as shewn in Figures 1, 2, and 3, as also the conical-shaped covers placed over
each separate furnace, and which we prefer to be glazed, to prevent the falling
of tears into the melted glass.
Secondly, the introduction of a platinum moveable bottom to the cistern or
pot, and the application of a top ring thereto, as shewn at Figure 5. Also
the application of a thin moveable clay bottom and top ring of clay, as shewn
at Figure 7, and the indented or perforated rings on which these cisterns or
pots rest, as shewn at Figure 4.
Thirdly, the cistern or pot with a thin fixed bottom of the form shewn in
Figure 6 and top ring also, as before described, this cistern being supported
on the ring, as shewn at Figure 8.

page_text: Fourthly, the mode of skimming by means of the top ring and hanille,
cutting plate.shewn at Figure 10.
Fifthly, placing the cistern or pot in a vacuum in order to exhaust the air
from the glass contained therein previous to its being poured upon the table,
as shewn at Figures 11 and 12.
Sixthly, an annealing table, the various parts of which we prefer to be of
fire brick, but which may be made of stone of any suitable kind to stand great
heat, united together to form one solid mass, and ground or otherwise brought
to a perfectly level surface, as shewn in Figures 13, 14, 15, and 16.
And, lastly, causing the glass used for optical purposes to revolve during the
process of solidifying, as shewn at Figures 20 & 21.
In witness whereof, we, the said Henry Bessemer and Charles, Louis
Schönberg, have hereunto set our hands and seals, this Twenty-third
day of March, in the year of our Lord One thousand eight hundred
and forty-two.
1
HENRY (L.s.) BESSEMER.
CHAS LOUIS (L.S.) SCHÖNBERG.
AND BE IT REMEMBERED, that on the Twenty-third day of March, in
the fifth year of the reign of Her Majesty Queen Victoria, the said Henry
Bessemer and Charles Louis Schönberg came before our said Lady the Queen
in Her Chancery, and acknowledged the Instrument aforesaid, and. all and
every thing therein contained and spcified; in form above written. And
also the Instrument aforesaid was stamped according to the tenor of the
Statute made in the fifty-fifth year of the reign of His late Majesty King
George the Third.
Inrolled the Twenty-third day of March, in the year of our Lord One
thousand eight hundred and forty-two.