of borax. To these are sometimes added a smail quan- 
of lime and , according to circumstances. 
sand and i, and also the lime and manga- 
nese, if any are used, are first well mixed together, and 
thrown into a reverberatory furnace, represented in 
section by Fig. 11, where A is the fire-place, situ- 
ated between two circular ovens or domes B, upon the 
flat floors ates the Palbagres ao laid ; and the 
flame risi e grate being reflected down by the 
diched veil strikes upon the floors of the ovens with 
sufficient heat to nearly fuse the materials, and cause 
the sand to become very white by a semi-vitrification. 
This calcination is continued for five or six hours, and 
the materials are constantly stirred and — over with 
an iron poker, to expose every to heat, until 
they cea to ford oy vapotr, or t undergo ay ar 
A plan of the furnaces used by the French is given 
-at Fig. 12. of Plate CCLXXVI. and a vertical section 
‘at Fig. 13, the same letters being used in both. The 
real ce A, which contains the two large pots a, a, 
‘and two others on the opposite side, is surrounded by 
. four other furnaces or ovens B, B, B, D, which proceed 
from the angles, and are heated by the flame of the 
same fire passing through flues g,g. The three ovens 
‘marked B, B, B are intended for burning the pots in 
which the glass is melted and refined, and also tue cis- 
‘terns into which itis put, to be conveyed to the casting 
tables. The fourth oven D is intended for heating the 
frit or material, previous to its being put into the pots 
‘to be melted down. The four ovens are all of the same 
form and dimensions, except that the openings 5, 6, in« 
to the three first are larger than the mouth d of the lat- 
ter: all these oe are closed by doors of bricks 
fitted in iron frames. The fire is made in the bottom of 
the great furnace atE, Fig. 13, being included between 
two sloping walls e, e; which form the benches or seats 
for the four 3 two pots a, a being placed upon each 
bench, and likewise two cisterns m, m, which are 
at the ends of each bench; and therefore, in the four 
angles of the furnace, the form of the arched roof FF 
is —— to nthe the oo down into and 
upon , to which it gives the greatest heat, and 
Bon paneot by the flues g, g, 9,2, Fig. 12. into the 
four ovens B, B, B, D. Thefuel is supplied through arches 
E at the end of the fire-place, which are of sufficient 
size to introduce a new when ; but when 
the furnace is at work, t arches are bricked up, ex- 
cept a small opening at the bottom. On each side of 
the furnace are three working holes i,/, h, to admit la- 
dles, by which the glass is put into the pots a, or taken 
out ‘ind transferred to the cisterns m; and, in order to 
‘withdraw the cistern from the fire, a door or opening 
is made in the wall before each, as shewn at ]/, Fig. 12. ; 
j and the dotted lines represent a flooring of iron plate at 
the level of the bench, upon which the cisterns are re- 
ceived when drawn out of the furnace, which is done 
a large pair of forceps, Fig. 14. mounted upon 
wheels. 
The are placed inthe ovens B. The flues which 
admit the fire into them, are provided with dampers, or 
sliding doors, which are closed until the pots are placed 
in the oven. The dampers are then opened very little 
at first, to admit the heat gradually, and avoid the dan- 
rie cracking the pots. The cisterns are made and 
ed in the same manner. 
The frit is mixed with the ts of old glass, 
es tetee opera, by heating them in the 
oven D to redness, and throwing them into cold water. 
VOL. X, PART 1. 
GLASS. 
313 
To this mixture of frit and glass is added the fluxes of Plate Glas. 
nitre or borax, and the composition is baked for some ““Y"” 
hours in the oven D, util, by the commencement of the 
vitrification, the materials are reduced to a sort of thick 
. This istaken out of the oven in long ladles, car- 
ried to the mouth 7 of the furnace, and put into the great 
_ a,a, which are already heated. Here the t 
eat vitrifies, and changes the frit into glass. It re~ 
uires a fusion of 36 or 48 hours to make fine «1d 
clear glass, and sometimes more, If it is found thick 
or opal like porcelain, the heat must be continued for 
a longer time, or a greater proportion of flux must be 
added ; borax is the best for this additional flux. If it is 
found to be a perfect substance of glass, but coloured, 
ae or the — of — is put in. = this 
‘ are tied up in a thi at the end of 
secdites onl, guid put rh to the Seton of the 
A mixture of arsenic and ma is used at other 
times, according to the nature of the coldur, which is 
intended to be corrected. 
When the glass is completely vitrified, it is taken out 
of the pots in ladles, and poured into the cisterns which 
stand at the sides of the pots. The cisterns must be in- 
troduced into the furnace whilst they are hot, both to 
save Aime in heating them in the great furnace, and al- 
so to avoid the of cracking them by a sudden 
exposure to so great a heat. For this purpose, a cistern 
is taken from oven B, in which it was baked, 
drawing it with hooks to the mouth or door; and it is 
then seized by the tongs, Fig. 14, which area very lar, 
pair of pincers, united by a joint pin a, fixed into the 
axletree of a pair of wheels 6, upon which the whole 
runs. The beaks or jaws d, d, are properly adapted to 
receive the cistern between them ; and, for this purpose, 
the cistern has a ein each side. The opposite 
ends of the tongs have handles e, e, by which the men 
guide and direct the machine ; and also a smallarch g, 
with pin holes to make fast the ec when they have 
seized the cistern. Having taken hold of thefcistern with 
this machine, by two men weighing on the handles e, ¢, 
they can readily take up the cistern off the floor of the 
oven, and by the wheels transport it to the furnace, 
into which they introduce it through the lower open« 
pe sah If it is a cistern which has been used before, they 
e the opportunity of its being hot to clean out the 
old shes its sides. The glass remains five or six 
hours in the cistern until the whole is brought toa white 
Fusion, 
Fig. 14, 
heat. The door at /, Fig. 12, ite the cistern, is 
then removed, and the cistern wit! wn by the pincers, 
aided by long iron hooks, Being then carried to the 
casting table, represented in Fig. 15, it is taken up b 
rapes and its contents pound out upon the ible, 
upon which it spreads into a thin sheet. 
The table AA is strongly framed in wood, and co= Castiag 
vered over with a thick plate of copper, made very table. 
smooth upon: the surface. B is a heavy cylindrical rele P1ATE 
ler of copper, which is used to roll over the fluid glass, ©C'X*V"- 
and flatten it to the required thickness. To regulate Fis 1° 
this thickness, two iron rulers a, a are laid down u 
the table, at such a distance as will inelude the width , 
of the intended plate ; and the thickness of the rulers 
is equal to that of the plate, because they bear up the 
erp eS 
ro projecting spindles at end for 
two men to roll it along by; and that it may advance 
steadily, they are counteracted by two other men, who 
hold rods c, c, and re the advance of the roller. 
The cistern D is up in apair of tongs E, shewn 
separately in Fig. 16, They open and shut upon the 
‘ 2R 
