Flint Glass. of which there isa plate of iron fastened "to prevent . 
—_—— 
Method of 
making 
wine 
glasses, 
Flint glass 
for optical 
purposes. 
312 
the burning of the chair by the hot iron pipe and glass ; 
for the operation must be-done with the greatest quick- 
ness while the metal is hot. He rests the pipe across 
the chair arms, and, while he rolls it back forward 
with his left hand, he with an instrument similar to a 
small pair of tongs, catches the.solid metal at the end 
of the hollow ball and draws it out, at the same time 
giving it the shape required for the stalk of a wine 
glass; another blower is: going on with the same pro- 
cess, and blowing a smaller ball ; and_after giving it a 
sharp cut at the end of the blowpipe, he quickly presses 
it against the point of the stalk of the glass in the other 
man’s hand, to which it readily adheres as firmly as if - 
there had never been a joint; and, by giving ‘the pipe 
a smart stroke with a small piece of iron, it is separated - 
from the small ball now attached to the ‘stalk of the 
glass, which is instantly given to the finisher or work- « 
man, the others being called blowers or footmakers. 
This workman then makes the glass just hot enough 
to keep it from breaking, and sits down on his chair, 
‘and with a similar pair of tools, while rolling the 
pipe rapidly on the arms of the chair, he opens the 
ball at the stalk of the glass, and forms a foot. A 
boy then takes a small rod of iron, called a Ponty, and 
dips it into the metal in thepot, takes out on the ex- 
tremity of the red.a small portion of glass, thrusts it 
immediately against the centre of the foot, to which it 
instantly unites. The workman then with a piece of 
iron, which he wets with his mouth, touches the globe 
‘intended for the bow] of the glass with the wet part, 
-which is still very hot, although so much chilled as to 
retain its shape, and this in a second or two cracks it . 
round ; and, by giving the pipe a gentle knock, it se. 
parates from it, and leaves an o uneven mouth, 
~which the workman instantly heats, and with a pair of 
shears, clips the heated glass smooth and even im’ ‘the 
mouth; but as the shears have put the glass off ‘that 
‘circular form, he heats. it again, “and: by a dexterous 
twirl and swing round-his head, he, if an expert work- 
man, gives it the desired shape to a mathematical ex- 
actnes, almost without the aid of any tools. | The wine 
glass now finished and chilled a little, by giving the 
ponty a smart blow, the glass separates from ‘the iron, 
and is carried by a boy with a long forked iron to'the 
leer, or annealing furnace, where it is 
already heated for the purpose’ of enbenting. 
The following is the composition of the finest ‘flint 
glass: Fine white sand, 300 parts; red lead, or li- 
tharge, 200 ; refined pearl ashes, 80; nitre, 20; arsenic 
“and manganese, a small quantity. * 
These, all mixed together with the utmost nicety, are 
termed a flint batch. 
The following results were obtained by M. Zeiher 
of St Petersburgh, respecting the optical effects of va- 
rying the proportions of the ingredients of flint glass. 
Proportion of red lead to | Index of re- | Dispersion of the rays 
flint. fraction, | #2 comparison of crown 
glass, 
Red lead. Flin 
dese “3 1 2.028 | 4800 to 1000 
2 2 1 1.830 «| ' 8550 to 1000 
3 1 1 1.787 3259 to 1000 
4 2 1 1,732 ° 2207 to 1000 
5 | ; 2) | Lea ° | 1800 to-1000 
6% | 4 1 1.664 1354 to 1000 
4 
GLASS. 
laced in 'a pan - 
From this Tuble, it is obvious that a ; 
of lead'not only increases the refracti so’ th 
dispersive powers of the glass. W ‘Leib 
alkaline salts with his glass, he found that they din 
-nished the other refraction, without. 
in the dispersion. He-then obtained a kind of 
which had three times the dispersive power, of: er 
glass, and a refractive-power of only 1.61. . See r 
dead. Berl, 1766;-p.dG0i4 2 Rel Sie eae, oS 
- M. Cazalet of Bourdeaux, has lately announced ame- Ca 
-thod of making flint glass for telescopes free of all veins 
and imperfections. It consists of | Bb tithe 5 
PSs 
: SPP) dts? ae Re DS OR 
Red lead, pure and sifted through silk, 100 parts. » 
Nitre,, purified « jv2 + séyer shapettay slo came ene 
Very pure and whiteichalk (4 bshier kh 
Pure white sand . er > w6O~ asap 
ble of ried - 
ase furnace. After 36 hours, it will be 
melted, | 
-of 48 hours itis poured upon a warm of 
upon which. it is allowed to cool pinion pee 
4 west 
then be found free of all imperfections, § © 
A number of interesting s on-the 
facture of flint glass for opti has been mad 
by M. D’Artigues. He always found. that the excel- 
Jlence’of the int glass Sense ification. ; 
the red lead; that the middle part of a» mass of 
“glass was always the freest from veins ; that itis 
‘only good when it is manufactured on a eae 
-The middle portion of the pot of glass is 
»cylinders, and: afterwards into 
detin de la Societé d’ Encouragement, N° 83.00 
- 
4 ; - A Tee a 
“Seer. VIL On the Manufacture ‘of Plate Glass: 
nitre, or salt, and sometimes wine mets a 
rable qualities in plate glass are, that it shall be) 
ly branegnaent and colourless, free from bubbles 
specks in the casting. To attain this it mast melt w 3 
.a moderate degree of heat; . for, without this quality, 
it is scarcely le ones Frain ner. 4 
will not cool-in some degree during the operation, ‘and 
thus have specks. The best alkaline substance, for the 
flux is soda extracted from the ashes of barilla by lixivia- 
‘tion. If pearl ashes are used, they should ped aruba 
purities will subside ; and the ‘clear liquor which is — 
drawn off must be boiled down iniroe pied ee 
evaporation of the water, the clean ashes are d. 
Borax is very useful to facilitate the fusion, and also 
the running into ‘plates. Lime: has ‘the | x ] 
but the quantity must be small, otherwise it will af 
fect the transparency. i. iva I5 els Boe 
The composition recommended by the author of 
Handmaid to the Arts, is 60 parts o white sand rf 
clean, 25 parts of pearl ashes, 25 parts of nitre, and 
whodls Laut. bercary 
= 
