GLASS-MAKING.

5S1

0 parts of quartzose sand require 33 parts of dry carbonate of soda for their vitrifica-a, and 45 parts of dry carbonate of potash. Buf to make unchangeable alkaline glass,P ec ‘ally with potash, a smaller quantity of this than the above should be used, with a'T vudent heat. A small proportion of lime increases the density, hardness, and lustrein ’ an I it aids in decomposing the alkaline sulphates and muriates always presentfor in P ear iash of commerce. From 7 to 20 parts of dry slaked lime have been addedth 1 t °*' s ^* ea > with advantge, it is said, in some German glass manufactories, wherec artli a '* ne ma ^ er * s sol ^ a > f° r potash does not assimilate well with the calcareous

hiaf 1 * Inail 5' glass works on the Continent, sulphate of soda is the form under which alkalineco l r ' s introduced into glass. This salt requires the addition of 8 per cent, of char-°nt L° ^ ecom P ose and dissipate its acid; a result which takes place at a high heat, with-and n addition of any lime. 88 pounds of quartz-sand, 44 pounds of dry glauber salt,a Pounds of charcoal, properly mixed and fused, afford a limpid, fluent, and workablepi ss .i with the addition of 17 pounds of lime, these materials fuse more readily into ain® f mass- df less carbon be added, the fusion becomes more tedious. The two foliow-6 *°rtnulee afford good glauber salt glass.

I.

2.

Sand

100

60-3

Calcined sulphate of soda

50

26-8

Lime -

20

10-8

Charcoal -

- 2-65

2-1

“rst mixture has been proved in the looking-glass manufactory of Neuhaus near

^ite first t....., B ._..

j^ eaaa j and the second by the experiments of Kirn. The fusion of the first requiresWlp t *' e secon d 21 hours. The bluish green tinge which these otherwise beautiful andar's Iarit glasses possess, is not removeable by the ordinary means, such as manganese orin e 1 ' 1 '’ decolor alkaline glass. When the sulphate of soda and charcoal are used

t0 *aller proportions, the glass becomes more colorless. The tinge is no doubt owingWu e su lpfiur combining with the oxyde of sodium, in some such way as in the pigmentdrive.

Sjp/ a Proper addition of galena (the native sulphuret of lead), to glauber salt and quartzs ulnh ' v f^ out charcoal, it is said a tolerably good crystal glass may be formed. Thei n th Ur ‘ c ac *fi of the salt is probably converted by the reaction of the sulphuret of leadq su ‘Phurous acid gas, which is disengaged.

of a, °m of sulphuret of lead = 1495-67, is requisite to decompose 3 atoms of sulphatetajp Jp = 2676. It is stated, on good authority, that a good colorless glass may be ob-a by using glauber salt without charcoal, as by the following formula.

The melting

100 pounds242012

A small quantity of the sand is

Quartz-sand -Calcined glauber saltLime -

Cullet of soda glass

fe Ser " \ ueiwn S heat must be continued for 26| hours. __ u ..j _-

. to be thrown in towards the conclusion of the process, in order to facilitate theof ^ Sl0a a ^ r bubbles. The above mixture will bear to be blanched by the additionn ? atl ese and arsenic. The decomposition of the salt is in this case effected by thea hd. w hich the sulphuric acid first combines, is then converted into sulphurous acid,sili c 1Ss *P a ted. Glass made in this way was found by analysis to consist of 79 parts ofqu bine, and 9*6 soda, without any trace of gypsum or sulphuric acid,of tbg er sa lt is partially volatilized by the heat of the furnace, and acts upon the archthe 0 ot° V€ft ant ^ t°Ps tl le pots. This is best prevented by introducing at first intothe Sa w bole of the salt mixed with the charcoal, the lime, ami one fourth part ofrem ai( 5 l ’ ** us ' n £ this mixture at a moderate heat, and adding gradually afterwards theXv ho] e ■ ei * sand, increasing the temperature at the same time. If we put in th*e

the bott redie ” ts to " ether > as is done with potash glass, the sand and lime soon fall toUn eq Ua i° ms w b*l e the salt rises to the surface, and the combination becomes difficult and

b otas b act s in the same way as sulphate of soda.

1*he jh 0 . e SOt ^ a a l so > according to Kirn, may be used as a glass flux with advantage.*§reeablv t SUl !^ble proportions are 4 parts of potash, 2 of common salt, and 3 of lime,y to the following compositions :—

Quartz-sand _

Calcined carbonate of potashCommon salt .

Lime «...

I.

2.

60-0

75-1

17-8

19-1

8-9

9-5

13-3

14-3