CHEMISTRY,
THEORETICAL, PRACTICAL, AND ANALYTICAL,
AS APPLIED TO THE
ARTS AND MANUFACTURES.
GLASS . —The transparent compound distinguishedby this name is produced by the fusion of silicicsalts of the alkaline and earth metals. The etymo-logy of the word has been much disputed. It isderived by some from the Latin glades, ice, itsresemblance to which is thought to have suggestedthe title; and glades may be a contraction for gelades,from gelu, frost. Others have remarked that thecommon Latin designation of this substance is vitrum;and as the Romans applied this term, in commonwith the word glastum, to the plant which is nowcalled woad, they have deduced it from the latterof these, either because the ashes of this plant wereused in the manufacture of glass, or because itexhibited something of the bluish tinge which isprocured from woad. Glassum, the name given toamber by the ancient Gauls and Britons, has alsobeen assigned as the origin of the word. But noneof these etymons appears very satisfactory. Theuiost plausible theory is that which derives the termfrom the Saxon verb glis-nian, or the German gleissen,which are probably contractions of the Anglo-Saxon gel-ixan, to shine, to be bright. This view is in agreat degree confirmed by the sense in which theterm glass and its derivatives are employed by ourolder writers, who frequently apply it to shining orglittering substances, without reference to colour°r transparency.
Glass is a mixture of potassium or sodium silicate,°r of both, with one or more silicates insoluble inWater—such as the silicates of barium, strontium,oaleium, magnesium, aluminium, manganese, iron, orlead. Potassium or sodium silicate (water glass),°r a mixture of the two, even with a sufficientquantity of silica to form a very infusible glass,' v ould still be affected by water and acids. Calcium
VOL. II.
silicate is likewise acted on by acids, but a mixtureof it with sodium or potassium silicate resists theiraction.
Such mixtures of silicate of soda or potash withsilicate of lime, &c., are more fusible than the simplesalts, and require a smaller amount of silica torender them capable of resisting the action of waterand of acids. They contain between 2 and 3 atomsof silica to 1 atom of the metal, and still less whenalumina is also present.
The larger the proportion of silica and alumina aglass contains, the more infusible does it become,and the greater resistance does it offer to the actionof acids and alkalies. But the greater the excess ofpotassium, sodium, barium, calcium, magnesium, orlead which it contains, the more easily is it fusedand attacked by water, acids, and alkalies. Accord-ing to Baudrimont and Pelouze, the lustre andrefractive power of glass increase with the atomicweight of the metals contained in it; thus thesequalities are possessed in the highest degree by leadglass, next by baryta glass, next by potash glass, andleast of all by soda glass (Gmelin, vol. iii.).
In the most remote ages the art of blowing glassinto bottles, making it into vases, tinging it toimitate precious stones, melting it in huge massesto make pillars, rolling and polishing it into mirrors,and staining it in parts, were all perfectly known.In all probability Egypt , the parent of so manycollateral arts, is to be looked to as its source.
If Pliny is to be credited—an author whoseversion of the subject has so often been reproducedwith all the gravity of history—the discovery ofglass was made by some Phoenician soda merchants,who, having landed on the banks of the river Belus,served themselves with blocks of soda to supportthe vessel in which they prepared their food, and1