June 1, 1864.] THE TECHNOLOGIST. 



ON GRANITE AND ITS USES. 501 



curved and waving outline, and, though sharp enough to hurt, are 

 blunted on their edges. This waving, sinuous line is closely related to 

 a property of glass, which connects it with the most glass-like of the 

 amorphous bodies — viz., the jellies. If we take animal jelly or gelatine — 

 for example, thick liquid isinglass or glue — we can draw it out into 

 threads, and mould it into pliant shapes. But it is too semi-liquid in 

 character, too unsolid, to admit of being condensed into permanent 

 forms. Glass, however, at a certain stage in its passage from the per- 

 fectly liquid to the perfectly solid form, has this jelly-like or viscous 

 plasticity, so that it may be run into moulds, spun into gossamer threads, 

 blown into bubbles, drawn into tubes, rolled out and stamped as if it 

 were dough, clipped with scissors, pared with knives, squeezed, twisted, 

 compressed, dilated, pulled out, pushed in, patched, puckered, smoothed, 

 and welded, as if it were a ball of softened India-rubber or steam-hot 

 gutta percha ; whilst, in addition, glass finally settles or consolidates 

 into a mass of stone-like hardness, which may be broken but will not 

 bend. 



Glass, then, has the following characters: — 1. A brilliant lustre, 

 which in other bodies we call the glassy lustre ; 2. A shell-like or con- 

 choidal, curved fracture ; 3. A jelly-like plasticity, when passing from 

 its liquid to its solid condition. Its particles are not marshalled together 

 in the same rigidly harmonious way that the particles of crystals are, 

 neither are they grouped or piled on one another, in the irregular fashion 

 which characterises coagulated or amorphous masses ; but it is impos- 

 sible to give a precise definition of the internal structure of glass. In 

 our ordinary language we restrict the word " glass " to a very few silicious 

 compounds, but this is a merely conventional restriction. Thus, the 

 simple combustibles, phosphorus, sulphur, and carbon (as the diamond), 

 can put on all the characters of glass. Many acids and their salts, such 

 as phosphoric, boracic, and silicic acid, do the same. So do metallic 

 oxides, such as oxide of lead, and many vegetable products, such as 

 the gums, resins, and sugars. 



All bodies possessing the characters named above constitute glass, 

 whatever their nature or composition may be ; and as the glassy or 

 vitreous state and structure are intermediate between the amorphous 

 and the crystalline one, so all kinds of glass are liable, on the one 

 hand, to degenerate, as it were, into shapeless amorphism, or, on the 

 other, to develop into symmetrical crystallinity. For example, the bril- 

 liantly combustible phosphorus, which we believe to be a simple or 

 elementary substance, exhibits in its ordinary form, as melted and pre- 

 served under water, the glassy structure. But if we keep it long melted 

 at a comparatively low heat, it becomes a crystalline mass, showing 

 sometimes perfect twelve-sided lozenge-faced crystals (rhombic dode- 

 cahedrons), like those of garnet. Again, if we keep it long heated, at a 

 comparatively high temperature, it ceases to be either vitreous or crys- 

 talline, and becomes totally amorphous. 



