June 1, 18G-1] THE TECHNOLOGIST. 



ON GRANITE AND ITS USES. 497 



of lightning in reducing the most refractory minerals to the 

 condition of clear glass ; to the effect of great casual conflagrations in 

 reducing portions of buildings to vitreous masses ; and perhaps, most of 

 all, to the effect of the prolonged heat of furnaces, in causing the ashes of 

 the fuel burned in them to glaze the stones or bricks of their walls and 

 floors, and in fusing the calcined dross or scoriae of metallic ores into slag, 

 i.e., opaque glass. 



Such phenomena must more or less have awakened the interest and 

 attention of even rude workers, since fires were first lighted ; and in all 

 probability the ancient arts of the baker, potter, and blacksmith were 

 not long practised before the dwellers in widely distant regions of the 

 globe had learned the first principles of glass-making. It is thus, in all 

 likelihood, one of the oldest of the arts. It is, at all events, a very old 

 one, for we know, from drawings in the Egyptian tombs, and from 

 objects found in them, that 2,000 years B.C. expert glass-blowers 

 abounded in Egypt. 



The word "glass" is perhaps derived from the Latin word for ice, 

 "glacies," from which we derive our words " glacial " and "glacier," but 

 this is uncertain. The thing itself is very familiar to all of us, though pro- 

 bably most would be puzzled to define or describe it. Its only synonym 

 is crystal, and this teim may connect it with rock crystal or silica, which 

 is the largest constituent of all the ordinary kinds of glass. The most 

 remarkable thing, however, about glass is not its materials, but, as in 

 the precious stones, its workmanship ; and in the full sense of the word, 

 as understood by natural philosophers, glass signifies a solid body pos- 

 sessing a peculiar structure, not a peculiar composition. In other words, 

 it is the mode in which its particles are arranged together, not the nature 

 of its particles, which makes glass, glass. 



To render this clear, let it be observed that (setting aside plants and 

 animals, the forms and structures of which are foreign to our present 

 inquiry) three quite unlike external shapes and internal arrangements 

 of particles are found in solids. These three are not the only kinds of 

 form and structure found characterising dead matter, but they are the 

 three most striking which prevail in those solids which have not formed 

 parts of living beings. They are as follows : — 1. Some solids are crys- 

 talline in shape and structure ; 2. Some are glassy or vitreous ; 3. Some 

 are neither crystalline nor glassy, and are called amorphous, i.e., form- 

 less or shapeless, but the adjective also includes the idea of their being 

 structureless. Glass is intermediate in character, between a crystalline 

 substance and an amorphous one, and it is rather unfortunate that one 

 kind of glass should be called " crystal," which it is, however, only as 

 resembling colourless quartz in hardness and transparency, not in shape 

 or in structure, seeing that it is essential to good glass not to possess the 

 properties of any crystal, but certain quite different properties. Let us 

 very briefly consider wherein the difference lies. A crystal, such as the 

 six-sided pyramid of quartz, or the eight-faced double pyramid (octo- 

 vol. iv. u u 



