EECREATIVE SCIENCE. 



23 



Therefore, although the soluble glass is de- 

 scribed as being corrosive, experiments should 

 be carried out as to its applicability to the 

 improvement or preservation in any way of 

 photographs on glass, paper, or porcelain ; 

 tlio suggestion of which was one of the 

 main objects in introducing this subject 

 under its present heading. 



Let us now, before considering some ap- 

 plications more foreign to our own subject — 

 photography — see if we can get a closer 

 philosophical insight into this strange and 

 useful thing, soluble glass, or tetra-silicate of 

 cither potash or soda. Its essential basis is 

 the non-metallic element, silicon — or sili- 

 cium, as it has been called by some, from 

 its supposed metallic nature. Berzelius de- 

 scribed silicon to be a brown powder, 

 and judging of it in this condition, he 

 compared it with carbon and boron, two 

 other non-metallic elementary bodies. How- 

 ever, as aluminium, the new white metal, the 

 basis of alumina and of clay, turned out to be 

 metallic, it might be that silicon, the basis 

 of silica, would also have to be classed 

 with the metals. The researches of the 

 distinguished Prench chemist, M. Deville, 

 on aluminium, have, however, led to the 

 production of many-sided crystalline plates 

 of silicon, translucent and nearly colourless, 

 not having any of the ordinary metallic pro- 

 perties. We must now, therefore, view silicon 

 as a non-metal, and group it with boron and 

 carbon, to which it has several points of 

 resemblance. 



This silicon, obtained by the action of 

 aluminium and heat on silicious materials, 

 burns in oxygen gas to form a white powder, 

 the oxide of silicon, or silica, or silicic acid, 

 as it is vai'iously termed. Pure rock-crystal, 

 opal, beryl, chalcedony, hornstone, jasper, 

 quartz, flint, sand, part of all clays, etc., 

 consist of this silica or silicic acid ; indeed, 

 it is one of the most abundant things in 

 nature, as may be at o-nce observed from this 

 description of it. It is in one state sobible 



in water, and is found in parts of plants, 

 animals, and animalcules, and notably in. 

 the canes, grasses, and stalks of cereals. 

 This silica, or pure flint, fuses under the 

 oxy hydrogen blowpipe to a clear bead; when 

 fused, it may be drawn out into long threads 

 like glass ; dropped in a state of fusion into 

 water it solidifies to a transparent mass, 

 free from flaws, and remarkably hard and 

 tough, so that it sustains the blow of a ham- 

 mer without breaking. It seems to harden, 

 like steel, by sudden cooling. Silica can be 

 evaporated from solution by steam. The 

 Geyser tubes of Iceland owe their formation 

 to the fact of the possible solubility and 

 volatility of silica, joined to its peculiar 

 power of losing this solubility under freslx 

 circumstances. Silica is tasteless, inodorous, 

 and, though chemically an acid, is without 

 action on vegetable colours. It can, under 

 certain conditions, combine with water to 

 form a hydrated silicious jelly. The so- 

 luble form of silica, obtained by preci- 

 pitation from a silicate, loses its solubility by 

 simple evaporation at a boiling heat, or little 

 more. The varied and remarkable properties 

 of silica must undoubtedly lead to further 

 applications in practical manufacturing hands. 

 The water-glass is the main door by which a 

 practical man may best enter. 



The silicic acid, or silica, being understood 

 to be an acid, we can now see at once that, like 

 other acids, it may form " salts." Soap is a 

 stearate of soda — stearic acid and soda. This 

 salt is miscible with water, while the acid of 

 the salt, the fat, is not. So, in the same way, 

 silicic acid, in its insoluble form, is made 

 miscible with water by means of an alkali- 

 potash or soda. In both cases stronger agents 

 can throw out the combined acids, and, as we 

 shall see in the case of water-glass, with novel 

 and highly useful results. Even bodies not 

 acid, as sal ammoniac, etc., can throw down 

 the silica under useful conditions. But the 

 scientific details and marvels of silica are ex- 

 haustless, and the eager student must pursue 



