Nature and characters of GLASS. Naturalists are divided in what class of bodies to rank glass: some making it a concrete juice; others a stone; others again rank it among semi-metals; but Dr Merret observes,
that these are all natural productions, whereas glass is a fictitious compound, produced by fire, and never found in the earth, but only the sand and stone that form it: that metals are formed by nature into certain species; and that fire only produces them, by its faculty of separating heterogeneous, and uniting homogeneous bodies: whereas it produces glass, by uniting heterogeneous matter, viz. salt and sand, of both which it evidently consists; 100 lb weight of sand yielding above 150 lb of glass.
The same learned doctor gives us a precise and accurate enumeration of the several characters, or properties of glass, whereby it is distinguished from all other bodies, viz. 1. That it is an artificial concrete of salt and sand, or stones. 2. Fusible by strong fire. 3. When fused, tenacious and coherent. 4. It does not waver nor consume in the fire. 5. When melted, it cleaves to iron. 6. When it is red hot, it is ductile, and may be fashioned into any form; but not malleable; and capable of being blown into a hollowness, which no mineral is. 7. Frangible when thin, without annealing. 8. Friable, when cold. 9. Diaphanous, whether hot or cold. 10. Flexible and elastic. 11. Diffoluble by cold and moisture. 12. Only capable of being graven or cut with a diamond, or other hard stone and emery. 13. Receives any dye or colour both externally and internally. 14. Not diffoluble by aqua fortis, aqua regia, or mercury. 15. Neither acid juices nor any other matter extract either colour, taste, or any other quality from it. 16. Admits of polishing. 17. Neither loses weight nor substance by the longest and most frequent use. 18. Gives fusion to other metals, and softens them. 19. The most pliable thing in the world, and that which best retains the fashion given it. 20. Not capable of being calcined. 21. An open glass being filled with water in the summer-time, will gather drops of water on the outside, just so far as the water on the inside reaches; and a person's breath blown on it will manifestly moisten it. 22. Little glass balls filled with water, mercury, and other liquor, and thrown into the fire, as also drops of green glass being broken, will fly afunder with a great noise. 23. Neither wine, beer, nor any other liquor, will make it musty, or change its colour, or rust it. 24. It may be cemented, as stones and metals. 25. A drinking glass, partly filled with water, and rubbed on the brim with a wet finger, yields musical notes, higher or lower as the glass is more or less full, and will make the liquor frisk and leap.