Glass

a hard, brittle, transparent substance, formed by fusing together mixtures of the silicates of potash, soda, jlime, magnesia, alumina, and lead in various proportions, according to the quality or kind of gla required. Of the origin of gla manufacture we cannot speak with certainty. Pliny states that the ancient Phenic i ans discovered by a happy accident how to make it. He relates that certain Pheenician merchants preparing a meal upon the seashore set their cooking ve el on a ma of natron (sub carbonate ‘of soda) and the union of the sand and alkali, when subjected to the fire, resulted in vitrification that drew the men’s attention and led to subsequent efforts at imitation. According to Egypt ologists the Egyptians made sham jewels of gla at least 5,000 or 6,000 B. c. In some of the most ancient tombs scarabs of gla have been found imitating rubies, emeralds, sapphires, and other precious stones, and the gla beads found broadcast in three parts of the globe were quite po ibly pa ed off by traders on confiding barbarians as jewels of great price. As a medium of trade, beads are evidently of great antiquity. Those known as aggry have been attributed to both Egyptian and Phenic i an sources. The beads vary greatly in color and pattern and some of them show fine workmanship and marked beauty. During the period when Egypt was part of the Roman empire much gla was produced in the Nile valley. It is uncertain whether gla was made in England before the 16th century, as that mentioned may have been imported from Flanders or Vénice. In 644 Benedict Biscop introduced makers of gla windows into Nor thumb ria; but window gla was not in general use for windows till the 15th century. Attempts were made to establish gla works at James town, Va., in 1608-1622; at Salem, Ma ., in 1639-1640; in New York city before 1664; and in Pennsylvania betore 1683. Subsequently works were established in 1780 at Temple, N. H.:; in 1792 at Boston; and in 1797 at Pittsburg. Plate gla was first made there in 1853, and it is also made at Baltimore and New York. Pre ed gla was invented in the United States. Gla making is now a most flourishing American industry.