Page 144 - Third Book of Reading Lessons

l
2. Putty is a soft, unctuous substance, which hard­ ens by exposure to air, and is used by glaziers to sten the panes of glass to the window- ames. It is composed of linseed oil and whiting; so etimes with the addition of white lead. The whiting is pre­ pared for m chalk, ground into a ne powder; and the oil and white lead are worked into it till all the substances are thoroughly mixed together. Linseed oil is extracted' o the seed of the ax; which in
RE DING LESSONS.
143
and the sand, mixing with the ashes, became vitri ed by the heat. This furnished the merchants with the hint that led to the making of glass, which was rst regularly manu ctured at Sidon in Syria. England is now much celebrated r its glass. The qualities which render this substance so valuable, are, that it is hard, transparent, nearly incrrodible, not being
readily a ected by any substance but acid in a uid state; and that, when sed or melted, it becomes so ductile and plastic, tha it may be moulded into any rm, which it will retain when cool. There are
1 three sors of furnaces used in making it: one to pre­ I pare the frit, a seco d to work the glass, and a third l to anneal it. After having prop·erly mixed the ashes
and sand, they are put into the t rnace, where they are burned or calcined r a su cient time, and become what is called it. This being boiled after­ wards in pots or crucibles of pipe-clay, in the second furnace, is t r the operation of blowing ; the an­ nealing rnace is intended to cool the glass very gradually; r if it be exposed to the cold air imme­ diately after being blown, it will fall into a thousand pieces, as if struck by a hammer. De re glass was
linvented, thin lia of mica or horn were used r
windows.
· Latin is called linitm,. MAYO.