Glass is made of mixture of many substances melted together in a large furnace. The most important substance is silica which is

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问题    Glass is made of mixture of many substances melted together in a large furnace. The most important substance is silica which is found in sand. Potash (钾碱), obtained from wood-ashes, is also necessary. To these two substances are added lime, lead, soda  

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答案entirely by machinery

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