首页
登录
职称英语
Glass is made of mixture of many substances melted together in a large furna
Glass is made of mixture of many substances melted together in a large furna
游客
2023-10-04
13
管理
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 and charcoal. Acids are used to remove iron and other impurities. Which might discolor the glass.
The heat of the furnace is so intense that the mixture of these various materials is changed into a boiling liquid. How is liquid glass formed into beautiful or useful objects? Let us imagine that we are watching things being made in a glass factory. It is a small factory in which the work is still done by craftsmen and not by machinery.
Here is a man holding a long iron tube called a blow-pipe. The tube has a wooden mouth-piece to protect the man’s lips from the heat. He puts the other end of the pipe into the molten glass and picks up some of the mixture on the end of the tube. Then he robs the lump of glass to and fro on a metal table, rather like a person rolling pastry. As he rolls it, he shapes the lump roughly into the required form.
Next he lifts the pipe, puts the wooden end to his lips, puffs out his cheeks and blows as you do when you are blowing up a balloon. But of course he has to blow much harder. When the air is blown down into the lump of molten glass a gorge bubble is gradually formed. The craftsman needs both powerful lungs and great skill to ensure that the bubble is of exactly the required size and thickness.
Now you understand why so many hand-made glass objects are round in shape. Handles and feet must be added while the glass is still plastic. When the object is shaped to the craftsman’s satisfaction, it is allowed to cool off. The cooling must be done very gradually. As you know, glass is cracked by extreme and sudden changes of temperature.
Some of the loveliest and many of the most useful things in the world are made of glass. It is most surprising, in view of the great technical skill required, that glass making is a very ancient art. It was practiced thousands of years ago by ancient Egyptians although it was many centuries before men discovered how to make glass transparent.
Glass Making
To remove impurities from the glass,【46】.
Craftsman rolls the molten glass【47】on a metal table.
Glass objects are made【48】.
The mouth-piece of the blow-pipe is【49】.
All glass is【50】.
[br]
选项
答案
backwards and forwards
解析
转载请注明原文地址:https://www.tihaiku.com/zcyy/3069868.html
相关试题推荐
WhatdidPetergettogetherwiththeletterof18,July?______andworkglov
WhatdidPetergettogetherwiththeletterof18,July?______andworkglov
Theteacher,togetherwithherstudents,(go)______tothebeachtoswim.goes句子
Theteacher,togetherwithherstudents,(go)______tothebeachtoswim.goes句子中主
Themanager,togetherwithhissecretary,often(go)______abroadtoexplorethe
Thetwo______(develop)countriesarenowworkingtogethertoimprovetheireconom
Ireallyenjoy(work)______togetherwithyou,andthankyouforyourcooperation
Wewouldliketohavesamplesofvarioussizesofyourproducttogetherwiththe
Socialchangeismorelikelytooccurinsocietieswherethereismixtureof
Socialchangeismorelikelytooccurinsocietieswherethereismixtureof
随机试题
Mostpeoplewouldbe【71】bythehighqualityofmedicine【72】tomostAmericans
Choosethecorrectletter,A,BorC.ReflectiveJournalAssignment[br]Whatis
ModesofTransportationThereareavarietyofmeansfortrans
Atthebeginningofthetwentiethcentury,NorthAmericansocietyheld,asa
与其他专业审计相比,建设项目审计尤其自身固有的特点,主要表现在()。A.审计范围
A.生白术 B.炙甘草 C.人参 D.炒山药 E.西洋参善治气虚心动悸的
Thechangeinthatvillagewasmiraculou
属于渗透性利尿药的是A.依他尼酸 B.甘露醇 C.螺内酯 D.氨苯蝶啶
9月10日,白糖现货价格为6200元/吨。某糖厂决定利用白糖期货对其生产的白糖进
关于选择性产业政策效果,错误的是( )。 A.奠定了国家产业发展的早期基础
最新回复
(
0
)