Lesson 13 special glasses let’s Debate about glasses a What is the ingredient of glasses?

LESSON 13
SPECIAL GLASSES

1. let’s Debate about GLASSES.
a) What is the ingredient of glasses?
b) What’s the duty of glasses?



2.Read the text translate and retell.
Besides the common types of glass, there are hundreds of special types. The process of crystallization in a glass is generally avoided; however, in some cases it is desired. The new Pyroceram, shaped in the same manner as an ordinary glass, and then, by appropriate heat-treatment, converted to a completely crystalline material, is an example. Another special glass is sensitive to light, which creates a latent image within the glass; the image is developed by heat-treatment. This glass is used to make signs, and radio and clock faces. A variant of this glass is one in which the portion exposed to light is more soluble than the unexposed portions. So-called solder glass has a relatively low softening point (below 500^ºC). It is used to join the pieces of higher- melting glass without softening and deforming them. The solder glass is applied to the joint as a powder and melted to produce a seal, in a vacuum tube.
Umumiy shisha turlaridan tashqari, yuzlab maxsus turlari mavjud. Stakandagi kristallanish jarayoni odatda oldini oladi; ammo, ba'zi hollarda, bu orzu qilingan. Oddiy shisha bilan bir xil shaklga ega bo'lgan, keyin esa tegishli issiqlik bilan ishlov berish natijasida butunlay kristalli materialga aylantirilgan yangi Pyroceram bunga misoldir. Yana bir maxsus stakan yorug'likka sezgir bo'lib, shisha ichida yashirin tasvirni yaratadi; tasvir issiqlik bilan ishlov berish orqali ishlab chiqilgan. Bu oynadan belgilar, radio va soat yuzlari yasaladi. Ushbu stakanning varianti yorug'lik ta'sirida bo'lmagan qismlarga qaraganda ko'proq eriydi. Lehim oynasi deb ataladigan narsa nisbatan past yumshatilish nuqtasiga ega (500ºC dan past). U yuqori eriydigan shisha bo'laklarini yumshatmasdan va deformatsiya qilmasdan birlashtirish uchun ishlatiladi. Lehim oynasi bo'g'inga kukun shaklida qo'llaniladi va vakuumli naychada muhr hosil qilish uchun eritiladi.