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New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority. In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali or alkaline earth metal oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition). Evaporation losses during glass melting should be considered during the selection of the raw materials, e.g., sodium selenite may be preferred over easily evaporating SeO2. Also, more readily reacting raw materials may be preferred over relatively inert ones, such as Al(OH)3 over Al2O3. Usually, the melts are carried out in platinum crucibles to reduce contamination from the crucible material. Glass homogeneity is achieved by homogenizing the raw materials mixture (glass batch), by stirring the melt, and by crushing and re-melting the first melt. The obtained glass is usually annealed to prevent breakage during processing.

What is the reason for crushing the glass and melting it again?
Answer: homogeneity
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In the generations after emigration from the west, Jewish communities in places like Poland, Russia, and Belarus enjoyed a comparatively stable socio-political environment. A thriving publishing industry and the printing of hundreds of biblical commentaries precipitated the development of the Hasidic movement as well as major Jewish academic centers. After two centuries of comparative tolerance in the new nations, massive westward emigration occurred in the 19th and 20th centuries in response to pogroms in the east and the economic opportunities offered in other parts of the world. Ashkenazi Jews have made up the majority of the American Jewish community since 1750.

What precipitated the development of the Hasidic movement?
Answer: A thriving publishing industry and the printing of hundreds of biblical commentaries
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St. John's economy is connected to both its role as the provincial capital of Newfoundland and Labrador and to the ocean. The civil service which is supported by the federal, provincial and municipal governments has been the key to the expansion of the city's labour force and to the stability of its economy, which supports a sizable retail, service and business sector. The provincial government is the largest employer in the city, followed by Memorial University. With the collapse of the fishing industry in Newfoundland and Labrador in the 1990s, the role of the ocean is now tied to what lies beneath it – oil and gas – as opposed to what swims in or travels across it. The city is the centre of the oil and gas industry in Eastern Canada and is one of 19 World Energy Cities. ExxonMobil Canada is headquartered in St. John's and companies such as Chevron, Husky Energy, Suncor Energy and Statoil have major regional operations in the city. Three major offshore oil developments, Hibernia, Terra Nova and White Rose, are in production off the coast of the city and a fourth development, Hebron, is expected to be producing oil by 2017.

What years did the fishing industry fall in Newfoundland and Labrador?
Answer:
1990s