XI. Прочитайте текст. Выберите предложения, соответствующие его содержанию. Используйте T (true) – соответствует; F (false) – не соответствует A Wonder Metal The story of titanium is extraordinary. To begin with, it was discovered twice. A British scientist, William Gregor, found it first and called it menachanite, and six years later, in 1797, M.H. Klaproth, a German chemist, also found it and gave it its present name. For many years, titanium was of inretest only to research chemists – it was considered too brittle1 to be of any practical value. Yet it was the impurities2 with which it was usually associated (it forms compounds easily with nearly every known element) that made it brittle. It cost the chemists in many countries endless efforts to isolate pure titanium and even more to start producing it commercially. In 1948 the world stock of pure titanium was only ten tons. Today the output is much larger. Titanium has one surprising property – it is completely inert in biological media, something the medical community was quick to notice. It is being used to make artificial joints3 and many other things necessary in surgery at the Priorov Central Institute of Traumatology and Orthopedics. Titanium instruments do not corrode, and are thirty per cent lighter than instruments made of stainless steel. Titanium’s high standard of corrosion resistance, lightness, tensile strength4, and the ease of forging, rolling and stamping are finding it more and more uses. Titanium alloys are very useful in mechanical engineering, and for chemical and refectory5 apparatus. Titanium helped Soviet design engineers to surmount the sound and heat barriers in supersonic and high-altitude aircraft designing. On earth, it shows good work at chemical plants, in the pulp-and-paper and food industries. Moreover, it is still a source of surprise for the investigator. Notes: 1brittle – хрупкий 2impurities - примеси 3 artificial joints - искусственные суставы 4 tensile strength – прочность на разрыв 5refractory – огнеупорный 41. Titanium, to say, was discovered twice. 42. Its present name this metal was given at the end of the 18th century. 43. Titanium was always considered to be of great practical value 44. It was the impurities that made titanium brittle. 45. It took the chemists great efforts to start commercial production. 46. Only some years ago the world stock of pure titanium was about 10 tons. 47. Titanium is very active in biological media. 48. Titanium items are much lighter than those made of stainless steel. 49. Owing its majestic properties titanium is used more and more widely. 50. Titanium alloys are not produced at industrial scale.