sawulja123D

08.04.2020 23:20 •  Английский язык

Составить вопросы разных типов по тексту. (максимум 20=)) from the earliest times, men have observed most striking changes that take place in nature and have made accidental discoveries of great value. many of the substances used today, which are prepared by chemical methods, were known to the ancients, but there are no historical records of their discovery. glass, for example, has been known for over 3,000 years. soap was also made in the earliest times. directed experimentation appeared with the rise of alchemy. the alchemists sought things which were supposed to lead to happiness – health and riches. they wanted to change the common metals into gold hoping to do this with the help of a mysterious substance, called the philosopher’s stone. but gold without health is of little value, so a search was made for the elixir of life which could bring back glorious youth to the aged. the alchemists studied everything available, mixed things together, heated and distilled them when possible. many important discoveries were made as a result of eager search by the alchemists for what was unattainable, and some of the processes used today in chemistry were invented. they referred repeatedly to distillation, extraction, calcinations, coagulation, etc. they prepared and studied many of the compounds which are commonly used in chemical work. among these are sulphuric, nitric, and hydrochloric acids, alum, soda, ammonium chloride, niter, and compounds of mercury, arsenic and antimony. but selfish and utilitarian motive which guided the alchemists could not lead to the development of a science. chemistry was born as a science only at that time when a desire on the part of man to learn the truth about the wonders of nature appeared.