write the contribution of the following scientists.
1) Joseph Priestley
2) Von Hamelton
3)Joseph Black.
Answers
JOSEPH PRIESTLEY:
American Chemical Society, Chemistry for Life ®
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Joseph Priestley and the Discovery of Oxygen
International Historic Chemical Landmark
Dedicated August 1, 1994, at the Joseph Priestley House in Northumberland, Pennsylvania, USA, and August 7, 2000, at Bowood House in Wiltshire, UK.
Landmark Lesson Plan: Joseph Priestley, Discoverer of Oxygen
When Joseph Priestley discovered oxygen in 1774, he answered age-old questions of why and how things burn. An Englishman by birth, Priestley was deeply involved in politics and religion, as well as science. When his vocal support for the American and French revolutions made remaining in his homeland dangerous, Priestley left England in 1794 and continued his work in America until his death.
In a series of experiments culminating in 1774, Priestley found that "air is not an elementary substance, but a composition," or mixture, of gases. Among them was the colorless and highly reactive gas he called "dephlogisticated air,
On August 1, 1774, he conducted his most famous experiment. Using a 12-inch-wide glass "burning lens," he focused sunlight on a lump of reddish mercuric oxide in an inverted glass container placed in a pool of mercury. The gas emitted, he found, was "five or six times as good as common air." In succeeding tests, it caused a flame to burn intensely and kept a mouse alive about four times as long as a similar quantity of air.
Priestley called his discovery "dephlogisticated air" on the theory that it supported combustion so well because it had no phlogiston in it, and hence could absorb the maximum amount during burning. (The year before, Swedish apothecary Carl Wilhelm Scheele isolated the same gas and observed a similar reaction. Scheele called his material "fire air." But his findings were not published until 1777.)