Question

In 1772, Joseph Priestley demonstrated that
(A) Plants foul the air
(B) Animals purify the air during day time
(C) Plants and animals restore air for each other
(D) Plants get killed in the air produced by animals

Answer 1

Joseph Priestley cannot be limited to the scientific community. He was a chemist, taught many subjects, philosopher, grammarian and was also interested in politics. He systematically studied many gases in the atmosphere.

Complete answer:
Joseph Priestly was far ahead of his times. He prepared and observed the characteristics and behavior of various gases in his laboratory. The gases which he prepared were hydrogen, Sulphur dioxide, nitric oxide, carbon monoxide, oxygen, ammonia, hydrogen chloride, nitrogen dioxide, and nitrogen.
In 1770, Priestley observed that when a burning candle was kept in a closed space with no air circulation, the flame went off sometime. Similarly, a mouse in such conditions suffocated and died. This intrigued him. He then kept a mint plant along with a burning candle in a closed space. He was surprised to discover that it burned longer. Similarly, when mint plants and mice were kept in closed space they survived too.

In this way, in 1772, Joseph Priestley demonstrated that (C) Plants and animals restore air for each other.

Note:
Priestley believed and defended the “Phlogiston theory”. According to this superseded theory, during combustion a fire like element is released from the combustible bodies. The element was named phlogiston from which the theory gets its name.
He was credited for the discovery of oxygen in a gaseous state. However, his claims were different. He produced oxygen by directing sun’s rays on mercury oxide through glass. The oxygen produced, as observed by him, did not dissolve in water but it fueled the combustion. As a phlogiston theory believer, he proposed that oxygen promotes combustion as it has negligible amount of phlogiston within them and named oxygen as ‘dephlogisticated gas’ and nitrogen, which does not promote combustion, as ‘phlogisticated gas’.