An example of an (historical) idea mooted by a scientist that would today be considered an alternative conception.
"In 1766 Henry Cavendish … dissolved marble in hydrochloric acid, producing Black's 'fixed air'; … He also produced hydrogen by dissolving either zinc or iron or tin in sulphuric or hydrochloric acid, and found that there was no difference in the gas if he used different acids on the metals; and again he calculated its specific gravity. It was clear, therefore, that these two gases had a stable existence, and could be produced with permanent properties – they were not the capricious result of some more inconstant impurities in the air. …Even now, however, there was a feeling that in the last resort only one kind of air really existed common air and that the varieties were due to the presence or absence of phlogiston. Cavendish was inclined to identify his 'inflammable air' with phlogiston, though there were objections to this, since phlogiston had been assumed to be not the burning body itself but a substance that left the burning body – and if the hydrogen was phlogiston how could phlogiston leave itself?…
Cavendish came to the conclusion that hydrogen must be water deprived of its phlogiston and oxygen must be phlogisticated water."
Herbert Butterfield (1957) The Origins of Modern Science 1300-1800 (New Edition: Revised and enlarged). G. Bell and Sons Ltd., London.
