Breath of life: the evolution of oxygen therapy

Between 1771 and 1772 the Swedish pharmacist Karl Scheele did a series of experiments with mercuric oxide and potassium nitrate.On heating the two he obtained a gas that caused candles to burn more brightly.He did not, however, rush to publication.By the time the observation was published, in 1777, Scheele had been overtaken by the English theologian-chemist Joseph Priestley.Working independently in 1774, Priestley had heated mercuric oxide and obtained what he described as 'dephlogisticated air'-an experiment reported in 1775.The gas discovered by Scheele and Priestley was oxygen-the agent ubiquitous in modern medicine. PHLOGISTON THEORYPriestley's nomenclature was derived from the 'phlogiston' theory-the chemical wisdom of the time.This theory stated that fires released their phlogiston or combustible components into the atmosphere.By gently heating a burnt substance such as mercuric oxide, Priestley believed he was removing phlogiston from the atmosphere into the mercury, so purifying the air.Hence the term dephlogisticated air, which he describes inhaling in his Experiments and Observations on Different Kinds of Air: 1 'The feeling of it to my lungs was not sensibly different from that of common air; but I fancied that my breast felt peculiarly light and easy for some time afterwards.Who can tell but that, in time, this pure air may become a fashionable article in luxury.Hitherto only two mice and myself have had the privilege of breathing it.'