pneumatic trough, glass collecting cylinders , other equipment used priestley in experiments on gases. right-hand cylinder exhibits sprig of mint showed plants generated oxygen carbon dioxide
priestley s first volume of experiments , observations on different kinds of air outlined several important discoveries: experiments lead discovery of photosynthesis , discovery of several airs: nitrous air (nitric oxide, no), vapor of spirit of salt (later called acid air or marine acid air ; anhydrous hydrochloric acid, hcl), alkaline air (ammonia, nh3), diminished or dephlogisticated nitrous air (nitrous oxide, n2o), , dephlogisticated air (oxygen, o2). priestley developed nitrous air test , tested goodness of air : using pneumatic trough , mix nitrous air test sample, on water or mercury, , measure decrease in volume—the principle of eudiometry. after small history of study of airs, explained own experiments in open , sincere style: whatever knows or thinks tells: doubts, perplexities, blunders set down refreshing candour. invented , described cheap , easy-to-assemble experimental apparatus. colleagues therefore believed reproduce priestley s experiments verify them or answer questions had puzzled him.
although many of results puzzled him, priestley used phlogiston theory resolve difficulties. theory, however, led him conclude there 3 types of air : fixed , alkaline , , acid . priestley ignored burgeoning chemistry of day, indeed dismissing in these volumes. instead, focused on gases , changes in sensible properties , had natural philosophers before him. isolated carbon monoxide (co) seems not have realised separate air others had discovered.
discovery of oxygen
after publication of first volume of experiments , observations, priestley undertook set of experiments. in august 1774 isolated air appeared new, did not have opportunity pursue matter because tour europe shelburne. while in paris, however, priestley managed replicate experiment others, including antoine lavoisier. after returning britain in january 1775, continued experiments , discovered vitriolic acid air (sulphur dioxide, so2). in march wrote several people regarding new air had discovered several months earlier. 1 of these letters read aloud royal society, , published paper in philosophical transactions titled account of further discoveries in air. priestley called new substance dephlogisticated air , described 5 or 6 times better common air purpose of respiration, inflammation, and, believe, every other use of common atmospherical air. had discovered oxygen gas (o2). revised experiments , observations, paper begins:
the contents of section furnish striking illustration of truth of remark have more once made in [natural] philosophical writings … more owing call chance—that is, philosophically speaking, observations of events rising unknown causes proper design or preconceived theory in business. … own part, frankly acknowledge @ commencement of experiments recited in section far having formed hypothesis led discoveries made in pursuing them have appeared improbable me had been told of them; , when decisive facts did @ length obtrude upon notice slowly, , great hesitation, yielded evidence of senses. [emphasis priestley s]
priestley assembled oxygen paper , several others second volume of experiments , observations on air , published in 1776. not emphasise discovery of dephlogisticated air (leaving part iii of volume) instead argues in preface how important such discoveries rational religion. paper narrates discovery chronologically, relating long delays between experiments , initial puzzlements. thus, difficult determine when priestley discovered oxygen. such dating significant lavoisier , swedish pharmacist carl wilhelm scheele both have strong claims discovery of oxygen well, scheele having been first isolate gas (although published after priestley) , lavoisier having been first describe purified air entire without alteration (not dephlogisticated air ).
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