Early?Research?on?Air

In?the?field?of?chemistry,?the?understanding?of?the?word?“air”?has?undergone radical?change.?Air?for?John?Mayow,?a?seventeenth-century?chemist,?was?essentially a receptacle?for?airborne?particles,?and?through?them?manifested?a?variety?of?chemical?properties.But?although?Mayow?and?a?few?other chemists did?detect?specific chemical properties in?what we?call?gases?(including?our carbon dioxide),?most?chemists?left them?unaccounted for?until?the?beginning?of the?eighteenth?century.As?chemists became?aware?that the?atmosphere itself?(and not?just particles?within?it) had?a?role?to?play in combustion,?respiration,?and?other?reactions,?they?did?not?attribute?this?to?the?chemical?properties of air but?rather?to?substances that air?could?absorb?and release?according?to?circumstances.Thus, air provided a?physical?environment?in which some reactions?took?place.

In the early?1700s,?the air?was?widely?seen?as?just?such?an environment,?and?“air”?and?“the air”?were one?and?the?same?thing.?Chemists?were?not in the?habit of regarding airs?or?gases?as?having?different?chemical?properties.?There was?simply air. One?obvious reason for?this?was?practical?Chemists could?examine?solids?and?liquids,?exposing?them?to?a variety?of?tests?and?seeing how?they?contributed to?assorted?reactions.?Chemists had,?however,?no?comparable?way?of?examining air;?and they?came to view?chemistry?as?the sum?total?of?the?reactions of?solids?and liquids,?excluding?gases.?Chemists stressed?chemical?qualities?over?physical?properties like weight?and?let physicists?deal?with air.?Chemists generally?did?not examine?air,?and they did not try?to weigh?it. That?does?not mean?that chemists?did not?weigh?substances.?They?did?a lot?of?weighing,?and?pharmacists and?metallurgists?did?more.?But?weighing?gases was outside their?brief.?In the?Encyclopedia of?Diderot?and d‘Alembert,?published?between?1751?and?1775.?readers?were told?that?“the?incoercibility?of?gases?will remove?them?from?our?researches?for?a?long time?to?come.”

By?the?time of the?Encyclopedia,?however, this had?begun?to?change?One?of the first?and?key?sources of?change?was?the invention by?the?Reverend?Stephen?Hales of?a new?instrument,?the?pneumatic?trough.?This instrument?is?important?for?what it?made possible?in?the handling?of air.?The?history?of?its?invention and?early?use illustrates?the difference there?may?be?between?the?motives for?inventing?a?device and?the?ways?in?which?that device?is used.

Hales?was a?botanist?and chemist as well?as?a physiologist.?He wrote?a?book?in?1727?investigating?mechanical?subjects like the?pressure of sap?in?plants.?But?Hales?went?further,?addressing?chemical as?well?as?physiological?questions. He urged?chemists?to?consider?air?chemically.?He?described?an instrument?for?washing?the?air produced?in the?course?of?a?chemical?reaction.?He?wanted to?get?rid?of?impurities?in?the?air?by?letting?it?pass through water.?Air?passed?from?a reaction vessel through?water in?a trough?(or?tube)?and?then?into?a?second vessel?that?was?partly?filled?with?water?and that?could?capture air.

In devising?this apparatus,?Hales?had coincidentally?furnished an instrument?for?catching?and?holding?air,?which?could?then?be?subjected to?various tests.?Used in?this?way the?apparatus?became?known as the?pneumatic trough half?a century after its invention,?it?became a staple?of?the?chemical laboratory.?It?also became one of?the?key instruments in the?reform?of chemistry?that?we?know?as the?chemical?revolution?because it was essential?to?incorporating?a?whole new?state?of?matter,?the?gaseous?state,?into?chemistry,?alongside?the?already?studied?solid?and?liquid?states.?Once that step?had?been?taken,?it was?possible to?speculate and?then to?demonstrate that?the gaseous?state,?like the solid?and?liquid?states,?could?contain?a?variety?of?chemical?substances. This was an enormous?step, and it?did not happen?overnight.?Hales had?shown that air could?be contained,?washed,?and?purified, and tested?chemically as well?as physically.?This,?however, did?not lead?him?to think?that?there?was?more?than one?kind of?air.?Air for him?remained air,?not?one?of?a number?of?airs.?Other chemists would?take that essential step.

1.

?In the field of chemistry, the understanding of the word “air” has undergone radical change. Air for John Mayow, a seventeenth-century chemist, was essentially a receptacle for airborne particles, and through them manifested a variety of chemical properties.But although Mayow and a few other chemists did detect specific chemical properties in what we call gases (including our carbon dioxide), most chemists left them unaccounted for until the beginning of the eighteenth century.As chemists became aware that the atmosphere itself (and not just particles within it) had a role to play in combustion, respiration, and other reactions, they did not attribute this to the chemical properties of air but rather to substances that air could absorb and release according to circumstances.Thus, air provided a physical environment in which some reactions took place.