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Such were Dr . Priestley ' s researches , and such the views to which he had been led previous to the year 1773 , when he undertook the examination of the air which rises from red lead , and from red precipitate of quicksilver , when those substances are
exearth . We knew before that putrid animal substances were converted into sweet vegetables when mixed with the earth and applied as manure ; and now , it seems that the same putrid substances , mixed with the air , have a similar effect . The strong' thriving state of your mint , in
putrid air seems to shew that the air is mended by taking" something * from it , and not by adding * to it . I hope this will give some check to the rage of destroying trees that grow near houses , which has accompanied our late improvements in gardening ,
from an opinion of their being unwholesome . I am certain , from long observation , that there is nothing unhealthy in the air of woods ; for we Americans have every where our country habitations in the midst of woods , and no people on earth enjoy better health , or are more prolific . " Phil . Trans . 1772 , page 199 .
Notwithstanding these researches , which have exposed some very curious facts relative to the chemical physiology of plants , it must be confessed that the causes of the renovation and equality of our atmosphere are yet by no means ascertained ; for , although some growing vegetables do , under certain circumstances , purify the
air , ( by the absorption of carbon and the evolution of oxygen , ) yet , when in a state of decay , they invariably add to its contamination , and a general view of the subject would induce us to conclude , that they do as much harm as good , at least , if recent experiments connected with this subject are to be considered as correct .
These are the prominent features- of Dr . Priestley ' s first communication to the Royal Society respecting the different kinds of air , and had he bestowed no other contribution upon chemistry , the facts here detailed would have entitled him to > a
conspicuous place among the benefactors of the science . The paper is divided into several sections , in which lie discusses the nature and properties of fixed air ; of the air contaminated by the combustion of candles and of brimstone ; of inflammable
air ; of air infected with animal respiration or putrefaction ; of air exposed to the action of mixtures oC iron filings and sulphur ; of nitto&s air ; of air in which metals have been calcined , and which has been exposed to the action of white-lead paint and of air procured by spirit of salt .
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posed to heat . This , indeed , was one of the topics upon which Hales had touched before him , but it was passed over with that hasty and superficial carelessness of which his experimental proceedings furnish so many instances , and in which he so often
lost the substance by grasping at the shadow . Dr . Priestley cast his keenest eye upon the prospect now before him , and as the various objects came into view , he followed them up with more
than his ordinary diligence and usual sagacity . The track he had entered upon was , indeed , of such abundant promise , as would have insnared the attention and excited the curiosity of one less awake than our author to its
interest and novelty . But he , already well initiated * in the management of aeriform fluids , proceeded with a rapidity which left his associates far behind , and carried him , in proud and undisputed precedence , to the goal of discovery .
The 1 st of August , 1774 , is a redletter day in the annals of Chemical Philosophy , for it was then that Dr . Priestley discovered , dephlogisticated air . Some , sporting in the sunshine of rhetoric , have called this the birthday of Pneumatic Chemistry ; but it was even a more marked and
memorable period ; it was then ( to pursue the metaphor ) that this branch of the science , having eked out a sickly and infirm infancy in the ill-managed nursery of the early chemists , began to display symptoms of an improving constitution , and to exhibit the most
hopeful and unexpected marks of future importance . Dr . Priestley ' s original opinion , that all kinds of factitious air were noxious , seems first to have been shaken by observing that a candle would burn in air procured by distilling nitre in a
gun barrel ; but the first experiment , which led to a very satisfactory result , was conducted as follows : A glass y <\ r was filled with quicksilver , and inverted in a basin of the same ; some red precipitate of quicksilver was then
introduced , and floated upon the quicksilver in the jar ; heat was applied to it in this situation by a burning lens , and " I presently found that air was expelled from it very readil y * Having got about three or four times as much as the bulk of my materials , I
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itfr . Urandes Estimate of Dr . Priestley $ C / iemical Discoveries . 679
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), Nov. 2, 1818, page 679, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2482/page/15/
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