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his eyes , and leads him into the marshy mazes of error . In the preceding investigations , Dr . Priestley followed those methods of collecting aeriform fluids over water , which Hales and others had
employed before him : he now ascertained that there were some gases absorbed by or soluble in water . Mr . Cavendish , one of the most eminent philosophers of that day , had announced this circumstance , and was puzzled by it ; but Dr . Priestley , with
his usual and dexterous ingenuity , overcame the difficulty , by eixiplojing quicksilver instead of water , over which fluid metal he preserved and examined several kinds of air , which are instantly deprived of their elastic state by the contact of water .
The first permanently elastic fluid of this description which he examined , was the muriatic acid ; he obtained it by heating' copper in the fluid acid , or common spirit of salt , and called it marine acid air .
He immediately ascertained its absorption by water , and its powerful acidity ; he found it incapable of supporting : flame , and extremely desfructive of animal life . He examined the
action of a variety of substances upon this gas , and ascertained the remarkable rapidity with which it is absorbed by charcoal , and several vegetable and animal substances . Some
unsuccessful attempts were made to ascertain the specific gravity of this gas , from which Dr . Priestley correctly concluded , however , that it was a little heavier than air . The success attending these experiments * and the readiness with which
he procured and retained the gaseous muriatic acid , led hirn to extend his trials to other acids , when he found , that , by acting upon vitriolic acid by inflammable substances , he could procure from it a permanently elastic fluid , to which he gave the name of
vitriolic acid air ; he found that , like the marine acid air , it was rapidly absorbed by water , and must be collected and preserved over quicksilver ; tivut it was nearly twice as heavy as
afciftospheric air ; that it extinguished flame , and was instantly fatal to animal life 5 that it reddened vegetable blues , and destroyed most colours . This air is , in fact , produced by burning sulphur in the atmosphere , and straw ,
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wool , and other materials , are frequently bleached by exposing them to its fumes . * Having thus obtained permanent aeriform fluids , having- acid qualities , it occurred to Dr . Priestley , that the volatile alcali , the substance which gives pungency to salvolatile , spirit of hartshorn , and similar compounds ,
* Having * elsewhere praised Dr . Priestley ' s candour , I insert the following * extract from his history of the discovery of Vitriolic Acid Air , to shew the exactness with which he acknowledges the hints and assistance of others :
My first scheme was to endeavour to get the vitriolic acid in the form of air , thinking- that it would , probably , be easy to confine Ft by quicksilver , for , as to the nitrous acid , its affinity with quicksilver is so great that I despaired of being- able to confine it to any purpose . I , therefore ,
wrote to my friend Mr . Lane , to procure me a quantity of volatile vitriolic acid , " &c . " Seeing Mr . Lane the winter following * , he tohl me , that if I would only heat any oily or greasy matter with oil of
vitriol , I should certainly make it the very thing I wanted , viz . the volatile or sulphureous vitriolic acid ; and , accordingly , I meant to have proceeded upon this hint , but was prevented from pursuing * it by a variety of engagements .
" Some time after this I was in company with Lord Shelburne , at the seat of Mods . Trudaine , at Montigny , in France ; where , with that generous and liberal spirit by which that nobleman is distinguished-, he has a complete apparatus of philosophical instruments , with every other convenience
and assistance for pursuing * such philosophical inquiries as any of his numerous guests shall choose to entertain themselves with . In this ag-reeable retreat I met with that eminent philosopher and chemist , Mons . Monti g-ni , Member of the Royal Academy of Sciences ; and conversing with
Imn upon tins subject , he proposed our trying to convert oil of vitriol into vapour , by boiling it on a pan of charcoal in a cracked phia . 1 . This scheme not answering our purpose , he next proposed heating " it together with oil of turpentine .
Accord ing-ly , we went to work upon it , and soon produced some kind of air confined with quicksilver ; ]> ut our recipient being overturned by the suddenness of the production of the air , we were not able to catch any more than the first produce , which was little else than the common air
which had lodged on the surface of the liquor , and which appeared to be a little , phlog-isticated by its not facing much affected by a mixture of nitrous air , "
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68 £ Mr . Brandes Estimate ofDr * Priestley ' s Chemical Discoveries *
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), Nov. 2, 1818, page 682, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2482/page/18/
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