Air, dephlogisticated

These included Scheele, Cavendish, Priestley, and others. They called it burnt or dephlogisticated air," which meant air without oxygen. 

Priestley believed that all materials contained an element called phlogiston , which was given off when they burned. Air in which things had been burned became less able to support combustion because it was then saturated with phlogiston . Accordingly, Priestley called his gas, in which a candle flame burned brightly, dephlogisticated air . 

His name for hydrogen was inflammable air. However, he had no doubt that this gas he had discovered was phlogiston. In science, theory often determines what we observe. Cavendish was simply interpreting his results in terms of the accepted theory of his day. He was far from the only scientist who did so. For example, when Priestley discovered oxygen, he named it dephlogistated air. ... 

Joseph Priestley found that the constituent of the atmosphere which restores the bright red color to the dark blood is dephlogisticated air (oxygen) (202). Although Fourcroy and Vauquelin believed that the iron in the blood was combined as a phosphate, it is now known to be present in a far more complex compound, hemoglobin (205). M. O. Schultze found that analyses of hemoglobins of different species yielded concordant values of 0.335 per cent of iron (206). 

As early as 1771 Joseph Priesdey noticed that this process purified the air, and in 1778 he identified the gas as dephlogisticated air (oxygen) (40). I have been so happy, said he, as by accident to have hit upon a method of restoring air which has been injured by the burning of candles, and to have discovered at least one of the restoratives which nature employs for this purpose. It is vegetation.. . . Finding that candles would bum very well in air in which plants had grown a... 

Dephlogisticated Air term Priestley used for oxygen, air devoid of phlogiston Dephlogisticated Nitrous Air term Priestley used for nitrous oxide, N O, laughing gas... 

Obviously, thought Priestley, the air was peculiarly lacking in phlogiston, and was therefore especially avid to soak it up from burning substances. Priestley never swayed from his firm conviction in the phlogiston theory as long as he lived, and he called his new gas dephlogisticated air . 

So Priestley s dephlogisticated air had a hidden past. Scheele s work was still unknown in 1775, since the apothecary did not announce his findings (which included the fact that fire air comprised one-fifth of common air) until 1777-... 

Seeing this report, Priestley realized that Lavoisier had not quite appreciated the superior qualities of his dephlogisticated air - it was not merely common air. He sent the Frenchman a sample of the gas to verify that this was so. As a result, Lavoisier presented a paper to the French Academy in April in which he identified the principle of combustion - Priestley s gas - as an especially pure air . In keeping with his notorious arrogance, he made no mention of the contributions of Priestley and Bayen. 

Materials will burn only in that kind of air which Mr. Priestley has named dephlogisticated air and which I name here pure air. ... 

In the foregoing essays I have endeavoured to prove as clearly as is possible by physics and chemistry, that the very pure air which Dr. Priestley has denominated dephlogisticated air, enters, as a constituent part, into the composition of several acids, and especially into that of the phosphoric, vitriolic, and nitrous acids. 

We have also seen that Lavoisier identified dephlogisticated air as the principle of acidity, and accordingly renamed its material substance oxygen. And in parallel to Macquer s phlogiston, Lavoisier s oxygen principle was known to be infallibly present in acids, but its presence did not necessarily confer acidity on all bodies that contained it. Let us briefly examine the use of principles that was so common in chemical descriptions of the seventeenth and eighteenth centuries, and compare it with Lavoisier s use of the principle of acidity. 

We may safely conclude, [be says] that in the present experiments the phlogisticated air was enabled by means of the electric spark to unite to form a chemical combination with the dephlogisticated air, and was-thereby reduced to nitrous (that is, our nitric ) acid, which united to the soap-lees and formed a solution of nitre.. .. A fur-thur confirmation of it is, that, as far as I can perceive, no diminution of air is produced when the electric spark is passed either through pure dephlogisticated air, or through perfectly phlogisticated air, which indicates the necessity of a combination between these two airs to produce the acid. ... 

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