The Progress of Scienti/lc Agri culture. 427 



tlioagh Stalil had been correct in attributing to phlogiston 

 the combustible properties of any solid, it played quite an 

 opposite part when it became incorporated in any gas. There 

 were, he supposed, two constituents of the air, one (after- 

 wards called nitrogen) incapable of supporting combustion 

 because saturated with phlogiston, the other (afterwards 

 called oxygen) pre-eminently a supporter of combustion be- 

 cause it contained no phlogiston. This latter gas he called 

 " dephlogisticated air." The purer the atmosphere, the less 

 phlogiston, he supposed, it contained ; its function consisting 

 in removing that element from combustible bodies. Respira- 

 tion therefore, to Priestley, was an ordinary phlogistic process, 

 the use of the lungs being to discharge phlogiston and putrid 

 effluvia taken into the system by the aliment.^ 



Meanwhile Scheele, at Koping, had discovered the same 

 gas, and termed it " empyreal air," while a third chemist, 

 Condorcet, soon wanted to change its name to " vital air." 

 The phlogiston theory, being finall}^ upset by Lavoisier, went 

 the way of other celebrated scientific delusions, such as the 

 hibernation of swallows in pools, and the scintillation theory 

 of the stars, and its overthrow necessitated a fresh appellation 

 for the new gas. This was found in " oxygen," to which it 

 had almost as little right as any of its former pseudonyms, 

 but which seems likely to cling to it as long as it continues to 

 be considered the simple element that we imagine it at present. 



We make no apology for thus describing in detail a discovery 

 which indirectly effected such enormous advantages to agricul- 

 ture. Priestley and Scheele ought to be allowed a place in 

 the foremost rank of agricultural pioneers, though it is not the 

 fashion to associate them so intimately with the farming in- 

 dustry as we do Davy, Liebig, Lawes, and Gilbert. They, 

 however, were the first two chemists to separate the ox^^gen 

 from the nitrogen of the air ; and though they did not re- 

 cognise the latter gas as an individuality, they were indirectly 

 familiar with certain of its properties when they came across 

 them in nitric acid and other compounds. In fact, as early as 

 1772, another chemist. Dr. E-utherford, whilst studying the 

 ' Gentleman'' s Mag., 1778, ]\[arch 31st. 



