

CAUSES BY WHICH THE OXIGEN, &C. ] g5 



WHEN we confider the great importance of oxigen in Great import- 

 the fyftem of nature, its almoft univerfal agency and the im- ance a nd P r °d'- 

 menfe quantities which are every inftant confumed on the fur- t j on f oxigerf* 

 face of the globe, the queftion naturally arifes, from what co- in thefyftcm of 

 pious fources are we fupplied with this wonderful fubftance in na ure ' 

 a gafeous ftate? As neither animal life nor combuftion can be 

 maintained one moment without it, the quantity daily de- 

 ftroyed mud exceed all calculation. To form fome diftant 

 idea of this confumption, let us endeavour to afcertain the 

 leaft poffible quantity which muft neceflarily be decompofedin 

 a given time, in a large populous city. It is proved by expe- 

 riment, that one perfon confumes about five cubic feet of at- 

 mofpheric air in an hour, or, in other words, decompofes the 

 oxigen gas contained in that quantity. Now, if this gas is 

 taken at one fourth of the whole, it will be found that 100 

 perfons decompofe 125 cubic feet every hour, and if the popu- 

 lation of London be taken at 800,000 perfons only, the quan- 

 tity decompofed every hour, will amount to no lefs than one 

 million cubic feet. But if this quantity is deftroyed by refpi- Confumption in 

 ration alone, how much more muft be confumed by combuf-{f° ndo " I2 ?. mi1 * 



J lions of cubic 



tion in the fame fpace of time. It would indeed be difficult feet in a day. 



to afcertain with any degree of precifion, the quantity necef- 



fary for maintaining a common fire, but if the combuftion of a 



middle fized candle be equal to the confumption of one perfon 



by refpiration, it is certainly much under-rating the quantity 



if taken at four times that of the former. However, fup- 



pofing it to amount to no more, it muft follow that the oxigen 



gas decompofed by refpiration and combuftion only, in the 



City of London, amounts to the enormous quantity of five 



million cubic feet per hour. 



Soon after the difcovery of the component parts of atmo- Renovation of 

 fpheric air, Drs. Prieftley and Ingenhouz thewed by a great^^ r . by vegc * 

 number of experiments, that oxigen gas was emitted by ve- 

 getables when expofed to the rays of the fun. From this fact 

 it was immediately concluded, that the atmofphere was princi- 

 pally, if not altogether, fupplied with oxigen gas from this 

 fource. This opinion, which ftill obtains without any attempt 

 to controvert it, appears to me objectionable in feveral re(pe6ts. 

 In the firft place, it is doubtful if the fupply from this quarter 

 be at all adequate to the confumption for Dr. Prieftley, like- 

 wife founcj that vegetables during the night, emitted a gas to- 

 tally 



