■}H On phlogiston. 



No. XLIII. 



ui/i Appendix to the nvo Articles in this Volume^ (p. \.) by 

 Dr. Priestley, in a Letter to B. S. Barton, m. d. 



Dear Sir, 

 Read, Nov. O INGE fo iTiuch time has elapfed fince the 

 2j. 1798- \Jj printing of the articles which had the honour 

 of being inferted in the Tranjacliotis of your Philofophical 

 Society, I beg leave to add a few more obfervations before 

 they are publiflied. The experiments which I have made 

 fince that time have confirmed all the fa&s reported in 

 them, but not all the conc/u/ions which I then drew from 

 them. — I. Becaufe the diminution of a mixture of atmof- 

 pherical and nitrous air proceeded, in a courfe of time, 

 much farther than it does prefently after they are put to- 

 gether, I concluded that atmofpherical air contains a much 

 greater proportion of pure air than had been fuppofed, on 

 the idea that the latter part of the diminution was owing 

 to the fame caufe with the former. But I have fince 

 found that any kind of air, confined by water, the fur- 

 face of which is expofed to the common air, will in time 

 be wholly abforbcd by it, though in thofe circumftances it 

 might be fuppofed that the water in which it flood would 

 be fully faturated with air, and therefore would not be 

 difpofed to take any more, efpecially phlogifticated air, 

 which it never takes in preference to the dephlogifticated. 

 To what this unexpected circumftance is owing, I have 

 not yet fatisfied myfelf, though I have made fome progrefs 

 in the inveftigation. — Notwithftanding this, I have no 

 doubt but that part of the phlogifticated air that is found 

 after fome of the procefTes for afcertaining the purity of air, 

 is formed at the time, by the phlogifton emitted from the 

 fubflance that is ufed for this purpofe uniting with the pur- 

 er 



