VOL. LXIX.] PHILOSOPHICAL TRANSACTIONS. 533 



Mr. Scheel says, he found that the inflammable air, after being breathed some 

 time, entirely loses its inflammability ; whence he concludes, that the lungs, 

 instead of imparting some phlogiston to, imbibe it from, whatever substance it 

 can be extracted. Though all the direct experiments which show that a phlogis- 

 tic principle is continually detached from the lungs, and joins itself to the 

 common air, were wanting, still Mr. Scheel's consequence could not be drawn, 

 because the experiment is not true. With respect to my own experience I may 

 safely say, that I have always found it inflammable in every circumstance, even 

 after I had breathed it 11 times successively: and I have not only found it in- 

 flammable in the bladder, but I have fired it in the act of letting it out of my 

 mouth. In this manner a flame may be produced from the mouth, of several 

 inches in length, and 2 or more inches in breadth. 



But whence originates that sensation of levity and facility of breathing the 

 inflammable air, described above ? At present I can only have recourse to a 

 mere mechanical cause for a solution, for I do not observe in inflammable air any 

 property that seems capable of altering the lungs on a chemical principle ; nei- 

 ther have I observed any decomposition of air, or alteration of the fluids of the 

 animal. It has been observed, that inflammable air, after being breathed, comes 

 out of the lungs with the same properties it had before. It is also known, that 

 inflammable air is not sensibly absorbed by water, at least after a short time. 

 The lungs, or more properly the pulmonary vesicles, are continually moistened 

 with fluids ; but that air cannot be absorbed by them, except it be first decom- 

 posed. Nothing else therefore remains to which we can have recourse for an 

 explanation of the above-mentioned sensations, but the well-known levity of the 

 inflammable air compared with common air. And indeed the sensation I felt 

 when I breathed that air, is like that of a very light fluid which does not oppress 

 the lungs, and is hardly felt. This explanation agrees exactly with some experi- 

 ments I have made with common air rendered more light by fire. This air I have 

 found may be breathed much easier, though not for so long a time, as when it 

 is more condensed. It must be said indeed, that this is occasioned by another 

 particular cause, which has nothing to do with the case of the inflammable air, 

 and which cannot be properly examined in this place. 



After all, it still remains to be known, why inflammable air, which kills 

 animals so soon, may be breathed without any oppression, when in a small 

 quantity, viz. when it is mixed with common air ; and the following experiments, 

 which are very analogous to those related above, will show that the question is 

 not uninteresting. I introduced 350 cubic inches of common air into a bladder, 

 and after having made as strong an expiration as I could, I applied the neck of 

 the bladder to my mouth, and breathed the air it contained 40 times successively. 

 Afterwards, having taken the air out of the bladder, 1 found that it extinguished 



