S34 PHILOSOPHICAL TRANSACTIONS. [aNNO 1779. 



a light several times successively. It formed various crystals with the oil of tartar, 

 but after a very considerable time ; some of these crystals had the shape of 

 needles, others were like flowers : being tried with the nitrous air, it gave 

 II — 18, III + 18. This air therefore was very much phlogisticated, nor could 

 I possibly have breathed it longer than I did, without falling on the ground, as 

 I already felt my strength failing, and the objects appeared confused before my 

 eyes. Into 10 cubic inches of this air I introduced a small bird, which, as soon 

 as it began to breathe it, made various contortions with its body, and seemed to 

 suffer a great deal. It died in 10 minutes time ; whereas another little bird in- 

 troduced into a like quantity, that is, into 10 cubic inches of common air, lived 

 in it 52 minutes ; nor did it show any sign of uneasiness before it had been in 5 

 minutes. 



It remains to be accounted for, why the bird could breathe 5 minutes longer 

 in the air of the bladder than a man could. It will be sufficient to consider, 

 that when a man in this experiment has made the last expiration into the blad- 

 der, he is in a state of pain, and his lungs are loaden with a superfluous quantity 

 of phlogiston, which is not communicated to the air of the bladder; whereas 

 nothing of this takes place with the bird, which, besides its being in vigour, haS 

 a quantity of common air in its lungs. This seems confirmed by an experiment, 

 which admits of no doubt. Having breathed the air of the bladiler as long as I 

 could, I stopped the neck of the bladder with my finger, then breathed the 

 common air several times ; and afterwards putting the neck of the same bladder 

 to my mouth again, I breathed that very same air 4 times successively. Now 

 there is no doubt but that a bird could have breathed it much longer : the reason 

 of which diversity seems to be the following, viz. that a small bird is in want of 

 a small quantity of air for every time it breathes, whereas a man is in want of a 

 much greater quantity ; hence the air is rendered more easily noxious, and unfit 

 for respiration. From all which it may be concluded, that we are in want of a 

 certain quantity of common air necessary for respiration, and for the support of 

 life ; and that this air, after being inspired, comes out of the lungs less fit to be 

 breathed a 2d time. 



It has been observed, that the inflammable air cannot be breathed when the 

 lungs are emptied of common air as much as possible; but that it maybe 

 breathed when the lungs are in a natural state, in which state a quantity of 

 common air, equal to about 40 cubic inches, is known to exist in the lungsof 

 an adult person. This pulmonary air is not infected so far as to be incapable of 

 being breathed several times, and of supporting life. After having made a 

 natural expiration, I have with force expelled from my lungs about 30 inches of 

 air into an empty bladder ; and this pulmonary air I have generally been able to 

 breathe 8 times successively, but never longer. It is true however that I breathed 



