CHAP. _9th. Whether air can be generated anew._ He repeats the experiment of dissolving iron in dilute nitrous acid, and finds that though some of the vapour be absorbed, a portion still remains uncondensible even by severe cold. On substituting dilute vitr. for nitr. acid he finds an aura which is hardly absorbed or condensed at all. Hence he doubts whether these auræ be not entitled to the appellation of air, especially as by subsequent experiment he shews that they are equally expansible with common air. In making this last experiment he exhibits the method of transferring air from one vessel to another (Tab. 5. Fig. 5.) much in the manner afterwards described by Mr. Cavendish in 1766.[45] From the inability of these auræ to support animal life (Tab. 5. Fig. 6.) he concludes finally that they are not air, though not very dissimilar p. 171. The succeeding five chapters do not seem to contain any facts or conjectures that can add to Mayow’s reputation. His Hypotheses are completely superceded by the more accurate knowledge of the present day. In his tract on quick lime p. 225 he seems to have forestalled the acidum pingue of Dr. Meyer published exactly a century afterward. It may be noted that in his treatise on the Bath waters p. 259, he describes fishes as collecting vital air from the water, and respiring like land animals. (Aereum aliquod vitale ab aquà, veluti aliàs ab aurà secretum et in cruoris massam trajiciatur.) The air bladder he considers rather as a reservoir of air to be inspired, than a receptacle for excreted air; though the latter opinion is made probable by Dr. Priestley.[46] [45] Boyle had invented an apparatus for transferring air from one receiver of an air-pump to another, but not under water. [46] See Nich. Journ. v. 3 p. 119 on the probability of fishes separating oxygen from the water they inhabit.