INSPIRATION. 



ihe expired air meafured 3362. The firft 250 cubic inches 

 confifted, in 100 parts, of 9 carbonic acid, 25 azote, 66 oxy- 

 gen ; the laif, of 12.5 carbonic acid, 5.5 azote, 82 oxygen : 

 loo parts of the whole expired air confifted of 12 carbonic 

 acid, 6.5 azote, 8 1.5 oxygen. The whole quantity of car- 

 bonic acid gas emitted in this experiment was 396.78 cubic 

 inches. Ibid. 



The refult, which fhews a greater evolution of carbonic 

 acid when oxygen is refpired, is totally adverfe to thofe ob- 

 tained by Mr. Davy, and already mentioned. We do not 

 thereiore feel authorifed in determining whether, in general, 

 an increafe in the quantity of oxygen employed augments the 

 carbonic acid evolved, or whether the proportion of the 

 latter depends on the condition of the refpiratory organs, or 

 variations in the exercife of their functions. 



It it mould be allowed, as the greateft number of invef- 

 tigations on the fubject tends to prove, that the carbonic acid 

 formed in refpiration be lefs in bulk than the oxygen gas, 

 which difappears, yet the weight of the compound is in- 

 creafed by the addition of carbon, derived from the animal 

 fyftem. Lavoifier and Seguin eftimated the weight of oxygen 

 gas confumed by a man in 24 hours, at 15661.66 grains ; 

 and that of carbonic acid produced in the fame fpace of 

 time, at 17720.89 grains ; the carbon conftituting -g-.Vth of 

 the weight of the acid formed. In the experiments of Mr. 

 D.ivy, the volume of oxygen gas that difappeared every 

 minute was 31.6 cubic inches, and that of carbonic acid pro- 

 duced 26.6 inches. But one cubic inch of oxygen gas 

 weighs 0.3474 of a grain, and therefore 31.6 cubic inches 

 will weigh 10.97784 grains : again, one cubic inch of car- 

 bonic acid weighs 0.476 of a grain, and therefore 26.6 cubic 

 inches will weigh 12.4222 grains. From thefe facts it would 

 ieem, that the proportion of carbon in the carbonic acid of 

 refpiration is much lefs than that which forms the fame acid 

 in combuition. For 100 parts of carbonic acid, formed by 

 burning the diamond, contain, according to the very accu- 

 rate refearches of Allen and Pepys (Phil. Tranf. 1807) 

 20.72 or 28.81 of carbon : and the proportion of carbon 

 in 100 parts of acid is 28.77, when it is formed from char- 

 coal and oxygen. ( Murray's Chemiftry, ed. 3. v. 2. p. 487.) 

 But there are fome points of the fubjett requiring the elu- 

 cidation of further refearches. 



Alteration in the Bull of the refpired Air. — On no point of 

 the refpiratory procefs are the recorded refults of different 

 inquiries more at variance with each other, than about the 

 queftion of the change in volume of the air, and the amount 

 of that change. At firft, it was generally believed, that 

 the refpired air undergoes fome lofs ; and this opinion main- 

 tained its ground until very lately, although experiments 

 were publimed, in which no fuch lofs was obferved. The 

 moft accurate modern refearches are much in favour of the 

 opinion, that the bulk of the atmofphere is not affected by 

 breathing ; and this view of the fubjeft is the moft generally 

 entertained in the prefent day. Some think, that, although 

 the volume of the refpired air is not affected in ordinary 

 natural breathing, it may be altered under particular cir- 

 cumftances. The determination of the queftion concerning 

 the volume of the air, is clofely connected with another re- 

 fpedting its abforption by the blood. We fhall detail the 

 facts and arguments on both fides, and point out that which 

 has the moft numerous and ftrong proofs in its favour. 



The diminution of bulk was early noticed by Boyle, who 

 eftimated it at about ,'oth of the air employed. Mayow, 

 whofe genius enabled him to anticipate fo many important 

 difcoveries of modern chemiftry, confined an animal in a 

 glafs veffel inverted over water, and, by the aid of a fy- 

 phon, brought the water on the infide of the veffel to a level 



with that on the outfide. Having then marked the height 

 of the water by pieces of paper affixed to the fide of the 

 veffel, he obferved its gradual rife as the animal continued to 

 breathe ; and then, comparing the fpace occupied by the 

 air at the commencement of the experiment, with that which 

 it poffeffed when the animal ceafed to breathe, he found that 

 it was reduced about -,!,th part of its bulk. (Tradtat. 

 Quinque, p. 104.) In the experiments of Dr. Hales, the 

 degree of diminution varied from -,-Vth to v ' th of the air 

 employed. Statical Eflays, v. 1. p. 230. v. 2. p. 320. 



Lavoifier, in the firft memoir which he publifhed upon 

 refpiration, afcertained the degree of diminution with more 

 accuracy, and ftated, that air, when rendered unfit to fup- 

 port life, was reduced -c^tli in bulk. (Mem. de l'Acad. 

 1777.) The experiments of Dr. Goodwyn afforded the 

 fame refult. 



The volume of air, taken into the lungs at a fingle in- 

 fpiration, contained, 



Phlogifticated air - - - - 80 



Dephlogifticated air ... 18 



Fixed air ..... 2 



The volume of air, expelled from the lungs at the next 

 fucceeding expiration, contained, 



Phlogifticated air ... 80 



D phlogifticated air ... 5 



Fixed air ..... 1^ 



98 



Connection of Life.. &c. p. 51. 



In the account which Lavoifier gives of the firft experi- 

 ment upon the guinea pig, he found the diminution to 

 amount to ~' r of the bulk of the air employed (Mem. de 

 l'Acad. 1780, p. 401.) ; and in the fecond fet of experi- 

 ments, the diminution was found to be -Vd p:.rt (Annales 

 de Chimie, torn. v. p. 261.); the greater abforption, in 

 thefe cafes, probably depending upon the greater purity of 

 the air employed. In the experiments performed by La- 

 voifier, in conjunction with Seguin, upon the refpiration of 

 man, though in other refpedts fo remarkable for their ac- 

 curacy, there is no mention made of this circumftance, nor 

 is it noticed by La Place, in his account of the experiments 

 in which Lavoifier was engaged, immediately previous to his 

 execution. In thefe inftances we cannot determine whether 

 Lavoifier conceived that no diminution actually took place, 

 or whether he only neglected to notice it. 



The general fact of the diminution of bulk in refpired 

 air, has been fince confirmed by Mr. Davy, though the 

 exadt degree of abforption varied fo much in his different ex- 

 periments, that it is difficult from them to fix upon a quan- 

 tity which may indicate the ordinary amount of this dimi- 

 nution. In the consideration of this queftion, as in the 

 preceding one refpedting the confumption of oxygen, and 

 the production of carbonic acid, there are two diflindt ob- 

 jedts of inquiry. We may examine the degree of diminution 

 produced in a given quantity of air, in which an animal has 

 been confined, until it is no longer fit for fupporting refpira- 

 tion ; and in the fecond place, we have to afcertain the 

 amount of the diminution which takes place in air, that has 

 only once paffed through the lungs, as is the cafe in the 

 procefs of ordinary refpiration. The firft of thefe points 

 only was examined by Lavoifier. Mr. Davy has made ex- 

 periments upon both. In air which had only once palled 

 through the lungs, he found the diminution in different 



trials 



