UNITED STATES OF AMERICA M£d v + * FOUNDED 1836 WASHINGTON, D. C. OPO 16—67244-1 INAUGURAL DISSERTATION ON THE » Chemical Properties of Atmofpheric Air SUBMITTED TO THE EXAMINATION OF THE Rev. JOHN EWING, S. T. P. Provost, THE TRUSTEES and MEDICAL PROFESSORS OF THE UNIVERSITT of PENNSYLVANIA: FOR A DEGREE OF DOCTOR OF MEDICINE, Oli'.^fG.^ / [ { TWELFTH DAY OF MAY, 1791. ! f ^ ^//S, ■z^z% IiY WILLI AM R. COZENS, OF NEW-JERSEY, member OF THE THILADELrHIA MEDICAL SOCIETY. ^- ' \~ .. .* • " Phoebe, fave novus ingreditur tua templa facerJos." PHILADELPHIA: Printed by T. DOBSON, at the Stoxe House, in Second Street. m, d cc,xci. r' T O JONATHAN ELMER, M.D. AND The Rev. ANDREW HUNTER, A. M. THIS DISSER TAT I O N IS INSCRIBED, WITH ALL DUE DEFERENCE AND RESPECT, BY THEIR MUCH OBLIGED FRIEND AND PUPIL, The AUTHOR. A 2 tar-G.;i PREFACE. TH E laws of the Univerfity of Penn- fylvania refpecting a Medical Educa- tion, have required among other things, that every candidate for a degree of Doctor of Medicine, fhall publifh a Thefis, written in the Latin or Englifh language, at his own option. Formerly the Latin language was confidered the mofr. proper medium for all fuch productions, as it was expected that almofr. every effay w7ould be read by people of different nations. But as I have not the vanity to think that this Thefis will circulate where the Englifh language is unknown, I have chofen it as a vehicle to communicate my ideas to the world, for which I have the authority of many emi- nent literary characters, which I hope will be a fufficient excufe for, and fcreen me from, the imputation of Angularity. A N INAUGURAL DISSERTATION. THE prefervation of our health, and the cure of difeafes, as well as the explanation of many chemical proceffes, being fo much influenced by an accurate knowledge of the chemical properties of the atmofphere, as alfo of inflammable and fixed air, called by M. Lavoifier hydrogen and carbonic acid gas, I confider fuffi- ciently apologies for my making the invefti- gation of them the fubject of an inaugural differtationj in which, if I differ from the moft common received opinion, I hope I fhall be excufed for purfuing that which appears to me beft eflablifhed by facts and experiments. And if I fhould not be able to add to the prefent knowledge of the fubject, fo far exhaufted by the in- tenfe labours of fo many eminent authors, I hope my well meant endeavour will not be [ 8 ] be conftrued into prefumprion. Under thefe confidcrations, I fliall proceed with theutmoft diffidence to arrange the fubject under different Sections. Sect. ill. I fhall make fome obfer- vations on the atmofphere, and its compo- nent parts. 2d. I fhall endeavour to ex- plain the nature and properties of hydro- gen gas. 3d. I fliall treat of carbonic acid gas. SECT. I. Obfervations on the'atmofphere and its com- ponent parts. *' THE atmofphere, which encircles our globe, and which we breathe, was formerly confidered to be a fimple homogeneous mafs; but by the inveftigation and expert ments of philofophers, it has been difco- vered to confift of two kinds of air, effen- tially different from each other, each of which may be eafily obtained in a feparate ftate by many artificial as well as by many natural proceffes; and when analyfed, are fuppofed [91 fuppofed by many to be fimple elementary bodies. But it is nowclearly demonstrated by chemical analyfes, that all aeriform fluids are compound bodies, compofed of a bafe more or lefs folid, united with a certain fubtle penetrating fubftance, fuppofed to be the matter of heat or elementary fire, called by M. Lavoifier, caloric: That caloric, when combined with the bafe, keeps it in a ftate of folution, and reduces it into the form of vapour or elaftic fluid, in which ftate it poffefTes the common properties of air: That thefe component parts may be de- compofed and feparated from each other by combination with other bodies; and when thus decompofed, are found to poffefs pro- perties very different from thofe they pof- fefled in a ftate of combination. The dif- ferent airs compofing the atmofphere, are pure and mephitic air, called by M. La- voifier, oxygen and azotic gas, which are always found to exift formally in it; and which are commonly combined in the pro- portion of twenty-feven parts of oxygen gas and feventy-three of azotic gas in an hundred parts of atmofpheric air. This proportion, however, is found to vary in B different L 10 ] different ftates of the atmofphere; by a knowledge of which at any given time, and the properties of thefe airs in a feparate ftate, we readily afcertain the particular properties of the atmofphere at that time, which in a great meafure influences animal health according as it is more or lefs pure, which depends on its fuperabounding ei- ther with oxygen or azotic gas. That component part of the atmof- phere, called by Mr Lavoifier oxygen gas, is proven by the experiments of philofo- phers to be compofed of a peculiar bafe combined with caloric, or the matter of heat which keeps it in its aeriform ftate, and is the only fluid capable of fupporting com- buftion and the refpiration of animals ; which is proven from its being three times as effectual as atmofpheric air in thefe pro- ceffes; that is to fay, an animal will breath three times as long in it as in common at- mofpheric air, and a body which requires four cubic inches of atmofpheric air to be entirely burnt, will require no more than one cubic inch of it for the fame purpofe; which is alfo a proof, that the oxygen gas con- [ II ] contained in the atmofphere in its common ftate, does not exceed the proportion of one- fourth of the common mafs. In the pro- cefs of combuftion the oxygen gas is de- compofed, the caloric or matter of fire be- ing feparated and diffipated, while the bafe unites and becomes fixed in the body which is burned ;-and in this manner the whole theory of combuftion is explained by thofe who deny the exiftcnce of phlogifton, or the principle of inflammability in bodies. The property and proportion of oxygen gas in the atmofphere, clearly explains why on- ly about one-fourth of a given quantity of common atmofpheric air is abforbed du- ring combuftion, and why the procefs of combuftion is effected more flowly, and with the difengagement of a lefs quantity of light and heat in atmofpheric air than in oxy- gen gas; and alfo why air, which has ferved the purpofes of combuftion and animal ref- piration, will no longer fupport animal life or maintain combuftion. This kind of air is pofTeffed of fome more of the properties of common atmofpheric air in an eminent de- gree, befides thofe which have been men-, tioned ; it exceeds, it a little in its fpecific gravity [ 12 ] gravity, the proportion between it and com- mon atmofpheric air being that of 168 to l$2. On introducing alighted candle into it, the flame not only grows larger but be- comes exceedingly bright, and when it is very pure the candle burns wiih a decrepi- tation as if it contained fome combuftible matter, at the fame time the wax or tallow waftes in a furprifing manner; the heat of the flame is in proportion to the light. If we fill a bladder of oxygen gas, and then faften to its neck a glafs tube, whofe aper- ture is drawn to a fine point, the fluid if driven out by prefling the bladder, will aug- ment the heat of the candle to fuch a de- gree, that if any fmall pieces of metal pla- ced on a bit of charcoal be held in the apex Of the flame, they will be almoft inftantly fufedy even platina may by this means be fufed ; and in a large fire there is no doubt that the effects of burning mirrors might be equalled. Oxygen, or the bafis of oxygen gas, conftitutes one of the component parts of all acid bodies, from which property it has derived its appellation; and the differ- ence obferveable in acids is fuppofed to de- pend entirely on the different kinds of mat- ter [ 13 ]. ter with which this principle is combined in forming thofe acids. Oxygen combined with metals by means of heat or any other way, deftroys their metallic quality, and Converts them into calces, which equals the weight of the metal employed, and elaftic fluid abforbed in the procefs; which fatis- factorily proves that the calcination of thefe fubftances does not depend upon the fepa- ration of a fubftance, but upon the additi- on of oxygen gas, as the weight is increa-f fed; and what further corroborates this opi- nion is, that they may be again reduced to their metallic form by feparating this bafia from them. But the moft curious and ex- traordinary property of this aerial bafis is, that it conftitutes one of the component parts of common water; for if it be united with hydrogen by combuftion, in the proportion of 85 parts of oxygen to 15 parts of hy- drogen, common water will be produced, equal in weight to the two aerial fluids employed in the procefs. This theory is farther Corroborated from obtaining hydro* gen gas bydecompofing water, by paffingit through an iron tube, heated red hot at one end, and kept cool at the other, for the pur- pofe [ H 3 pofe of applying a bladder, in which the hydrogen gas will be collected, and the oxygen gas will be abforbed by the me- tal in the infide of the tube, which will be found calcined. Many of the proceffes of nature and art alter the ftate of the at mof- phere, by encreafing or by diminifhing the proportion of oxygen gas in it. Thus (as has already been fhown) the combuftion of all inflammable bodies, and the refpiration of animals, by the abforption of the oxy- gen continually diminifhing its quantity in a given proportion of the atmofphere, gra- dually rendering it effete and unfit for farther refpiration and combuftion, as happens fre- quently in crowded gaols, hofpitals and fhips. On the contrary, other bodies, as the leaves of vegetables when acted upon by the rays of the fun, poffefs the property of decompofing water; and the hydrogen gas being abforbed by the leaves, the oxy- gen which entered into the compofition of the water is difengaged, and thereby re- news and purifies the atmofphere, and in this manner it is, that the proper proporti- on of the atmofpheric air is kept up by vegetation. Thus we fee, that one king- dom [ 15 1 dom affords the principle of exiftcnce to the other, and death to itfelf. Hence it clearly appears, that if benign Nature had not provided for the prefervation of this equilibrium, both muft foon have perifhed. Azotic gas, as obferved above, is one of the componentparts of the atmofphere, into the compofition of which it enters in the pro- portion of 73 of azotic gas to twenty-feven parts of Oxygen gas in an hundred parts of atmofpheric air. It is confidered as a compound body, as well as all the others compofed of a peculiar bafe, called by La- voifier, azote; from whence its name, com- bined with-caloric, which fufes and reduces it to its aeriform elaftic ftate, in which it exifts ready formed in the atmofphere, and is developed in proportion as the oxygen gas is abforbed or diflipated by combuftion cr animal refpiration. This was proved by an experiment of M. Lavoifier, who introdu- ced four ounces of mercury to fifty cubic inches of common air; who propofed to calcine the metal by keeping it twelve days in a heat almoft equal to that which is nc- ceflary to make it boil: after the expiration of [ 16 ] ©F the appointed time, forty five grains of the precipitate per fe were formed, and the air in the veflel was diminifhed by about one-fixth of its volume. In this ftate it in- ftantly extinguifhed candles, and killed a- nimals immerfed in it, and it did not pre- cipitate lime water; which contradicts the opinion of thofe philofophers who fup- pofe, that in the act of combuftion phlo- gifton is admitted into the air, which uni- ting with it, forms the aerial acid which renders it noxious to animals and unfit for combuftion. On diftilling the precipitate produced, about as much oxygen gas was obtained as had been loft by the common air in the calcination, and by recombining this with the noxious air left in the veflel, he reproduced a fluid nearly of the fame quality as common atmofpheric air. Hence he draws the following conclufions; firft, that five-fixths of the air we breathe is in- capable of fupporting the refpiration of a- nimals, or the combuftion of inflammable bodies. Secondly, that the furplus, or on- ly one-fixth of the volume of atmofpheri- cal air, is refpirable. Thirdly, that in the calcination of mercury this metallic fub- ftance I 17 ] ftance abforbs the falubrious parts,, leaving only the noxious portion. Fourthly, That by reuniting thofe two portions we can re- produce air fimilar to that of the atmof- phere. Many important difcoveries have lately been made refpecting the nature of this air. Its weight to that of the atmofT pheric air is as 985 to 1000; and by exr periments it is proven, that three parts of it, and (even parts of oxygen gas, expofed to the action of electric fluid, produces the nitrous acid : this difcovery clearly explains the theory of the formation of the nitrous acid in the atmofphere, and the remarka- ble fulminating properties of that Angular fluid ; when combined in the proportion of five parts of it with one part of hydrogen gas, it forms volatile alkali, as all animal and fome vegetable fubftances contain azo- tic gas ; it is in confequence of this com- bination, effected by the action of fire or putrefaction, that volatile alkali is obtained from them. Neither water, earth, nor a^ cids, have any fenfible action on this air. Thefe remarkable properties of azotic gas, are more particularly entitled to the attend tion of phyficians, as they throw great C light t 18 ] light on the medical properties of air, dif- cover the caufe of its falubrious and noxi- ous effects in certain circumftances, ex- plains the nature of animal and vegetable fubftances, the formation of volatile alkali, the production of nitrous acid, and the natural procefs of putrefaction. Various methods are employed for procuring it in a feparate ftate. The moftufual procefs con- fifts in expofing hepar fulphuris in a liquid ftate, to a given quantity of atmofpheric air under a glafs veflel; the liver by degrees abforbs the oxygen gas, Ieaviag the azotic gas behind. The procefs of combuftion, as was fhewn above, will alfo decompofe the atmofpheric air by abforbing the falu- brious part, and leaving the noxious porti- on behind. This accounts for thefuffbcati- on and death of animals which foon fol- low from burning charcoal or other com- buftible matter in a clofe room. All wri- ters, until very lately, confounded this flu- id with carbonic acid gas; but it is eafily diftinguifhed from it, by being fpecifically lighter, by having no fenfible fmell or tafte, by not changing the colour of vegetable blues, and by occafionirig no precipitation with [ 19 ] with lime water; the reverfe of all which being the properties of carbonic acid gas. SECT. II. An explanation of the nature and properties of hydrogen gas. HYDROGEN gas is a difcovery of much later date than either of the former; the properties of which it is poffeffed, are equally lingular with thofe we have alrea- dy mentioned. It is the lighteft of all the aeriform fluids, which property hath lately rendered it famous for the conftruction of air balloons, by the affiftance of which men are poffeffed of the power of traverfing, and inveftigating the fuperior regions of the at- mofphere, which before feemed denied them by nature. According to Cavendifh, by whom its greateft rarity was firft afcer- tained in the year 1766, it exceeds com- mon atmofpheric air in levity in the ratio of twelve to one, which caufes it continu- ally to tend upwards, and which explains the impurity of the atmofphere, on high mountains [ 20 ] mountains and other elevations. By itfelf it exftinguifhes flame, and kills animals, but in contact with common atmofpheric air, or oxygen gas, it is highly inflamma- ble ; which may be proved by applying a lighted candle to the furface of ftagnant waters, in which animal or vegetable fub- ftances have putrefied after agitation, from which this fluid will immediately take fire, and afford a curious appearance, which clearly explains the nature of that pheno- non called ignis fatuus, which is nothing mote than hydrogen gas, (produced in the fame manner and elevated in the atmof- phere), fet on fire by electricity which con- tinues to burn until the whole is confumed. To this caufe fome have attributed many luminous appearances in the air, fuch as weak flafnes of lightning, aurora borealis, arid the like ; but thefe appear to be more rationally accounted for from electricity alone. But the moft remarkable proper- ties of which it is pofTeffed, is, that it con- stitutes one of the component parts of com- mon water, which is proved by exploding fifteen parts of hydrogen gas by the elec- tric fpark in eighty five parts of oxygen gas, [ 21 ] gas, which it will abfbrb during combuf- tion, and common water will be produ- ced equal in weight to both gafes employ- ed. From this caufe an eminent author conjectures, that thofe fhowers which we obferve to fucceed thunder and lightning in the fummer feafon originate. He fays, " Why may not thofe fhowers which are " accompanied with thunder and lighten- " ing arife from hydrogen gas, exploded " in the fuperior regions of the atmof- " phere by electricity, and therefore chan- " ged into water?" As water is compofed of hydrogen and oxygen united, all fub- ftances which have a greater attraction with one of thefe two principles of water than they have with each other, will decompofe this fluid; hence iron and zinc are found to decompofe water, becaufe thefe bodies have a greater attraction for oxygen gas, than this has for hydrogen gas; confe- quently, that which enters into the com- pofition of water will feparate from the hy- drogen gas, and unite with thofe bodies. This fluid is produced in great quantities from the putrefaction of animal and vege- table [ 22 ] table fubftances in ftagnant water, and from various procefles both natural and artificial. SECT. III. Remarks on the nature and properties of carbonic acid gas. THE difcovery of this fluid is as anci- ent as Van Helmont, who called it gas fyl- veftris, from its being emitted in large quantities from burning charcoal. But its compofition and mode of production has been referved for the difcovery of the fa- mous Lavoifier, who has demonftrated that it is formed from charcoal, combined with oxygen gas, in the act of combuftion; from which he has called it carbonic acid, which when fufed and reduced to an elaftic aeriform ftate by combination with calo- ric, conftitutes carbonic acid gas, which is fpecifically heavier than any other per- manently elaftic fluid, being about one- third heavier than common atmofpheric air, from which it differs in many other properties, [ 23 ] properties, as well as from all other aeri- , form fluids, to wit, by poffefling the fpe- cific property of acids, fuch as turning ve- getable blues red, and being acidulous to the tafte, from which it is reckoned among the number of acid bodies. It renders cau- ftic alkalies mild, by combining with them, which clearly explains the caufe of the effervefcence produced by their union with acids. It precipitates lime diflblved in wa- ter, by decompofing the folution, by com- bining with the lime which caufes it to fall to the bottom. It kills animals, extinguifhes flame, which explains the caufe of damps found in fubterraneous caverns, and it has a confiderable antifeptic power, and will check the putrefaction of animal fubftan- ces, from which property an eminent phyfi- cian has recommended it very rationally in difeafes, of the alimentary canal, tending to putrefaction, by way of glifter. Laftly, it is readily abforbed by water, with which, it forms the mineral waters called acidulous. After clofingthis fubject, I cannot lay down my pen without embracing this fa- vourable opportunity of publicly return- in £ [ 24 ] ing my moft fincere thanks to our worthy preceptor, Doctor James Hutchinfon, pro- feflfor of Chemiftry and Materia Medica in the Univerfity of Pennsylvania, for the moft difinterefted friendfhip and innume- rable favours which I experienced from him during my ftudies in this feminary; and of acknowledging the infinite advan- tages I have received from his ingenious obfervations and accurate experiments, in acquiring the knowledge of thofe branches which he taught. FINIS. MecL. H.st. WZ mo 1711 ''IP "^pf *? <«*&!? "*,#)■> $A*&