The Second Letter

Letter Summary: Volta details his adventures in discovering methane in various sources. To his surprise, he finds that methane is nearly everywhere he looks, although sometimes only in tiny amounts. To this point, all the research has been done at bodies of water because it’s easy to see the bubbles and capture them. However, he begins to suspect that the key ingredient in producing methane is not water, but decayed vegetation and animals. He tests this theory by digging holes in dry land near water that bubbles with methane, fills the new holes with water to look for bubbles, and finds them.

In one entertaining experiment, he pushes a stick into muddy ground to release methane and then lights the plume. He watches the flame move from hole to hole and he is dazzled by the spectacle. He finds, too, that he can jump up and down on the ground to push more methane up through the holes to get bursts of color and heat.

He begins to compare the various accounts of burning air found in scientific literature to his own experiments and finds similarities. It is his opinion, though, that he deserves naming rights based on his extensive work and proposes “Flammable Air of the Swamps”.

He is enraptued by methane. He admires its beautiful blue flame, the grace with which it burns, and the very low quantities required to create intense energy. He almost doesn’t want to label it “flammable” because it is so much more flammable than other materials that it could deserve a new name. As part of his work, he shows that methane burns when mixed with five to twelve equal volumes of air and that it burns best when mixed with eight to ten equal volumes of air. This corresponds with a flammability ratio of 7.7% to 16.7%. (A modern range, depending on factors such as pressure, is about 5% to 16%, aligning wonderfully with his original work.) For this period in history, this was extremely flammable and remarkable.

Also included in this letter are two lengthy references he sends to his friend: one considering a natural methane seep known as a “Wonder” in its province, and one by the American Benjamin Franklin. Franklin discusses stories he’s heard, but has been unable to duplicate. 

Editor's Note: If you didn't read the overview, this translation is "best effort" from someone who doesn't know Italian, let alone Italian from the 1700's. Google and other websites choke on some of the words and prose, so I've taken some liberties to bridge gaps. If you speak Italian, I've presented my typed conversion from images of the letters at the bottom. Your improved interpretations will, of course, be greatly appreciated.

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To Father Carlo Giuseppe Campi

Written 21 November 1776 from Como, Italy 

Before moving on to some other particularities that this new flammable air offers us, it is better that I give you a more accurate account of the discovery in all its details. Considering the sites which provided me with flammable air, that is, the marshes of Lake Maggiore (the bottom of which was nothing but a soft and light earth with a garbage of roots, straws, drenched herbs and so on), and seeing that the air released was flammable, yes, but very weakly, I believed at the very first that the production of this air required no less than a very large and very abundant mass of pure sludge, that is, of vegetation that was broken down and reduced to earth. Also, I will tell you that my ideas soon turned towards peat, pondering its quality of burning with a blue flame. I had the hope to conveniently collect flammable air along the shores of a lake not far from the city, but consider that it does not have any reeds, nor a very muddy bottom of water, and only happens to be covered with pulp or at most green weeds. It would have been a very natural thing that I should not let myself do the experiment there. However, walking close to these shores and probing with a cane almost everywhere in the bottom of the water, I saw that where it was not too hard or purely gravel or stony, bubbles rose to the surface of the water. If I had judged the area in advance, I would have said, to say the least, the air is phlogisticated, and pointed to the unsuitability of the sources, for instance, when I flushed it from a bed that seemed pure earth or fine sand. But the fact is, that, put to the test, the air samples were flammable, except one, in which I found it plogisticated because it immediately extinguished a candle dipped into it.

After such an adventurous and unexpected success, imagine if I left untouched the spring, or the river, the pool, or the stream, the ditch, or a puddle I happened to walk by? Yes, for the space of many days, I did nothing but go probing and stirring every bed of water at its shoreline,  and brough back home with me a pocket full of small vials full of new air samples to test. In short, there was no water-covered ground from which I could not somehow get air that was flammable, except that I often found it diluted with a portion of fixed air; and no ground refused to produce it for me, unless it was either hard or gravelly. 

I said I had collected air from pure grounds free from decomposing materials. However, their water surfaces were completely coated with a simple layer of slime or mire, which at first you would say were too thin to be considered. It was not without wonder to have found there flammable air like any other. I must not, however, neglect to add that the air that emerged from there is far less abundant than that which develops from the bed of certain waters composed of putrid herbs piled up and tangled with lotus plants. Some ditches and certain dead, corrupt, and stinking waters teem with air bubbles at the slightest disturbance of their bottoms; contrary to expectations, many of these bubbles even appear spontaneously and it is not uncommon to see them covering the surface, and they are expected to be afloat and last for a long time without bursting. It is therefore not unlikely that from vegetation macerated and corrupted in the water, and perhaps even from animals (because in the sludge of some abundant ponds of flammable air I have been able to see the remains of several insects) and not from the pure earth or other fossil substance, less then by water, our inflammable air has its origin. In fact, by examining more carefully, I found that even in those beds which seemed to be made of nothing but earth, yet sometimes a little or sometimes a lot of air was released from them. There was, in these cases, if nothing else, a moss or some vegetation, or a greenish and mucellaginous mold that covered some stone. And where these conditions were not met either, and the gravel, and the pebbles were clear of vegetation and smooth, and the water ran clear, not even a little bubble was to be hoped for; it never occurred to me that I could get a bubble from the mud of the public streets.

After having tested the dormant land under the water, my imagination ran quickly (as I already told you in my previous letter that I had in mind to test the shoreline of the source you observed) to examine the land close to the water, but not wet. I therefore chose a marshy ground, left almost dry by the retreat of our lake; and I set about testing in two ways. The first to dig some wells in the mire (others were formed by deep footprints) and fill them with water. By probing them with a stick, I flushed the air, diligently collected it, and the samples did not fail to catch fire. The other method, that offered me a more beautiful and more graceful spectacle, was to forcefully push a stick in the ground where it was softer and blackish, or covered in spoiled vegetation, and then pull the stick out and present a lit candle to the hole. It was beautiful to see a blue flame immediately ignited, with one side of it shooting upwards into the air and the other side plunging and grazing the bottom of the hole. Then quickly digging many adjoining wells, my eyes did not know where to look as the flame flowed from one to the other. Now to this, and now to that set on fire, and now to burn and shine all at once and then to ignite in a vigorous burst if I  trampled the ground with my feet to release more air.

What do you think of this, my friend? The phenomenon, which with so much emphasis is described to us, of some land on which a flame arouses and passes, lapping it all just by throwing a lit match into it1, I can show it to you whenever you like: nothing more is required than plowing the earth or riddling it with holes. I have read of some pond which offers the same spectacle of a flame, but it unfolds over the whole surface of the water2; and I wanted to recreate that for myself. I caused the bottom of a ditch of the most sordid and swampy ground to be tilled and submerged, so as to give birth to a great number of gurglings; and here at the approach of a burning candle to the water, I ignited a large lapping flame. The significant difference in my experiment, relative to others above ground, is the continuous action to disturb the bottom to release its air, which is not required in all those sites of which results such as these are read. In spite of this non-trivial circumstance, I do not doubt the identity of the principle in all the cases mentioned in these references. I feel confident of its identity with respect to the so-called Fuochi Fires. Many circumstances, to tell the truth, could make me believe that in the end nothing else but flammable air is squeezed from the marshy ground, since it usually is found around the marshes. But if such is their nature, how will we explain their lighting, since we know of no other means of igniting the flammable air than that of putting a flame near it?

Since now everything and every semblance of a thing is given a name, and many of them in particular have been manufactured for the different species of air, I am reminded to ask you, if we could call this freshly found air “Flammable air native to the Swamps”. Besides that it, in fact, originates from it, I would have the right to label this form given the remarkable color for which it distinguishes itself from other flammable and natural airs. If for no other reason than the color of the flame, elegantly blue, and the slowness with which it very smoothly advances, lapping and swaying, it differs completely from that which is generated with metallic solutions in acids and some little from that which is obtained from substances or vegetation or animals by distillation. I have never had occasion to test flammable air native to coal mines or rock salts; however, I also have no doubt that our own air may differ from these.

I have already told you that it burns much more slowly than the others, and that its bursts are not beholden to those of the others; I almost told you that it just barely deserves to be called merely flammable. You will never expect it from me, and beyond any doubt it will seem paradoxical that I want to sing and dance in virtue of its extreme abundance relative to all the others. Yet this is so and not otherwise. Yes, sir, there is no air more flammable than the native air of the swamps. This in the first place can be deduced from the overwhelming number of small blowouts that results. But another more certain and decisive clue to me seems to be that of communicating the virtue of being inflamed to the common air with which it is mixed, which is to our great advantage relative to the other ignitable airs. The strongest of these, obtained with an iron filing solution in vitriolic acid, begins to crackle with a loud roar and noise when it is intermixed with a common air volume double its own; that of the swamps (or collected in any case from vegetation) ignites and bursts with maximum energy if to one measure of it are added eight to ten measures of common air; intermingling it with only five or six measures, however, does not produce the maximum flash and rumble, but it does flash with various successive and slight flames. Finally, mixing up to twelve measures of common air with one of the swamps, the whole mixture has not failed to go up in flames. 

Now it is understood why this air burns so lazily in the vessels and requires that these be of wide mouth. No, it is not its lack of flammability. On the contrary, it is the excess and disproportionate amount of it, since in order to flare up vigorously it would have to be extended and tempered with a lot of common air. That if, whatever the proportion of the two airs mixed together (that is, the common and the flammable native airs) the explosion never reaches that level to which the other flammable airs touch, in my opinion it must still be concluded that it is a different air endowed with a lot of virtue to ignite and to have a lot of strength while it is burning. I conceive that this diversity will arise not so much from the dose of phlogiston as from the different ways in which it can combine with these airs, and above all from the nature of the base with which it is coupled, with greater or lesser affinity and etc.

I will not delay in writing, in continuation of the previous two, one or more other letters, in which I will mention some of my ideas on the flammability of airs in general.

Yours,

Alessandro Volta

References mentioned in his letters:

1 The description of a similar phenomenon is found in Volume I of the Commentaries of the Accedemia of Bologna, where it is said that the famous Mr. Galeazzi observed and examined in 1719 certain neighboring lands of Barigazia, where [unclear] lives from time to time. Another more recent and more purposeful description of the so-called “Ardent Fountain of the Dauphiné” is found recorded in the Journal of the Abbot Rozier, (Observations on Physics, 6th August 1775). 

“In sum, says the anonymous author on p. 126, the whole area of the ground from which the flame comes out, and in particular that which is below and on the sides, is a black Schist and flaked in sheets or sheets which have the appearance of Slate. Above many of these sheets, the shape of various shells is impressed, but mainly that of the Came. 

While I was collecting some essays, my guide had prepared a couple of eggs and, no longer able to bear the desire to show me the show, he lit a match and threw it on the ground. Instantly, I saw that whole stretch of land covered with a light flame which seemed to sway in that way that the flame of the spirit of wine sways, and above it my leader cooked a diabolical omelette. I was free from the curiosity to taste it and, in fact, little more than tasting it would have provided me in any case the unbearable flavor of sulfur. For what belongs to the flame, I could not judge neither of the color nor of the height, because the sun that shone clear on that day prevented me from seeing both, as would have been seen were the air dark and the sky overcast. I judged that the color had to be bluish; and the guide told me that such color appeared in night time; but being in the sun, I saw only a red flame. I was left with doubt, and it made me very sad that I didn't have the Thermometer with me; I would have liked to have known to what level the heat of the earth was rising at different depths, or at least below the surface. To make up for the lack of a suitable instrument, I pierced the earth in a place very close to the flame and I dipped a finger into it, but I felt no greater heat than that of the other earth. A few minutes later I was forced to withdraw my finger, because the flame came down to fill the hole from above; and in that precise way that an extinguished yet smoking candle is relit by directing its smoke towards another burning candle, so the flame came to fill the hole I made and to cover all around it.”

Such is the alleged Fiery Fountain of the Dauphiné, which is celebrated for one of the seven wonders of that Province.

2 Here is one example of many which could be produced. I have chosen it because it is very recent and because it is supported by the authority of that great and famous man, Mr. Benjamin Franklin.

A Letter from Dr. Franklin.

Craven Street, April 10, 1774.

Dear Sir,

In compliance with your request, I have endeavoured to recollect the circumstances of the American experiments I formerly mentioned to you, of raising a flame on the surface of some waters there.

When I passed through New Jersey in 1764, I heard it several times mentioned, that by applying a lighted candle near the surface of some of their rivers, a sudden flame would catch and spread on the water, continuing to burn for near half a minute. But the accounts I received were so imperfect that I could form no guess at the cause of such an effect, and rather doubted the truth of it. I had no opportunity of seeing the experiment; but calling to see a friend who happened to be just returned home from making it himself, I learned from him the manner of it; which was to choose a shallow place, where the bottom could be reached by a walking-stick, and was muddy; the mud was first to be stirred with the stick, and when a number of small bubbles began to arise from it, the candle was applied. The flame was so sudden and so strong, that it catched his ruffle and spoiled it, as I saw.

New-Jersey having many pine-trees in different parts of it, I then imagined that something like a volatile oil of turpentine might be mixed with the waters from a pine-swamp, but this supposition did not quite satisfy me. I mentioned the fact to some philosophical friends on my return to England, but it was not much attended to. I suppose I was thought a little too credulous.

In 1765, the Reverend Dr. Chandler received a letter from Dr. Finley, President of the College in that province, relating the same experiment. It was read at the Royal Society, Nov. 21, of that year, but not printed in the Transactions; perhaps because it was thought too strange to be true, and some ridicule might be apprehended if any member should attempt to repeat it in order to ascertain or refute it. The following is a copy of that account.

"A worthy gentleman, who lives at a few miles distance, informed me that in a certain small cove of a mill-pond, near his house, he was surprized to see the surface of the water blaze like inflamed spirits. I soon after went to the place, and made the experiment with the same success. The bottom of the creek was muddy, and when stirred up, so as to cause a considerable curl on the surface, and a lighted candle held within two or three inches of it, the whole surface was in a blaze, as instantly as the vapour of warm inflammable spirits, and continued, when strongly agitated, for the space of several seconds. It was at first imagined to be peculiar to that place; but upon trial it was soon found that such a bottom in other places exhibited the same phenomenon. The discovery was accidentally made by one belonging to the mill."

I have tried the experiment twice here in England, but without success. The first was in a slow running water with a muddy bottom. The second in a stagnant water at the bottom of a deep ditch. Being some time employed in stirring this water, I ascribed an intermitting fever, which seized me a few days after, to my breathing too much of that foul air which I stirred up from the bottom, and which I could not avoid while I stooped in endeavouring to kindle it.—The discoveries you have lately made of the manner in which inflammable air is in some cases produced, may throw light on this experiment, and explain its succeeding in some cases, and not in others. With the highest esteem and respect,

I am, Dear Sir,

Your most obedient humble servant,

1. Franklin.

…

It also is worthy, because it so much like our case, to consider the passage given by Chiariss. Sig. Dr. Gio Luigi Targioni, which is registered in Volume I, page 37, of article VI of his beautiful Physical-Medical Brochure Collection. Here are the words:

“Another analysis made by Mr. Zuccagni himself of mineral water at a place called Bagnolino, not far from Florence, will show that not all mineral waters contain fixed air and that, in some springs, flammable air is observed.”

Original Italian

Lettera seconda

Al medesimo

Como, 21 Novembre, 1776

Prima di passare ad alcune altre particolarità che ci offre cotesta nuova aria infiammabile, conviene che vi renda un conto più esatto della scoperta in tutta la sua estensione. Considerando i siti, i quali fornito m' aveano aria infiammabile, cioè le Paludi del Lago Maggiore, il cui fondo altro non era che una terra soffice e leggiera, ossia un pacciume di radici, cannucce, nicchi, erbette infradiciate ec.; e vedendo l'aria sprigionatane infiammabile sì, ma debolissimamente, credetti in prima in prima, che all produzione di tale aria non si richiedesse meno di un cosiffatto ammasso larghissimo e prodondissimo di puro fradiciume, ossia di vegetabili scompposti e ridotti in terra. Dirovvi eziandio, che le mie idee si volsero tosto alla Torba, attesa la qualità sua di infuocarsi, e di ardere con una fiamma turchina. Pertanto appena appena io avrei sperato di raccogliere aria infiammabile lungo le sponde di questo mio Lago non guari discoste dalla Città, ove non avvi alcun canneto, nè fondo d'acqua assai fangoso, ma avviene soltanto di trovarsene taluno coperto di poltiglia, o al più di erbacce verdi: con tutto ciò era cosa assai naturale, che io non lasciassi di fare sopr' essi pure l'esperimento. Prima adunque passeggiando rasente queste rive, e colla canna tentando, e quasi interrogando per ogni dove il fondo dell' acqua vidi, che ovunque esso non era troppo sodo, o puramente ghiaioso, e sassoso, montava al pelo dell' acqua ove un maggiore ove un minor numero di gorgogli d'aria. Giudicandone anticpatamente l'avrei riputata, a dir molto, flogisticata, e talora punto o poco diversa la commune, quando cioè io la snidava da un letto che sembrava terra pura o sabbia fina. Ma fatto sta, che messa alle prove riuscì in ogni caso infiammabile, tranne un solo, in cui la trovai flogisticata, perchè spense una candelletta al primo immergervela dentro.

Dopo un cosiffatto non meno avventuroso che inatteso successo, immaginate se io lasciai intatto fonte o fiume, polla o rigagnolo, fosso o pozzanghera in cui m'avvenissi. Sì, per lo spazio di ben molti giorni, altro non ho fatto che andare tastando, e rimestando ogni letto d'acqua del contorno, colla tasca piena di guastadette che mi riportava a casa colme di novella aria. A dir corto, non v' ebbe fondo da cui io potessi in qualche modo ottener aria, che questa non sia slata infiammabile, se non che sovente l'ho trovata confusa con qualche porzione d'aria fissa; e niuno niuno ha rifiutato di darmene, salvo che fosse o affatto duro o ghiaioso. Ho detto d'aver raccolto aria da que' fondi pure che coperti non sono d'alcun fracidume, ma veggonsi, per cosi dire, spalmati d'una semplice falda di melma o belletta, che a prima giunta direste terra pura o anzi arena sottile; e di avere non senza maraviglia trovata tal' aria infiammabile al par dell' altra. Non debbo però tralasciare di soggiugnere, che l'aria sbucata di là è di gran lunga meno copiosa di quella che si sviluppa dal letto di certe acque composto di erbe putride ammucchiate e confuse con un loto leggiere e consenziente. Alcuni fossati e certe acque morte, corrotte e puzzolenti brulicano tutte di gallozzole d'aria, solo che dolcemente se ne smuova il fondo; anzi molte di cotali bolle veggonsi comparire qua e là spontaneamente, e non di rado avviene di vederne coperta tutta quant' è la superficie, attesochè portatesi a galla durano ivi assai tempo senza crepare. Egli è adunque non poco verisimile che da' vegetabili macerati e corrotti nell' acqua, e fors' anche dagli animali, perchè nella fanghiglia d'alcuni stagni abbondanti d'aria mi sono venuti sott' occhio gli avanzi di più insetti, e non dalla pura terra o da altra fossile fostanza, motlo meno poi dall' acqua, abbia la sua origine questa nostr' aria infiammabile. Diffatti esaminando le cose più attentamente, rinvenni che eziandio in que' letti, i quali sembravano fatti di null' altro che di terra, eppure sprigionavasi da essi o poca o molt' aria, vi avea, se non altro, un musco o qual si soffe erba, o muffa verdiccia e mucellaginosa che copriva alcuni fassi: ed ove non inctrontravasi neppur questa, e la ghiaia, e i ciottoli trasparivano mondi e lisci, e l'acquea se ne scorrea limpida, una gallozzola, che è pur poco, non era da sperarsi; anzi non m'avvenne mai di poterne ottenere una nè meno dal fango delle pubbliche vie. 

Dopo aver saggiata la terra che dorme, dirò così, sotto l'acque, mi è tosto corso per la fantasia (come già vi dissi che aveva in animo di fare ne' contorni della sorgente da voi osservata) di esaminare la terra vicine all' acqua, ma non bagnata. Ho scelto pertanto un terreno paludoso, lasciato quasi in secco pel ritiramento del nostro Lago; e mi sono accinto a far le prove in due modi. Il primo su di scavare a bello studio alcune pozzettine nella mota, altre eran belle e formate dalle orme stampate profondamente, e ricolmatele d'acqua, col frugare alla maniera usata per mezzo del bastone, snidai l'aria, diligentemente la raccolsi, e non mancò alla prova d'infiammarsi. L' altro che mi offrì uno spettacolo piu bello e più grazioso, su di spignere a viva forza il bastone nel terreno ov' era meno sodo e più nericcio, o d'erbe guaste ricoperto, e trattolo fuori, presentar tosto al pertugio una candeletta accesa. Era pur bello il vedere nascer subitamente una fiamma azzurrina, e una perte d'essa lanciarsi in alto, l'altra immergersi e andar radendo il fondo. Scavando poi in fretta molte pozzette contigue, gli occhi non sapean saziarsi in mirare la fiamma scorrere da una all' altra, ed ora a questa, ora a quella appiccar fuoco, ed ora arder tutte e brillare a un tempo e a un tratto, in ispezie, se io co' piedi o m' aggravava sul terreno o lo calpestava perche ne schizzasse più aria. 

Che ne dite, Amico? Il fenomeno, che con tanta enfasi ci viene descritto, di qualche terreno sul quale destasi e trascorre, lambendolo tutto, una fiamma, al solo gettarvi un solfanello acceso1, io posso mostrarvelo ognor che v' aggrada: per cio nulla piu si richiede che foracchiare o solcare la terra. Ho letto di alcuno stagno, che offre il medesimo spettacolo d'una fiamma che si spiega su tutta la superficie dell' acqua2; ed io ho voluto pure imitarlo. La diversità grande sta tutta in ciò, che così in questo sperimento, come nell' altro fatto sopra la terra, è di mesteri un' azione continuata di smuover il fondo per isnidare l'aria, il che non richiedesi in tutti que' siti di cui si legge la descrizione. Malgrado cosiffatta non leggiere circostanza io non dubito dell' identita del principio in tutti i casi accennati. Così accertar mi potessi dell' identità rispetto a' così detti Fuochi fatui. Molte circostanze, a dir vero, potrebbero farmi credere, che altro alla fine non sieno se non se aria infiammabile spremuta dal terreno paludoso, giacchè appunto sogliono intorno alle paludi farsi vedere. Ma se tale é la loro natura, come spiegheremo il loro accendersi, poiché altro mezzo non conosciamo d'allumare l'aria infiammabile, che quello di accostarvi una fiamma?

Giacchè ora si dà un nome ad ogni cosa, e ad ogni apparenza di cosa, e tanti segnatamente se ne sono fabbricati per le diverse specie d'aria, mi sovviene di chiedervi, se potremmo chiamare questa di fresco trovata Aria infiammabile nativa delle Paludi. Oltrechè essa ne è infatti originaria, io mi riputerei in diritto di contrassegnarla per tal foggia, attese le rimarchevoli apparenze, per cui si distingue dalle altre arie infiammabil i e fattizie e naturali. Se non altro pel colore della fiamma elegantemente azzuro, e per la lentezza con cui s'avanza cheta cheta, lambendo e ondeggiando, differisce confiderevolmente da quella che viene generata colle soluzioni metalliche negli acidi, e alcun poco da quella pure che cavasi dalle fostanze o vegetabili o animali per distillazione. Non ho avuto mai occasione di metter a cimento l'aria infiammabile native delle miniere di carbon fossile, o di sal gemma; pure non dubito punto, che eziandio da queste differir possa la nostra.

Già vi ho detto, che essa arde assai più posatamente delle altre, e che gli scoppi suoi non sono per conto alcuno da mettersi a petto di que' delle altre; per poco io non vi dissi che appena appena merita d'essere chiamata infiammabile. Senza fallo adunque voi non v' aspetterete mai, e fuor d'ogni dubbio vi sembrerà paradosso, ch' io mi voglia mettere sul mostrarvela di questa virtù a dovizia fornita e straricca sopra tutte le altre. Eppure la cosa sta così e non altrimenti. Sì, Signore, non v' é aria piú infiammabile dell' aria nativa delle paludi. Ció in primo luogo puó dedursi dal numero stragrande di piccole scoppiature che se ne ottiene. Ma un altro piu certo e decisivo indizio a me pare esser quello di comunicare la virtu d'infiammarsi all' aria comune con cui venga mescolata, nel che la nostra vantaggia di gran lunga le altra arie accendibili. Ma un altro più certo e decisivo indizio a me pare esser quello di comunicare la virtù d'infiammarsi all' aria comune con cui venga mescolata, nel che la nostra vantaggia di gran lunga le altra arie accendibili. La più forte di queste, ottenuta colla soluzione di limatura di ferro nell' acido vitriolico, giugne a scoppiettare col maffimo strepito e romore ove venga frammischiata con un volume d'aria comune doppio del suo; quella delle paludi o cavata comunque da' vegetabili all' incontro s'infiamma e scoppia col massimo vantaggio, se ad una misure di essa aggiungansene le otto, e le dieci di comune; frammischiandone soltanto le cinque o le sei non iscoppia tuttavia col massimo lampo e rimbombo; ma si va balenando con vari successivi e lievi infiammementi: finalmente mescolando infino a dodici misure d'aria comune con una della paludi, non ha mancato di andar in fiamma tutta la massa.

Ora s'intende perchè quest' aria arda tanto pigramente ne' vasi, e richieggasi che questi sieno di ampia bocca. No, non è già mancanza d'infiammabilità, vuol anzi dirsi eccesso e dismisura, in quanto che per fiammeggiare vivamente debbe genir dianzi allungata e temperata con dimolta aria comune. Che se, qualunque sia la proporzione delle due arie fra di loro mescolate, cioè della comune e della infiammabile nativa, lo scoppio non giugne mai a quel segno cui toccano le altre arie infiammabili fattizie, altro, secondo me, non si dee conchiudere, se non che diversa cosa è l'esser un' aria dotata di molta virtù d' infiammarsi, e l'avere molta forza nel mentre che s'infiamma. Io concepisco che tale diversità nascer possa non tanto dalla dose del flogisto quanto da' diversi modi in cui esso può combinarsi con queste arie, e soprattutto dalla natura della base con cui è accoppiato, dalla maggiore o minore affinità ec.

Non tarderò guari a scrivervi, in continuazione delle due precedenti, una o più altre lettere, nelle quali vi accennerò alcune mie idee sull' infiammabilità dell arie in generale.

Amatemi, ch'io sono ec.

1 La descrizione di un somigliante fenomeno leggesi nel tomo I. de' Commentari dell' Accedemia di Bologna, ove vien detto che il celebre Sig. Galeazzi osservo ed esamino nel 1719 certo terreno vicine di Barigazia, do cui sorgano volta a volta vive namme. Un' altra descrizione piu recente e piu al proposito nostro, della cosi detta Fontana ardente del Delfinato, trovasi registrata nel Giornale dell' Abata Rozier (Observations sur la Physique & c. tome sixieme Aoust 1775.) In somma, dice l'Autore Anonimo alla pag. 126, tutto il contorno del terreno da cui esce la fiamma, e segnatamente quello che gli sta piu sotto e a' fianchi, si e uno Schifto nero e sfaldato in lamine o sfoglie per cui veste l'apparenza d' Ardesia. Sopra molte di queste sfoglie vedesi impressa la forma di varie conchiglie, ma principalmente quella delle Came. 

Mentre io ne raccoglieva alcuni saggi, la mia guida avea allestito un paio d'uova, e non potendo piu reggere al desiderio di farmi vedere lo spettacolo, accese un solfanello e gettollo sul terreno onde dovea sortir il fuoco. All' istante io vidi tutto quel tratto di terra coperto d'una vampa leggiera, e che sembrava ondeggiare a quel modo appunto che fa la fiamma dello spirito di vino acceso, e sopr' essa il mio condottiere fe cuocere una diabolica frittata. Mi lasciai prendere non già dalla gola, ma sibbene dalla curiosità di gustarne, e in fatti poco più oltre che assaggiarla mi avrebbe permesso in ogni caso il sapore insopportabile di solfo che ne veniva. Per cio che spetta alla fiamma, io non potei giudicare ne del colore ne dell' altezza, perche il sole che risplendeva chiaro in quel giorno mi tolse di vedere e l'uno e l'altra, come veggonsi allorche l'aria e oscure e il cielo coperto. Io giudicai che il colore dovea essere turchiniccio; e la guida mi disse che tale diffatti compariva in tempo di notte; ma stando al sole, io non vedeva, che una fiamma rossa. Mi restava un dubbio, e che faceami dolere assai di non aver meco il Termometro; avrei pur voluto sapere a che segno montava il calore della terra a qualche profondita, o almeno sotto la superficie. Per supplire alla mancanza d'un acconcio strumento forai la terra in un luogo assai assai vicino alla fiamma, vi immersi un dito, ma non sentii calor maggiore di quello dell' altra terra. Pochi minuti dopo fui obbligato a trarne il dito, perche la fiamma venne a riempire il pertugio per di sopra; e in quel modo appunto che una candela spenta e tuttavia fumante si raccende accostandola, e dirigendone il fumo verso un' altra candela che arde, cosi venne la fiamma a riempire il foro da me fatto, ed a coprirne tutto il dintorno.

Tale e la pretesa Fontana ardente del Delfinato, e che viene celebrata per una delle sette maraviglie di quella Provincia.

2 Eccone un esempio preposto a molti altri, che se ne potrebbero addurre e perchè assai recente, e perchè appoggiato all' autorità d'un uomo cotanto grande e famoso, quanto è, e sarà mai sempre il Sig. Beniamino Franklin.

Al Sig. Giuseppe Priestley.

Craven Street, li 10 Aprile, 1774

Signore,

Per condescendere alle vostre richieste, ho posto ogni opera e sollecitudine in raccogliere le circostanze deglie esperimenti tentati in America, de' quali vi ho già fatta menzione, cioè dell' alzarsi una fiamme sulla superficie di alcune acque di colà. Allorchè io passai pella Nuove Jersey, l'anno 1764, udii più d'una fiata ricordare, che appressando una candela accesa al pelo di alcuni di que' fiumi, si apprendea all' acqua e spiegavasi su di essa una subita vampa, che durava a brillare per lo spazio d'intorno a mezzo minuto. Ma le descrizioni che me ne vennero fatte erano imperfette a segno, che non potettie formare veruna congetture sulla cagione di cotale effetto, ed anzi inchinai a dubitar forte della verità di esse.

[FRANKLIN’S LETTER OMMITTED DUE TO FINDING THE ORIGINAL ENGLISH VERSION]

Merita pure, perchè troppo al caso nostro, d'aver quì luogo un passo del Chiaris. Sig. Dr. Gio Luigi Targioni, registrato nel Vol. I. pag. 37 dell' articolo VI della sua bella Raccolta d'Opuscoli Fisico-Medici. Eccone le parole:

Un' altra analisi fatta dall' istesso Sig. Dr. Zuccagni di altr' acqua minerale di un luogo detto Bagnolino, poco distante da Firenze, dimostrerà, che non tutte le acque minerali contengono aria fissa, e che in alcune sorgenti si osserva dell' aria infiammabile.