An essay on combustion, with a view to a new art of dying and painting

It has been shown, in the preceding chapters, that water is essential to the reduction of metals; that it is always decomposed in that process; and that the reducing substances are oxygenated by the oxygen of the water, while the hydrogen of the latter reduces the metals.

That water is also decomposed in every instance of oxygenation, and that the oxygen of water alone oxygenates combustible bodies, will appear from the following observations.

Azote.

The first case of oxygenation, we shall consider, is that of azote, in an experiment of Dr. Priestley, which has been urged by Mr. Kirwan with great success against the Antiphlogistians.

“If the electric spark be taken in nitrous air, it will be reduced to ⅓ of its bulk, and the residuum is mere phlogisticated air, and a little acid is deposited. Now the Antiphlogistians own that nitrous air contains both pure air and phlogisticated air; since, therefore, this pure air disappears, is it not evident that it was converted into water? and since the formation of water requires the presence of inflammable air, does it not follow that the nitrous air contained this also⁠[27]?”

To this objection M. Berthollet replies, that the diminution of the nitrous gas “is owing to the combination of the mercury with the oxygene, which existed in the gas⁠[28].”

But this answer is insufficient; as it does not account for the water, and acid, that appeared: and indeed, by this experiment, the Antiphlogistians are refuted on their own principles, and the decomposition of water is incontestably proved; for as nitrous acid could not be formed without more oxygen than what existed in the nitrous air, is it not evident, that this oxygen must be derived from the water contained in the nitrous air? It is obvious then, that the water of the gas was decomposed; which seems to have been effected in the following manner.

The electric spark diminishes the attraction of the constituent principles of the water for each other; hence the azote of the gas unites with the oxygen of the water, while the hydrogen of the latter combines with the oxygen of the gas; and thus water and nitrous acid are formed.

The formation of nitrous acid in Mr. Cavendish’s noted experiment, cannot be explained on any other principle than the decomposition of water: when the electric spark is taken in a mixture of azotic gas, and vital air; the water of these airs is decomposed: the electric flame lessens the force, with which the oxygen and hydrogen of the water adhere; hence the azote seizes the oxygen of the water, and forms nitrous acid, while the hydrogen of the water unites with the oxygen of the vital air, and forms a quantity of water equal to that decomposed.

When nitrous, and vital air, are mixed; the whole mass “hisses, turns red, grows warm, and contracts in bulk,” the azote of the nitrous air attracts the oxygen of the water, and forms nitrous acid, while the hydrogen of the water unites in its nascent state with the oxygen of the vital air, and forms a quantity of water equal to that decomposed.

Hence while the azote of the nitrous air is oxygenated; the caloric is restored to its combustible state.

“But it is to be observed,” says M. Bergman, treating of this experiment, “that the decomposition of nitrous air is the effect of a double attraction; the phlogiston is attracted by the vital air, and the acid part by the water. Therefore, when the mixture is made in a phial immersed in mercury, the experiment fails⁠[29].”

Hydrogen.

The combustion of hydrogen gas with vital air is explicable only on the decomposition of the water contained in these airs: thus when flame, or a glowing body is applied to a mixture of them; the attraction of the principles of the water for each other is diminished; therefore the hydrogen of the inflammable air unites with the oxygen of the water, while the hydrogen of the latter seizes the oxygen of the vital air: thus the whole bulk of the airs, which are changed into water, disappears; and their light, and caloric, are restored to the combustible state.

Hence it appears that water is not formed during the combustion of vital, and inflammable air, in the manner the Antiphlogistians suppose.

Indeed it is obvious, that, if these airs contained no water, they could never be burned: for since they are already saturated with light, and caloric, they can have no attraction for any additional quantity of these fluids; and consequently can suffer no other change from the light, or caloric, of a glowing body, than a greater degree of expansion, and therefore could never unite.

The same reasoning applies to the combustion of all elastic fluids.

Phosphorus.

Vital air always contains a large proportion of water: when phosphorus is burned in this air, it attracts the oxygen of the water, and forms phosphoric acid, while the hydrogen of the water unites with the oxygen of the gas, and forms water, which unites with the acid.

Hence the weight of the acid formed is equal to the weights of the oxygen gas, and phosphorus, consumed; and the light and caloric, which appear during the combustion, are restored to their combustible state.

This explanation is confirmed by an observation of Mr. Bergman, who says,

“In vital air, without the aid of external heat, phosphorus is consumed very slowly, and scarce at all, unless water be present⁠[30].”

Therefore the phosphorus does not unite to the oxygen of the vital air, as M. Lavoisier supposes, but to the oxygen of the water contained in the oxygen gas.

Sulphur.

When sulphur is burned in vital air, it attracts the oxygen of the water, and forms sulphuric acid, while the hydrogen of the water attracts the oxygen of the gas, and forms a quantity of water equal to that decomposed: the light and caloric are at the same time restored to their combustible state.

The sulphur then does not unite with the oxygen of the vital air, as the Antiphlogistians imagine, but with the oxygen of the water contained in that gas.

Charcoal.

In like manner during the combustion of charcoal in vital air, the carbone attracts the oxygen of the water, and forms carbonic acid, while the hydrogen of the water unites with the oxygen of the vital air, and forms a new quantity of water equal to that decomposed.

Hence the carbone of the charcoal does not unite with the oxygen of the vital air, as M. Lavoisier supposes, but with the oxygen of the water contained in that gas.

That water is decomposed in every instance of combustion, is further proved by attending to what passes during the burning of a common fire: the carbone of the fuel combines with the oxygen of the water, and forms carbonic acid, while the hydrogen of the water unites partly with the oxygen, and partly with the azote of the atmosphere, and forms water, and the ammonia, which abounds in soot.

From these observations it is evident, that M. Lavoisier’s account of the formation of water, and acids, is erroneous, and inadequate to explain the phenomena.

The different kinds of fermentation are so many instances of the decomposition of water: in every case of them, combustible bodies are oxygenated by the oxygen of the water, while others are restored by its hydrogen to their combustible state.

Hence the azote, ammonia, and carbonic acid of fermentation, the inflammable air of marshes, mines, &c. the azotic, and hydrogen gas, ascending into the atmosphere, and there meeting the vital air discharged from the water of plants, &c. form new quantities of air, and water.

When the azote is oxygenated, it unites with the oxygen of the water contained in the air, and forms atmospheric air, and sometimes perhaps nitrous acid, the hydrogen of the water combines, at the same time, with the oxygen of the vital air, and forms a quantity of water equal to that decomposed.

But when the hydrogen is oxygenated, a quantity of water double that decomposed is regenerated; for the hydrogen of the gas unites with the oxygen of the water, while the hydrogen of the latter seizes the oxygen of the vital air: and thus a quantity of water double that decomposed is formed, and that part of it which the atmosphere cannot suspend descends in the form of rain.

When these decompositions are rapid, the phenomena of thunder and lightning appear.

This account of the renovation of our atmosphere explains why the phenomena of thunder and lightning appear sometimes with, and sometimes without rain, and also accounts for the production of the nitrous acid, which Mr. Margraaf discovered in the purest snow.

The breathing of fishes is a striking proof of the decomposition of water in respiration.

For this view of the formation of our atmosphere I am indebted to a friend well acquainted with the experiments related in this essay, and also for the application of the opinion which I venture to advance, to the respiration of animals.

The phenomena of vegetation cannot be explained on any other principle, than the decomposition of water by heat, and light, which uniting to the oxygen of the water contained in vegetables change it into streams of vital air, that serve to renovate our atmosphere: the hydrogen of the water, at the same time, contributes to form the oil and other principles of plants, and when these are decomposed by the various processes of combustion, forms a quantity of water equal to that consumed in their formation.

The changes, which nitric acid suffers by exposure to heat, or light, are explained with ease on this principle: the light unites with the oxygen of the water contained in the nitric acid, and forms vital air, while the hydrogen of the water combines with the oxygen of the acid, and forms a new quantity of water equal to that decomposed: thus the nitric is converted into the ruddy nitrous acid.

Metals.

According to the Antiphlogistians, “In every metallic solution by an acid, the metal, in order to become oxided, decomposes either the acid itself, or the water of solution, or it obtains from the atmosphere the requisite quantity of oxygene. In the second case, hydrogenous gas, in a state of greater or less purity is disengaged; and the acid remains entire without decomposition, which is proved by the quantity of alkali necessary to saturate it. In the first case, one of the principles of the acid, or the acid deprived of part of its oxygene, is disengaged, and fused in the caloric, which is separated at the same time; such are nitrous gas, and sulphurous acid gas. In the third case, neither the water nor the acid are changed; such is the solution of copper by the acetous acid.

“The muriatic acid, and the vegetable acids, which are formed of radicals, or acidifiable principles, which have more affinity with oxygene, than the metals have, are not decomposed by these metals, and the oxygene is always afforded to these last by the water or atmosphere. Hence the solutions by these acids afford only hydrogenous gas, or do not effervese at all.

“There are some cases in which the water and the acid are at the same time decomposed by the metal, as in the solution of tin in the nitric acid, according to the observation of M. De Morveau.”

“Tin is so greedy of oxygene, and requires so large a quantity for its saturation, that after having absorbed that of the nitric acid, and reduced it to the state of azote, it decomposes likewise the water, and disengages hydrogene. These two principles being separated from their first compounds, unite together, and immediately form ammoniac. Hence there is no disengagement of elastic fluid. In this case it appears, that the formation of ammoniac, in the solution of tin by the nitric acid, always takes place; for by throwing quicklime, or caustic fixed alkali, into this solution, there is always a disengagement of ammoniac⁠[31].”

It is evident, then, that this account of the oxygenation of metals, given by the Antiphlogistians, is equally complex, as their account of metallic reduction, and improbable; since every case, in which they deny the decomposition of water, and derive the oxygen from other sources, is easily, and naturally explained on that principle, as will appear from what follows.

Thus when mercury, or silver, is dissolved in nitric acid; the metal attracts the oxygen of the water, while the hydrogen of the latter unites with, and separates, more or less of the oxygen of the acid, which is thus changed into nitrous air.

The same thing happens during the solution of other metals in this acid; the only difference being the greater or less energy, and rapidity, with which they combine with the oxygen of the water.

This decomposition of water is confirmed by the solution of tin in this acid; in which the Antiphlogistians allow the decomposition of the acid, and the water too; for ammonia is formed by part of the hydrogen of the water, and azote of the acid.

In every case of metallic solution by sulphuric, and muriatic acids, whether concentrated, or diluted, water is decomposed: the metals attracting the oxygen of the water, while its hydrogen escapes in the form of inflammable air, or unites partly with the oxygen of the acid, and partly with caloric: hence the volatile sulphurous acid, and muriatic acid air, obtained, always contain some hydrogen gas, as appears from the following observation of M. Bergman.

“By means of vitriolic acid, inflammable air is obtained from zinc, and iron, as also by means of marine acid; but, from the other metals dissolved in vitriolic acid, we obtain another species of air, called vitriolic acid air; and, by the marine acid, another similar to the former, called muriatic air, but both more or less mixed with inflammable air⁠[32].”

Again, when copper is dissolved in the acetous acid; the copper attracts the oxygen of the water, while the hydrogen of the latter unites with the oxygen of the atmosphere, and forms water: hence no effervescence appears.

When alkalies dissolve metals, the latter are always oxygenated at the expence of the water, which holds the alkali in solution: thus when lead, and copper, are dissolved; the metals combine with the oxygen of the water, while its hydrogen unites to the oxygen of the atmosphere, and forms water: hence no hydrogen gas appears.

The oxygenation of metals, and other substances by heat, and air, is easily explained on the same principle: the metals, &c. unite with the oxygen of the water contained in atmospheric air, while the hydrogen of the water combines with the oxygen of the air, and forms a quantity of water equal to that decomposed.

This explanation is clearly proved by an experiment of Mr. Bergman on the regulus of manganese, which, if kept in a dry place, retains its metallic splendour; but, if exposed to moisture, is soon oxygenated, and loses its lustre⁠[33].

It is further confirmed by the authority of the distinguished Mr. Scheele, who says, that “the water contained in common atmospheric air is the chief cause of the ignition of pyrophorus,” which he proved by the following experiment.

“I made a very dry air by putting some very small pieces of quicklime into a small matrass: then I put the neck of another matrass into that of the first, so that the air of both might communicate; and I luted the crevices with wax. Two days afterwards I separated the empty matrass, and poured half an ounce of pyrophorus from my phial into it, and immediately carefully shut the aperture up: but I did not observe, that it grew in the least warm: an hour after this, I put a sponge moistened in water into the matrass, and shut it up again: a few minutes after the pyrophorus began strongly to be heated, and some pieces kindled spontaneously⁠[34].”

Many other facts might be adduced to prove, that oxygenation cannot take place without water, as the combustion of mixtures of iron filings, sulphur and water, of alkaline sulphure and water, &c. in which the water is decomposed, and the combustible bodies oxygenated by its oxygen.

It is evident then from the experiments and observations related in this essay, that water is essential to the oxygenation of combustible bodies; and that it is the only source of the oxygen that oxygenates them: it is also evident, that when one body is oxygenated, another, at least, is restored to the combustible state: hence it appears that the oxygenation of combustible bodies is never effected by a single affinity.

The Antiphlogistians treating of the precipitation of metals by each other, say,

“Since the metals cannot remain united to the acids, but in the state of oxides of a determinate degree, it is easily conceived, that by plunging into a metallic solution a metal which has a stronger affinity with oxygene than that which is dissolved, the former must deprive the latter of its oxygene, take its place in the acid, and cause the second to subside in a form more or less metallic, accordingly as it has deprived it of more or less oxygene. This is the reason of the precipitation of silver by copper, copper by iron⁠[35],” &c.

But this account of the precipitation of metals by one another cannot be admitted; for it has been proved in every instance of reduction related in this essay, that water is decomposed, and that its hydrogen is the only substance that restores bodies to their combustible state.

There is no reason then to suppose that nature deviates, in this particular case, from that uniform simplicity, which she constantly observes in all her operations.

Therefore it is obvious, that, when one metal precipitates another in a form more or less metallic; the precipitant unites with the oxygen of the water, while the hydrogen of the latter combines with, and separates, the oxygen of the precipitated metal, and thus reduces it.

The experiments made with phosphorus and metallic solutions in ether, alcohol, and water, prove the truth of this explanation; and show that when one metal precipitates another in the metallic form, it acts like a stick of phosphorus, decomposing the water.

This account of the reduction of one metal by another is supported by the opinion of Mr. Bergman, who says,

“It is well known, that the calx of copper, dissolved in vitriolic acid, is precipitated in its metallic form on the addition of iron; and that by means of a double elective attraction; for the iron dissolving in the acid would form an inflammable air by its phlogiston, were not the copper present, which takes it up⁠[36].”

The same author remarks, that a small excess of acid is necessary, and that without it no precipitation begins.

Now since water is decomposed by iron and sulphuric acid, it must be allowed, that, when iron is immersed in a solution of sulphate of copper, the water is decomposed by the iron and excess of acid, the iron attracting the oxygen of the water, while the hydrogen of the latter, unites to the oxygen of the copper, reduces it, and forms a quantity of water equal to that decomposed.

The precipitation of silver in its metallic form by iron and other metals is to be explained in the same manner: and not by a single affinity, as the Antiphlogistians imagine.

The reduction of gold, and some other metals, by solutions of sulphate of iron, and muriate of tin, is readily accounted for on the principles advanced here; for fresh made solutions of sulphate of iron, and muriate of tin, contain hydrogen, and have the power of decomposing water: the oxygen of which unites with the iron, and tin, while its hydrogen seizes the oxygen of the gold, &c. reduces it, and forms a quantity of water equal to that decomposed.

The decomposition of water is further proved by the large dilution necessary to form the arbor Dianæ, the purple precipitate of Cassius, and other instances of the reduction of metals by one another.