Pyrolysis

“ The causes of spontaneous combustion may be referred to chemical decomposition, and the change of quiescent into distributable heat. We remarked, that a mixture of chlorate of potassa and sugar is inflamed, when brought in contact with sulphuric acid; that, in the slaking of quicklime, the heat is sufficient to inflame oils; that pyrites by decomposition very frequently sets fire to combustible bodies; that oil of turpentine is inflamed by nitric acid; that pyrophorus, when exposed to the air, takes fire, and also phosphorus by slight friction ”

“ By the ordinary process we obtain sundry volatile [92] products, among which are pyroacetic acid and carburetted hydrogen gas.
When wood is carbonized in the usual manner, it yields from 16 to 17 parts of charcoal in the hundred; but when the operation is conducted in close vessels, the product is 28 per cent. a saving of eleven or twelve per cent. By this difference in the quantity, it appears that eleven or twelve per cent. is burnt in the common process. ”

“ By the combustion of bodies, substances are generated that are either gaseous or solid, whence arises the variety of products. Of aëriform fluids, some are coloured, as nitrous acid vapour, (nitrous gas and oxygen) , chlorine, and the protoxide and deutoxide of chlorine. The first is red, the rest yellowish-green, or yellowish. Some relight a taper, provided the wick remain ignited, as oxygen gas, protoxide of azote, and the oxides of chlorine. Others produce white vapours in the air, as muriatic acid, fluoboric, fluosilicic, and hydriodic. ”

“ The point to be attended to is, to bring the wood to a complete state of ignition, and consequently to disengage all the volatile or fluid parts. When the gas (carburetted hydrogen) ceases to appear, it is a criterion that the operation is finished. This gas, it is to be recollected, will come over even after the whole of the wood is completely ignited. The first volatile product is the pyroacetic acid. Some saturate the acid liquor with chalk, and decompose the acetate of lime with sulphate of soda, and separate the acetic acid from the acetate of soda by distillation with sulphuric acid. ”

“ If ammoniacal gas be formed, the hydrogen must proceed from decomposed water, and the azote from the nitric acid. Prussine, cyanogen, or carburet of nitrogen, the radical of prussic acid, may also be generated by the union of carbon and nitrogen or azote, in the same manner. We know that cyanogen may exist in the form of gas; but as it is inflammable, burning with a bluish flame mixed with purple, we may infer, nevertheless, that, if generated, it must undergo decomposition by the process of combustion. ”

“ Thus, at the first application of the fire, whenever the heat produced exceeds the temperature of boiling water, part of the oxygen and hydrogen unite to form water; soon after the rest of the hydrogen, and part of the charcoal, combine into oil; and, lastly, when the fire is pushed to the red heat, the oil and water, which had been formed in the early part of the process, become again decomposed, the oxygen and charcoal unite to form carbonic acid, a large quantity of hydrogen gas is set free, and nothing but charcoal remains in the retort. ”

“ A few examples will be sufficient. By the combustion [xxv] of metals, iron for instance, we obtain a fixed product, and in the present case an oxide of iron; by the combustion of antimony and arsenic, the antimonic and arsenic acids; by the combustion of charcoal, we have carbonic acid gas, a gaseous product; by the combustion of potassium or sodium, we obtain a fixed alkali, depending however on the quantity of oxygen; by the combustion of sulphur, phosphorus, &c. acids; and when metals are burnt in chlorine gas, chlorides are produced. ”

“ You see it is not combustible, nor does it support combustion. Neither, as we know, does it dissolve much in water, because we collect it over water very easily. Then, you know that it has an effect, and becomes white in contact with lime-water; and when it does become white in that way, it becomes one of the constituents to make carbonate of lime or limestone.
The next thing I must shew you is, that it really does dissolve a little in water, and therefore that it is unlike oxygen and hydrogen in that respect I have here an apparatus by which we can produce this solution. ”

“ M. Proust considers, that nitrite of potassa, prussiate of potassa, charcoal, sulphuretted hydrogen gas, carburetted hydrogen gas, nitrous gas, and carbonic oxide gas may be generated or result, as the products of the combustion, when the materials have not been properly mixed. Our object in all cases should be to render the materials pure, and the proportions so accurate, as to produce the greatest possible effect, which, of course, must depend on the formation and the consequent expansion of the gases. ”

“ This gas is formed by the combination of a part of the sulphur with the hydrogen of the water; whilst the oxygen, the other element of the water, goes to oxidize the metal and to acidify the remaining sulphur. Hence sulphate of iron, or green vitriol is produced. The experiment may be made in a common basin.
It is a remarkable fact, that spontaneous combustion, which takes place without the application of an ignited body, ensues in a variety of instances; and new facts daily occur, which show, that cases of this kind are more numerous than we had reason to suspect. ”

“ Charcoal will not burn in dry chlorine. It unites with a less proportion of oxygen, and forms carbonic oxide gas, which burns with a deep blue flame. This combination is formed by distilling in a red heat, a mixture of equal parts of iron filings and chalk. This gas mixed with chlorine gas, and exposed to the sun's rays, will unite with it, and form chlorocarbonic acid gas. Carbon unites with azote, and forms cyanogen, the base of Prussic acid. ”

“ I have often inflamed pyrophorus in nitrous oxide over mercury, by means of a wire strongly heated, but not ignited. The light produced by the ignition of pyrophorus in nitrous oxide is white, like that produced by it in oxygene: in nitrous gas it is red.
When pyrophorus burns out in nitrous oxide, a little increase of the volume of gas is produced. Strontian lime water agitated in this gas becomes clouded; but the quantity of carbonic acid formed is extremely minute. I have never made any delicate experiments on the combustion of pyrophorus in nitrous oxide. ”

“ This oxidizement of the metal, in proportion as it is more rapid, necessarily gives rise to the phenomena of combustion, which, in this, and the generality of instances, presupposes a combination with oxygen. The fire is, therefore, more brilliant, as the combustion is more rapid, and the metal may be oxidized in a greater or lesser degree, but not to a maximum. From the effect taking place in the air, as it does not ensue, or is not seen, in the case, it follows, that the iron receives for the support of its combustion the oxygen of the air. ”

“ Thus, arsenic will burn with a beautiful white flame in oxygen gas; iron and steel will burn also, affording a brilliant light; phosphorus and charcoal with a white, and sulphur with a beautiful blue flame; zinc with a green colour, &c.
Again, we know that a mixture of nitrate of strontia and charcoal will burn with a rose coloured flame; one part of boracic acid, and three of charcoal, with a green flame; one of nitrate of barytes, and four of charcoal, with a yellow flame; and equal parts of nitrate of lime and charcoal powder, with an orange flame. ”

“ Lead pyrophorus is made by heating dry tartrate of lead in a glass tube (closed at one end, and drawn out to a fine point at the other) until no more vapours are evolved. The open end of the tube is then to be sealed before the blowpipe. When the tube is broken and the contents shaken out into the air, they burn with a red flash.]
[Footnote 19: Page 216. Water-gas is formed by passing vapour of water over red-hot charcoal or coke. It is a mixture of hydrogen and carbonic oxide; each of which is an inflammable gas.]
Poster’s note: “combustion that makes!” ”

“ A scheme has been recently devised for supplying London with an inflammable mixture of gases to replace coal. The new gas, "pyrogen," as it is called, is a mixture of nitrogen and carbonic oxide, three-fourths by weight consisting of the latter gas. The combustion temperature of pyrogen is stated to be 2,700° Cent., and for heating-purposes the flame of the burning gas is to be allowed to raise some good radiating substance to incandesence in an ordinary grate. ”

“ Take equal parts of brown sugar and alum, and melt them in a ladle. Continue the heat, stirring them constantly until a spongy black mass is formed. Let this mass be reduced at once to powder, and introduced into a common green glass phial, of the capacity of about six ounces, previously coated outside with a mixture of pipe-clay and solution of borax. Immerse the phial in a crucible, filled with sand, closing the mouth of the former with a piece of charcoal, or a glass tube inserted in it. Upon the crucible being exposed to a red heat, an inflammable gas will escape, which will take fire. ”

“ As charcoal enters into the composition of gunpowder, and the effective force of powder depends considerably on the quality, as well as the proportion of charcoal, it is obvious for this purpose, it should be as pure as possible.
Carbon is always obtained from some of its combinations, as from pitch, tar, rosin, wood, and oil. Various processes are employed for this purpose. Thus, by the combustion of rosin and oil, as well as pitch, tar, turpentine, &c. a soot is [90] formed that collects, called lampblack, which is nothing more than the carbon or charcoal. ”

“ The products of combustion are carbonic acid and azote. (See Experiment 42.)
Experiment 55. If one measure of arsenuretted hydrogen gas, (obtained from an alloy of three parts of tin and one of arsenic, by treating it with muriatic acid) , and two measures of oxygen gas are mixed together, and the electric spark is passed through the mixture; a detonation will ensue, and water and arsenious acid be formed.
Experiment 56. If potassium be made to act upon a compound of chlorine and sulphur, called chloride of sulphur, an explosion will immediately ensue ”

“ The nascent hydrogen which unites with the nascent nitrogen during the combustion is also derived from the organic matter which always contains enough carbon to decompose the water formed in order to be oxidized to carbon dioxid. While at first, therefore, during combustion, the hydrogen may unite with the oxygen, it becomes again free by the oxidation of the carbon and in this condition unites with the nascent nitrogen to form ammonia. ”

“ To the distiller it is useful, as it destroys effectually the burnt or empyreumatic smell of liquor. When heated to eight hundred de [88] grees in the open air, it burns. In oxygen gas the combustion is brilliant, forming in both instances carbonic acid gas, called also aerial acid, fixed air, mephitic air, and calcareous acid. This acid is formed in a variety of processes, and is carbon saturated with oxygen.
Carbon exists in various states of combination, and many of the compounds into which it enters are inflammable; hence carbonic acid is generated in the combustion of coal, oils, fat, &c. ”

“ If the ignited precipitate is persistently discolored by particles of unburned carbon, moisten the mass with a drop or two of concentrated nitric acid and heat cautiously, finally igniting strongly. The acid will dissolve magnesium pyrophosphate from the surface of the particles of carbon, which will then burn away. Nitric acid also aids as an oxidizing agent in supplying oxygen for the combustion of the carbon.
From the weight of magnesium pyrophosphate (Mg_{2}P_{2}O_{7}) obtained, calculate the phosphoric anhydride (P_{2}O_{5}) in the sample of apatite. ”

“ A mixture of 100 litres of spirit and 21/2 litres of a mixture of 4 parts of wood-naphtha and 1 of pyridine bases; this spirit, the use of which is practically limited to heating and lighting purposes, may be mixed with 50 grs. of lavender or rosemary, in order to destroy the noxious odour of the pyridine bases. (2) a mixture of 100 litres of spirit, 11/4 litres of the naphtha-pyridine mixture described above, 1/4 litre of methyl violet solution, and from 2 to 20 litres of benzol; this fluid is limited to combustion in motors and agricultural engines. ”

“ It is also known, that charcoal, which contains hydrogen, when exposed to atmospheric air, will absorb oxygen, and form water; and during this combination, heat must be generated, by the emission of caloric from the oxygen gas. It is said, then, that in cases of spontaneous combustion, when nitre, sulphur, and charcoal, are mixed together, (unless water be added to prevent it) , this effect will ensue, and fire be produced. We know, however, that percussion is one source of heat ”

“ We must content ourselves with saying that most modern producers are of the form of a tower in which a thick bed of fuel is partially burnt and partly gasified under the action of a blast of air mixed with steam. The chemical actions that take place are complicated, but the final result is the production of a gas containing from 2 to 8 or 10 per cent. of carbonic acid, 10 to 20 per cent. of hydrogen, 8 to 25 per cent. of carbonic oxide (CO) , 1 to 3 per cent. methane (CH4) , and 45 to 60 per cent. of nitrogen, with varying quantities of moisture, tarry matter, and ammonia. ”