Methane, tetrachlormethane, &c., to yield aromatic compounds when subjected to a high temperature, the so-called pyrogenetic reactions (from Greek 7rup, fire, and - yon, fco, I produce); the predominance of benzenoid, and related compounds-naphthalene, anthracene, phenanthrene, &c.-in coal-tar is probably to be associated with similar pyrocondensations.
In methane, CH 4, the hydrogen atoms are of equal value, and hence only one alcohol, viz.
The identity of the four valencies of the carbon atom follows from the fact that the heats of combustion of methane, ethane, propane, trimethyl methane, and tetramethyl methane, have a constant difference in the order given, viz.
The quinonoid structure of many coloured compounds has been proved experimentally, as, for example, by Hewitt for the benzene-azo-phenols, and Hantzsch for triaminotriphenyl methane and acridine derivatives; but, at the same time, many substances cannot be so explained.
Prior to 1830, little was known of the process other than that organic compounds generally yielded tarry and solid matters, but the discoveries of Liebig and Dumas (of acetone from acetates), of Mitscherlich (of benzene from benzoates) and of Persoz (of methane from acetates and lime) brought the operation into common laboratory practice.
Methane and its homologues give origin to the " paraffin " or " fatty series " of the general formula C,H 2, ,+ 1 000H, ethylene gives origin to the acrylic acid series, C n H 27, - 1 000H, and so on.
That of the alcohols, which only differ from the hydrocarbons by having a group OH, called hydroxyl, instead of H, hydrogen; these compounds, when derived from the above methane series of hydrocarbons, are expressed by the general formula C7,H27,+10H.
Molten copper absorbs carbon monoxide, hydrogen and sulphur dioxide; it also appears to decompose hydrocarbons (methane, ethane), absorbing the hydrogen and the carbon separating out.
In methane and ethane the hydrogen atoms are of equal value, and no matter which one may be substituted by another element or group the same compound will result.
Von Liebig (Ann., 1908, 360, p. 128), from a very complete discussion of triphenyl methane derivatives, concluded that the group i ng A A A was the only true organic chromophore, colour production, however, requiring another condition, usually the closing of a ring.
Discovered by Boyle in 1661, it was first carefully studied by Dumas and Peligot in 1831; its synthesis from its elements (through methane and methyl chloride) was effected by Berthelot in 1858.
This conception has rendered possible a clear idea of the linking or internal structure of the molecule, for example, in the most simple case, methane, CH 4, is expressed by H H-C-H H It is by this conception that possible and impossible compounds are at once fixed.
Considering the predicted series of compounds C7,H2,,+2, which is the well-known homologous series of methane, the first member, the possible of isomerism lies in that of a different linking of the carbon atoms. This first presents itself when four are present, i.e.
FLUORENE (a-diphenylene methane), C 13 H 10 or (C6H4)2CH2, a hydrocarbon found in coal-tar.
Similarly nascent methane may reduce iron salts, and the black mud in which these bacteria often occur owes its colour to the FeS formed.
A little hydrochloric acid, methylene diresorcin [(HO) 2 C 6 H 3] 2 CH 2, whilst with chloral hydrate, in the presence of potassium bisulphate, it yields the lactone of tetra-oxydiphenyl methane carboxylic acid (J.
The above equation may consequently be written, if x is the heat of formation of methane, -x+0 = -94300-(2 X 68300) +213800 x =17000 cal.
The equivalence of the four hydrogen atoms of methane rested on indirect evidence, e.g.
Methyl chloride CH 3 C1, is a gas, boiling at - 23°, obtained by chlorinating methane, or better, from methyl alcohol; wood spirit is treated with salt and sulphuric acid, or hydrochloric acid gas conducted into the boiling spirit in the presence of zinc chloride, the evolved gas being washed with potash and dried by sulphuric acid.
CHLOROFORM (trichlor-methane), CHC1 3, a valuable anaesthetic, a colourless liquid, possessing an agreeable smell and a pleasant taste.
When calcium sulphate is present, the nascent methane induces the formation of calcium carbonate, sulphuretted hydrogen and water.
Ethane, when heated to this degree, splits up into ethylene and hydrogen, whilst ethylene decomposes to methane and acetylene, and the acetylene at once polymerizes to benzene, styrolene, retene, &c. A portion also condenses, and at the same time loses some hydrogen, becoming naphthalene; and the compounds so formed by interactions amongst themselves build up the remainder of the hydrocarbons present in the coal tar, whilst the organic substances containing oxygen in the coal break down, and cause the formation of the phenols in the tar.
There is very little doubt that the general course of the decompositions follows these iines; but any such simple explanation of the actions taking place is rendered impossible by the fact that, instead of the breaking-down of the hydrocarbons being completed in the coal, and only secondary reactions taking place in the retort, in practice the hydrocarbons to a great extent leave the coal as the vapours of condensible hydrocarbons, and the breaking down of these to such simple gaseous compounds as ethylene is proceeding in the retort at the same time as the breaking up of the ethylene already formed into acetylene and methane, and the polymerization of the former into higher compounds.
The chief unsaturated hydrocarbons present in coal gas are: ethylene, C2H4, butylene, C 4 H 8, acetylene, C 2 H 2, benzene, C 6 H 61 and naphthalene,C 10 H 8, and the saturated hydrocarbons consist chieflyof methane, CH 4, and ethane, C2H6.
Thisas, which is made for 10 or I I minutes, contains from 23 to 32% carbon monoxide, 7 to I 5% carbon dioxide, 2 to 3% hydrogen, a little methane, 64 to 66% nitrogen, and has a heating value of 950 calories per cub.
By subtracting the value for CH 2, which may be derived from two substances belonging to the same homologous series, from the molecular refraction of methane, CH 4, the value of hydrogen is obtained; subtracting this from CH 2, the value of carbon is determined.
Confining ourselves to cases where titration methods are not employed, the general order is as follows: carbon dioxide, olefines, oxygen, carbon monoxide, hydrogen, methane and nitrogen (by difference).
Methane cannot be burnt in this way even when there is much hydrogen present, and several other methods have been proposed, such as mixing with air and aspirating over copper oxide heated to redness, or mixing with oxygen and burning in a platinum tube heated to redness, the carbon dioxide formed being estimated by absorption in potash.
Starting with a solid hydrocarbon of definite composition, it would be theoretically possible to decompose it entirely into carbon, hydrogen, ethylene and methane, and, by rapidly removing these from the heating zone before any secondary actions took place, to prevent formation of tar.
Moreover, these secondary products cannot be successfully reduced, by further heating, to simpler hydrocarbons of any high illuminating value, and such bodies as naphthalene and anthracene have so great a stability that, when once formed, they resist any efforts again to decompose them by heat, short of the temperature which breaks them up into methane, carbon and hydrogen.
But here again another mistaken idea arose, owing to a faulty method of estimating the benzene, and there is no doubt that methane is one of the most important of the hydrocarbons present, when the gas is burnt in such a way as to evolve from it the proper illuminating power, whilst the benzene vapour, small as the quantity is, comes next in importance and the ethylene last.
In carburetting poor coal gas with hydrocarbons from mineral oil it must be borne in mind that, as coal is undergoing distillation, a rich gas is given off in the earlier stages, but towards the end of the operation the gas is very poor in illuminants, the methane disappearing with the other hydrocarbons, and the increase in hydrogen being very marked.
The water-gas shows 4 to 5% carbon dioxide, 40% carbon monoxide, o 8% methane, 48 to 51% hydrogen, 4 or 5% nitrogen.
The simplest aliphatic compounds, such as diazo-methane, diazoethane, and azo-formic acid, are yellow; the diamide of the latter acid is orange-red.
It is decomposed by water with the formation of acetylene, methane, ethylene, &c. Lanthanum carbonate, La 2 CO 3 8H 2 O, occurs as the rare mineral lanthanite, forming greyish-white, pink or yellowish rhombic prisms. The atomic weight of lanthanum has been determined by B.
It may be prepared by distilling diphenylene ketone over zinc dust, or by heating it with hydriodic acid and phosphorus to 150-160° C.; and also by passing the vapour of diphenyl methane through a red hot tube.
The water-gas itself is made for 7 minutes, and has an average composition of 3.3% carbon dioxide, 44% carbon monoxide, o 4% methane, 48.6% hydrogen, 3.7% nitrogen, and a heating value of 2970 calories per cub.
A further generalization was effected by August Kekule, who rejected the hydrochloric acid type as unnecessary, and introduced the methane type and condensed mixed types.
Its tetramethyl-diamino derivative, which is formed by condensing formaldehyde with dimethyl-meta-aminophenol and subsequent elimination of water from the resulting diphenyl methane derivative, is the leuco base of pyronine, into which it passes by oxidation.
Benzene-azo-methane, C 6 H 5 N 2 CH 3, is a yellow oil which boils at 150° C. and is readily volatile in steam.