‘The old address, sir! You used to know it well enough!’ said the lawyer with a leer, as he took the hand which the baronet did not dare to refuse in sign of friendship; and so they parted.
COAL AND ITS PRODUCTS.
In an article which appeared in this Journal in August 1876, entitled The Age of the World, we endeavoured to explain how coal was produced, and how it might be regarded simply as stored-up heat and light, derived from the sun ages ago.
Apart from the varied uses of coal in its ordinary state, we owe an immense deal to the products which by chemical means we obtain from it; and it is our purpose in this paper to briefly review these products, and to shew how we have adapted them to our several wants.
The manufacture of gas is undoubtedly the most important feature in the modern history of coal. Natural reservoirs of inflammable air exist in many parts of the world, and have in many cases been turned to profitable account. In China, for instance, the evaporation of salt has for many years been carried on by the heat obtained by the combustion of gas which issues from the ground. Streets and buildings there have also been lighted by the same means. In our own country too, such eruptions of natural gas—which have generally manifested themselves during the operation of well-boring—have not been uncommon. But the gas so obtained is not the same as that which we get from the distillation of coal, although it forms one of its chief constituents. It is commonly called marsh-gas, from its constant presence in bogs and places where decaying vegetable matter abounds. The treacherous Will o’ the Wisp owes its origin to this gas. It also issues in large quantities from coal-beds, and diluted with air forms the dreadful compound called ‘fire-damp.’
The first recorded experiment relating to the production of true coal-gas was as early as the year 1660, when a country clergyman distilled some coal, collected the gas in bladders, and burnt it from a jet, for the amusement of his friends. Although this very suggestive experiment was communicated to the Royal Society, no action seems to have been taken upon it until the beginning of the present century, when the matter seems to have attained a more practical form. At this time one or two factories in Manchester and Birmingham were for the first time lighted with gas. The idea of illuminating an entire town by means of a chemical vapour seems to have met with much ridicule, and it was found necessary to employ lecturers to go about the country to shew people how such an apparent impossibility could be carried out. However, in spite of much opposition, part of London was lighted by gas in 1812; and three years later, Paris adopted the same system. The delay in the acceptance of gas-making among the industrial arts was no doubt largely due to the expressed opinion of several eminent chemists and others, who considered that such a mode of lighting our towns could never be realised, because of the supposed danger which it involved. Modern experience teaches us that it is at once the cheapest as well as the safest mode of illumination that we can as yet command. In the manufacture of gas, the coal is placed in iron retorts, which are subjected to a high temperature for about six hours, when the operation is finished, and the retorts are ready for a fresh charge. A residue of nearly pure carbon, in the form of coke, remains in the retort, whilst the varied products of the distillation are carried off by pipes into suitable receptacles. For the sake of convenience, we will at present name only three of these products—ammoniacal liquor, tar, and the gas itself. The first is the principal source of ammonia, one of the most useful substances known. It may be almost said of ammonia, as it has been remarked of sulphuric acid, that the prosperity of a country may be known by the quantity which it consumes. It is used by colour-makers, calico-printers, and in the manufacture of most of the textile fabrics; in cleansing and extracting grease from various kinds of cloth, in the preparation of leather, in galvanising iron, and in pewtering. The chemist would be almost helpless without its aid; whilst in medicine it is used in about twenty different forms as a most valuable stimulant. It is almost needless to say that ammonia was in general use long before the era of gas-manufacture, for life could hardly go on without it. In fact its very name is derived from its manufacture hundreds of years ago from animal refuse in a district of Libya where the deity Jupiter Ammon was worshipped. The old alchemists too obtained it from the distillation of deer’s horns; hence one preparation of it is still called spirit of hartshorn. There are many other sources of ammonia, for its presence in nature is universal; but all have sunk into insignificance since the gas-works have yielded such plentiful supplies.
Coal-tar in its crude state is not of very great importance, its use being confined to such rough work as the water-proofing of boats and the painting of outhouses and the like. But in the hands of the chemist its applications cannot be lightly regarded, in fact its distillation is of sufficient importance to form a distinct branch of trade. In this process coal-tar is separated into three different products—naphtha (which in a rectified state is the benzol of commerce); heavy or creosote oil, which is used almost exclusively for the preservation of railway sleepers; and the residue pitch. The last is of great use to shipbuilders, and has more recently found employment in the preparation of asphalt roofing and paving. But naphtha is by far the most important of the three substances, if it were only for its use as a solvent for both india-rubber and gutta-percha. No doubt, failing this, other solvents for caoutchouc would have been found; but naphtha is a particularly cheap and effective menstruum for the purpose; and when we consider the varied uses to which india-rubber and gutta-percha are now applied—from elastic hosiery to submarine cables—we must acknowledge that naphtha is a valuable addition to our manufacturing resources. It is a significant circumstance that the date of the introduction of manufactured india-rubber (by Mr Mackintosh) follows the general adoption of gas-lighting by only a few years. Previous to this, india-rubber was imported merely as a curiosity, its first use being to obliterate pencil-marks, for which purpose it was once advertised in London at the modest price of six shillings per square inch.
Besides its use as a solvent, benzol is of particular importance in yielding, when treated with nitric acid, a substance called aniline. The discovery of aniline is one of the most remarkable triumphs of chemistry, as applied to the advancement of a manufacturing industry. (Before the date of coal-tar it was obtained from indigo, and the name it bears is the Portuguese for that colour.) The production of aniline caused quite a revolution in the various trades which are dependent in any way upon the colour-manufacturer; for lithographers, paper-stainers, calico-printers, and especially dyers, owe their most brilliant tints to its aid. The various dyes which are now commonly retailed for household use are also derived from the same source. Aniline is an almost colourless liquid, of a peculiar vinous odour, which after exposure to the air, changes to a dark resinous matter. The treatment which it undergoes in producing the various colours (and nearly every colour of the rainbow can now be obtained from it), is of too complicated a nature to be of any interest to the general reader. Magenta, the advent of which some years back many of our readers will remember, was the first aniline dye which appeared. The other colours have followed in quick succession, nearly all of them being the subjects of one or more patents. It is questionable whether all these colours are strictly permanent; but it is a pleasing thought that the hues which in one form or another existed at a period long before mankind had a place in nature, are now reproduced for man’s delight and benefit.
Another very important product of gas-tar is carbolic acid, which is also largely employed for dyeing purposes. Its value as a disinfectant is too well known to need recapitulation here; but we may mention that its use as a preventive of disease was most abundantly proved during the last epidemic among our cattle. It is in general use in our hospitals, not only as a disinfectant, but also as an antiseptic both in the dressing of wounds and in the treatment of various skin diseases. Carbolic acid also yields a substance called picric acid, which, on account of its explosive properties when combined with potassium, has been proposed as a substitute for gunpowder. There are many other substances derived from the distillation of coal-tar, but at present they are only of interest to the experimental chemist.