two pairs of regenerators, each of which consists of a great number of small rectangular tubes, formed of refractory bricks: and while the products of combustion pass from one end of the combustion-chamber through one pair of these regenerators, and are thus deprived of nearly all the heat they contain before escaping into the atmosphere, the air by which combustion is effected in the combustion-chamber and which enters by its other end, is supplied through the other pair of regenerators, that have been previously heated to a very high temperature by the passage through them from the combustion-chamber of the products of combustion. The heat carried away from the combustion-chamber is thus brought back to it and economized. A very simple valve alters the connections in such a way that, when one pair of regenerators is being cooled by the passage through them, in succession, of air from the atmosphere, the other pair is being heated by the passage through them, in succession, of the products of combustion: the pair previously heated being placed in connection with the atmosphere, that the temperature of the air intended for the support of combustion may in traversing them be heated: and the pair previously cooled being placed in connection with the combustion-chamber, that they may absorb the heat which without them would pass into the atmosphere and be wasted. The alteration of this valve is the only portion of the apparatus that requires attention; it must be reversed about every half hour, but it would not be impossible to render even this movement automatic. The fuel is supplied to the gas-producer in large quantities at a time, and in such a way that it tumbles down of itself along an inclined plane, according as that in the lower part of the furnace is consumed: it is thus deposited on the intensely-ignited fuel according as it is required. The regenerators deprive the products of combustion so completely of their heat that when passing into the atmosphere, they are rarely hot enough to singe paper.

It is clear that the principle of the regenerator is not new: the ingenuity and value of the invention consists in its being the application of a principle already in use for another purpose. It has, indeed, been applied in various ways. Bolton adopted it to a certain extent when, in the beginning of this century, he invented the tubular boiler. The tubes, by subdividing the products of combustion, and exposing them to a largo surface suited to absorb their heat, greatly economized heat, by diminishing the quantity carried off into the atmosphere and the very great value of the principle has been proved by the almost general use of tubular boilers. The regenerator is, however, still more exactly represented by the well-known apparatus termed a "respirator," which performs

on a small scale, the very same office for the air passing to and from the lungs as Mr. Siemen's regenerator performs for that passing to and from the combustion-chamber. The wire gauze of the respirator absorbs the heat passing off with the gases which leave the lungs during expiration, and gives it back to those entering the lungs during inspiration. Thus, not only is cold air, which might be injurious to persons of a delicate constitution prevented from passing into the lungs, but the heat produced by combustion within the body is economized. The action, and, indeed, the very construction of the regenerator being so similar to those of the respirator, it is extraordinary that the latter was not invented long ago.

There is one drawback to a general use of the regenerative furnace the complicated form of the regenerators, and a comparatively expensive forms and material employed in its construction. Moreover, it cannot well be used, except on a large scale. One, at least, of the advantages possessed by the regenerative furnace may, however, be obtained by other and simpler means-the removal of the smoke nuisance, which involves the economization of fuel, and the prevention of mischief to health, as well as the production of that dingy hue, which casts a gloom over all our great centres of manufacture. Legislation, both here and in other countries, has not been wanting in efforts to put an end to the evils caused by pouring enormous quantities of dense smoke into the atmosphere, but its success has been only partial. Manufacturers are liable to a penalty of five pounds a day, if they do not consume their smoke; yet, such are their profits, and such, in some instances, the supposed necessities of trade, that they not unfrequently prefer paying this penalty to being, as they believe, impeded in carrying on their business. Nevertheless, it may be safely affirmed that there is no branch of manufacture that, for its existence, or even its prosperity, requires the production of unconsumed smoke. Nor is there any that would not be carried on more economically, were the smoke which for the most part consists in very valuable constituents of the fuel-consumed in the furnaces. There is nothing to prevent this, except the ignorance or apathy of manufacturers themselves. To no subject has science devoted more attention than that of the consumption of smoke; and in none has it been more successful, since, in revealing the laws of combustion, it has suggested the means by which the consumption of smoke may be easily effected-at least in the furnace of the manufacturer, where the production of heat is the only object sought to be attained.

The unburned carbon, which causes the dark colour of smoke, is both the most mischievous and most wasteful of its

constituents. To get rid of this is the special object of all attempts at smoke-prevention, and it involves no difficulty which science is unable to overcome. One of the most remarkable contrivances which have been suggested for the purpose, consists in burning the fuel from the upper surface downwards, so as to bring the inflammable gases, properly admixed with air, in contact with fuel at a high temperaturea principle which, in various ways, and for a long period, has been used for the purpose; though, from the imperfect methods employed for carrying it out, not with all the success that might have been expected. The method which has been found to answer best consists in admitting air and coal, in small quantities at a time, through the top of the furnace, the direction of the draught being downwards through the burning combustibles. With another, and very effective arrangement, a steam coil is placed behind the fire bridge. When the steam it contains is superheated, it is thrown on the burning fuel, and, mixing with the products of combustion, it keeps them at a proper temperature, until there is time, and a sufficient supply of air to effect their complete combustion.

But even less complicated means than these, suggested by science, have been found, when carefully used, sufficient to prevent the escape of smoke from the chimney. It is merely necessary to supply the fuel in small quantities at a time, and to place it at first outside that which is already in a state of intense ignition. The gases which are thus evolved, and have been properly mixed with air, pass over the burning fuel, and are consumed. So effective is this simple, but scientific mode of proceeding, that the French Government considers it sufficient to effect all that the law can reasonably require with regard to the consumption of smoke.

There is one kind of smoke produced in vast quantities, which is far more mischievous than any other-that evolved by copper-smelting works-and yet its prevention has hitherto scarcely been hoped for, even by the most sanguine. It is highly injurious to health, and so destructive to vegetation, that it is impossible for plants of any kind to exist within its influence; so that large sums are often paid by the owners of metallurgical establishments, as compensation for the damage which they cause. As in every other case in which smoke is permitted to escape into the atmosphere, but to a still greater extent, it supposes the loss of a valuable material.

Science has, however, at last suggested a way to prevent all the waste and mischief caused by this poisonous smoke. A chemist at Friberg has recently invented a roasting furnace, which not only prevents the passage of any deleterious substance into the atmosphere, but changes what has

hitherto been a source of annoyance and danger into the means of producing a considerable income. In the ordinary processes, the copper pyrites, after having been stamped, is formed with clay or loam into balls, which are dried, and then roasted in kilns; or the pyrites, having been pounded, is spread on beds of fire-clay, where it is exposed to a high temperature, being kept constantly stirred, for the purpose of exposing fresh surfaces to the air. The sulphurous vapours thus evolved pass directly into the atmosphere. In the improved method, a furnace which consists of a vertical chamber of fire-brick, and contains a number of horizontal bearers of the same material, regularly distributed through it is used. These bearers uniformly intercept the crushed ore as it is discharged from feeding-boxes at the top of the furnace; and when the flat surface of the upper bearer contains as much as it will hold, the surplus fall on the next lower, and from that to the one still lower, and so on, until it reaches the bottom, by which time it is considered to have parted with all its sulphur.

The gases evolved are transmitted to a large chamber, heating in their passage the pipes which supply air to the grate, and there deposit the dust from the roasted ore and the arsenious acid. They are then conveyed to the sulphuric acid chambers, where the sulphurous acid which they contain, and which has been produced by combustion of the sulphur contained in the copper pyrites, is condensed, sulphuric acid being formed from them in the usual way.

It has been calculated that from the copper smoke which hitherto has not only been wasted, but has been productive of so much mischief, 1000 tons of sulphuric acid may be made per week; and £4000 is said to have been paid to the inventor for the use of his patent right.

The next example to which I shall direct attention is one of the greatest triumphs ever achieved by science-the production of the most beautiful and valuable substances from coaltar, one of the most worthless and least attractive matters with which we are familiar. Long as coal-tar has been known it was not until recently even suspected to be the source whence might be derived a number of chemical compounds, rivalling the rainbow in the brilliancy of their tints, and capable of affording dye-stuffs fitted to supersede those previously obtained from the most distant regions, and costing immense

sums.

When coal-tar is distilled at a temperature gradually increasing in elevation, it affords, besides hydrogen, water, and ammonia, a number of neutral and basic substances, among which aniline ranks the highest in importance. So early as 1826, Unverdorben obtained from indigo a compound which,

from properties he found it to possess, he termed crystalline. Some years after Runge observed in the products obtained from coal-tar a material capable of affording, under the influence of chloride of lime, a beautiful violet, which he called kyanol. At a subsequent period, Fritzsche, when studying the properties of crystalline, came to the conclusion that aniline would be a more suitable designation for it; and about the same time Zinin produced a similar compound from coaltar, and gave it the name of benzidan. Still further investigation showed that crystalline or aniline, kyanol, and benzidan, were all identical, though derived from so very different sources; and it was found that this substance could be most conveniently procured from coal-tar; not, indeed, directly, but indirectly, by conversion of benzol, which is found in the tar in very large quantities.

Benzol is a striking illustration of the way in which the valuable properties of a substance may long remain dormant. It was discovered by Faraday in 1825; but it remained for years a mere scientific curiosity, though it may be obtained with ease, and to any amount, from the naphtha of coal-tar, by fractional distillation, its boiling point being 80° cent. It is readily converted into aniline, by submitting it to the action of fuming nitric acid: which transforms it into nitrobenzol, or nitrobenzine, the well known artificial essence of bitter almonds, discovered by Mitscherlich; and then changing the nitrobenzine into aniline, by means of reducing agents, such as sulphuretted hydrogen, or, which is usually employed in practice, acetic acid and metallic iron.

Aniline, though colourless, is the source of beautiful colours, the number of which is already very considerable, and is being continually increased. It was first observed in 1835, that a solution of chloride of lime imparts to it a blue colour; and in 1853 it was discovered that aniline violet, a blue-black precipitate, is thrown down from a cold dilute solution of aniline in sulphuric acid by a cold dilute solution of bichromate of potash. Aniline violet, which has received different names, may now be prepared in various ways.

In 1859, MM. Verquin and Renard practically discovered aniline red, or rosaniline. It is obtained without difficulty, by boiling for about a quarter of an hour a mixture containing ten per cent. aniline and about seven per cent. chloride of tin; the result being a liquid which is of so intense a colour as to appear almost black, but which is fitted at once, by mere dilution, for the use of the dyer. Rosaniline forms a number of very beautiful salts.

Aniline yellow, or crysaniline, another important derivative of aniline, is obtained from the residue which is left