with melted pitch, heat being at once applied. As soon as distillation begins, the fire is moderated, in order to obviate boiling over, which, however, does not readily occur. When a certain quantity of heavy oil has passed over, an equal volume of melted pitch is introduced through a vertical tube, which passes through the dome of the still, and dips into the boiling pitch to half its depth, and which is capable of being opened and stoppered. In this manner the level of the pitch within the still is kept nearly constant. Thus as much more pitch is gradually introduced as the still originally contained. At the same time the superheated steam and the current of air deprived of its free oxygen are caused to sweep directly over the surface of the boiling pitch, or are even conducted into it. In this manner the vapours of anthracen are mechanically swept away, and condense partly in a fused state, but partly as a crystalline sublimate.

The still is not to be heated too violently, lest the pitch should burn on its bottom, and lest it should be difficult to observe the progress of the operation. Great care must be taken that too much orange vapour of chrysen, pyren, and benzerythen does not pass over, which would greatly complicate the subsequent purification of the anthracen. Towards the end of the process the distillation may be regarded as sublimation.

In most cases the residue in the still is sufficiently liquid to be run off, whilst hot, in the ordinary manner.

If it is too thick to flow off, it is not difficult to arrange the whole apparatus so that the neck of the still can be closed, and thus a pressure of to an atmosphere can be produced in the body by the influx of steam or air, which greatly assists in the escape of the pitch.

If it were desired to heat the pitch till carbonised, this could not be done in an iron still, partly from the difficulty of subsequently extracting the charred mass, and partly because the iron would be quickly worn out and destroyed.

It is therefore better to use either fire-clay retorts, like gasretorts, or still better muffle-furnaces, which latter are not only less costly, but admit of the treatment of larger quantities at once.

These furnaces consist of an arch rising from a hearth, under which the fire is conducted. Such a furnace may be five metres in length, two in breadth, and the same in height to the crown of the arch. The fire-box is placed under one of the ends of the arched space, and the flues range backwards and forwards in the direction of the sides, and are conducted on the opposite end into a main flue leading to the chimney. The man-hole is also in one of the ends, and is walled up before the fire is kindled, a cast-iron frame with sliding doors having been first fixed in.

In the middle of the furnace vault there is a round aperture through which the furnace is charged with pitch; and which is then again carefully closed.

The pitch can be introduced either in blocks, or in a liquid state. In the latter case it is melted in a large iron tank fixed above the furnace, and heated by the hot air passing through the flues before entering the chimney. If needful, the pitch may be melted over a separate fire. Near the crown of the arch, in the flat, vertical end-wall, opposite the fire-box, there is a moderately large round aperture in which is fixed an iron pipe, to conduct away the condensing vapours. If the pipe is sufficiently long the condensation is effected by contact with the air, but a shorter pipe may be used if water is applied, hot at first and afterwards boiling. A branch pipe leads the uncondensed vapours and combustible gases into the fire-box, where they are consumed.

Towards the end of the operation, which may be known by the condensation-pipe growing cold, the fire is allowed to go out. Some time afterwards the above-mentioned iron sliding door is cautiously opened, after a part of the brickwork has been removed, and the condensation-pipe has been

closed. The dense vapours in the interior of the furnace catch fire and burn. Without this precaution the residual coke would still contain pitchy particles, which by the arrangement just described are burnt away, leaving the coke quite pure. When the vapours are consumed, the fire in the interior of the furnace expires, as the access of air is insufficient for the combustion of the coke. The man-hole is then entirely broken open; the coke, still glowing, is extracted and quenched with water. It yields a fine, hard, porous product, almost free from sulphur compounds and from ash, and finds a variety of useful applications.

On account of the difficulty encountered in working up. anthracen contaminated with pyren, chrysen, and other hydrocarbons, boiling at high temperatures, it will always be necessary to submit the oils obtained from the carbonisation of the pitch to re-distillation and rectification.

Since even pure anthracen is partially decomposed on distillation, the process must be conducted with the aid of a current of superheated steam, or of hot gas freed from oxygen, and the operation must be broken off as soon as the above-mentioned less volatile hydrocarbons begin to distil

over.

The temperature of 360°-380° should not be exceeded, and towards the end of the process the distillation becomes a true sublimation, the anthracen escaping not as a liquid, but as a powder-sometimes even crystalline.

According to whichever method the crude, smeary, thickflowing anthraceniferous mass has been obtained, it must be submitted to a process of purification, depending mainly on the following principles :—

1. Leaving the heavy oils for some days in a cool place, that the anthracen may be deposited as completely as pos

sible.

2. Filtration, preferably by a filter-press, to separate the liquids from the solids, If it is simply filtered, as is often

necessary, the centrifugal machine may be used before the first pressing.

3. Pressing the mass twice after removal from the centrifugals; the first time cold, the second time with the simultaneous application of a temperature of 30°, 40°, or even 50°. The pressure must be applied with great care, a very powerful hydraulic press being preferably employed. The oils obtained on pressing often yield, if allowed to settle in a cool place, a small further amount of anthracen. After pressure the mass should be perfectly dry, readily friable and capable of being sifted.

4. Washing the finely-ground product with benzol, light petroleum oils, ligroin, &c. The light, volatile benzines and naphthenes readily dissolve the liquid oils, naphthalin, phenol, &c., without at the same time dissolving appreciable quantities of anthracen. If the lixiviation takes place at a boiling heat, which is often preferable, the anthracen dissolved by the benzol or petroleum naphtha is re-deposited as the solvent cools.

5. The lixiviated anthracen is then placed in a centrifugal machine, or strongly pressed, and is removed to the drying-room.

For the purification of anthracen the most varied means have been proposed. It is recommended to be treated with solvents, sometimes cold and sometimes hot. Some propose alcohol or ligroin, others benzol, naphtha, or even bisulphide of carbon. Some of these detergents are very unpractical, either on account of their high price, their volatility, or from their power of dissolving too much anthracen.

Thus, at common temperatures:

anthracen, but if it is contaminated with various other low hydrocarbons, as is the case with crude anthracen, its solubility in the above-mentioned purifying agents is considerably increased. Alcohol and bisulphide of carbon must be at once rejected, on account of their high price and their great volatility. Ligroin is cheap, but does not work well. Benzol is too dear. The best purifying agent is heavy naphtha, the so-called 'solvent naphtha,' a mixture of the higher hydrocarbons, which begins to boil about 120° C. The method of purification to be adopted depends on the percentage of pure anthracen in the crude sample. A determination of anthraquinon is first made according to the method described below, and the crude anthracen is then divided into two classes, such as contain less than 25 per cent. of real anthracen, and such as contain more.

The former kind is first treated in the cold with about 25 per cent. of naphtha in an iron washing-apparatus, consisting of cylinders fitted with mechanical agitators. The anthracen and the naphtha are introduced, the agitator is set in motion, and the mixture is stirred for twenty-four hours. The whole is then thrown upon a filter, which is made as air-tight as possible, in order to prevent the evaporation of the naphtha, and the solvent is removed either by atmospheric pressure or by the application of a vacuum. The naphtha which drains away is distilled off, the residue left in the still is let off whilst hot, and after cooling subjected to hydraulic pressure, and further treated like crude anthracen. The anthracen taken from the filter, once washed, is exposed to very strong hydraulic pressure, and contains then from 30 to 35 per cent. of anthracen. The pressed cakes are ground and treated exactly like crude anthracen, containing more than 25 per cent. of actual anthracen.

Anthracen containing from 25 to 50 per cent. of actual anthracen, is ground fine, sifted, and then placed in the washing cylinder, with an equal weight of naphtha, and