Fig. 10 shows West's Charging Machine driven by a

cotton rope.

In the Foulis-Arrol system of stoking, the motive power is supplied by hydraulic pressure.

In the drawing machine, the rake is composed of a steel bar of H section, on the under side of which works a slide, to which is attached a steel rake rod.

On the upper side of the bar are fixed two hydraulic rams, one for the purpose of propelling the rake into the retort, the other for withdrawing it. A 1-inch circumference steel wire rope passes from a fixed point round a sheave on the end of each ram on to the slide, to give the required motion; the stroke of the rake being double that of the ram. The rake is suspended about the middle of its length by a steel wire rope connected with a vertical ram, by means of which it is raised and lowered to suit the heights of the several tiers of retorts.

The working of one lever performs the four successive operations of raising, propelling, lowering, and withdrawing the rake, and a second lever in connection with the vertical ram raises and lowers the rake bar. The whole is fixed within a light L-iron framework carried upon travellingwheels running on rails laid to a gauge of 7 feet 7 inches, and is easily propelled by one man by means of bevel gearing.

The water from the cylinders is conveyed, after being used, into a tank fixed at the top of the framing, from which the quantity required for cooling the rake head is drawn. The quantity can be regulated by the man in charge of the machine, the excess overflowing by a separate pipe.

The charging machine, fig. 11, somewhat resembles the drawing machine in its appearance and general construction, the main points of difference being the addition of a hopper for carrying, and the arrangements for delivering the coal.

The hopper is a fixture in the front, and on top of the machine, and will hold sufficient coal for charging twenty

retorts. This hopper is filled as required by a stationary overhead hopper, fixed above the retort settings, and supplied with coal by an elevator, the coal previously passing

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through a breaker. The coal is delivered into the retorts by a series of "pushes," effected by means of a rod with a plate at the end, connected to two hydraulic rams, as in the case of the rake, worked in precisely the same manner as the rake, the only difference being that the push-plate is of a different shape, and rather larger than the rake head. The charge of coal is delivered in front of this plate by means of a revolving drum fixed immediately under the hopper, and divided by radial partitions into a number of chambers. This drum has a continuous rotary motion imparted to it by the action of two small hydraulic rams, by means of a ratchet and pawl arrangement, the extent of the revolution of the drum determining the amount of coal discharged therefrom. This can be easily regulated to the amount required for the charge.

The connection between the machines and the mouthpiece of the retort is effected by a sliding plate, with shallow sides to it, controlled by the driver from the platform on which he stands, the plate being so constructed as to enter the mouthpiece about two inches. This plate receives the coal as it falls from the drum. It will be evident that, in charging a retort, each stroke of the pusher must be shorter than the preceding one, and, in order to automatically effect this shortening of the stroke, there is provided a revolving shaft, placed parallel with the charging ram, having fixed upon it, at equal distances, six stops or projections placed radially out of line.

The shaft being given a sixth of a turn by a ratchet and pawl arrangement, actuated by the lever which works the pusher, brings the stops successively in the path of the ram and shortens the stroke each time 16 inches until the seventh stroke, when the charge is complete. If it be desirable to miss the last stroke by reason of the mouthpiece of any retort being dull, the driver can operate the revolving shaft by means of a hand-wheel attached

thereto, and bring it into position for making the first or long stroke for the next retort.

The pusher with all its attachments, including a platform for the driver, is suspended, raised, and lowered in the same manner as the rake bar previously described. As in the rake, the movement of one lever, communicating with the valves, suffices for all the operations of charging the retort, with the exception of the adjustment of the sliding plate into the mouthpiece, which is worked independently by hand.

The hydraulic power is supplied by a duplex highpressure pumping engine, driving direct four single-acting plunger-pumps, working into an accumulator weighted to give a pressure of 400 lb. to the square inch.

The foregoing particulars have been obtained from a paper read by Mr. Joseph Tysoe before the Incorporated Institution of Gas Engineers in 1894.

CHAPTER V.

THE EFFECTS OF TEMPERATURE IN MODIFYING THE QUANTITY AND QUALITY OF THE GAS PROduced.

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HEN coal is subjected to the action of heat in a closed vessel it undergoes the process of destructive distillation, yielding various products, which may be broadly divided into solids (coke and retort carbon), liquids (tar and ammoniacal liquor), and gases consisting of the unpurified or crude coal-gas; and it is the effect of heat on the latter product which forms the subject of the present heading.

The quality and illuminating value of the gas produced from any sample of coal varies greatly with the condition of the coal at the time of distillation; whether it be old or fresh wrought, whether wet or dry. The temperature at which the distillation is conducted is, however, the most important factor in the ultimate results obtained. As would be naturally inferred from a study of the elementary composition of coal, the chief products of the distillation are compounds of carbon and hydrogen, the greatest portion of the carbon in the original coal being left behind in the retort in the form of coke. These compounds of carbon and hydrogen are produced in three different forms, viz., gaseous, liquid, and solid, as previously pointed out.

It is one of the canons of organic chemistry that the higher the temperature and the more advanced the decomposition of a substance, the simpler are the products thus produced; and so, when an organic substance such as