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at the top of the scrubber, and the supply pipe from it is so arranged that the oil can be made to flow into one or all of the sections, as in cold weather the gas needs less scrubbing than in hot.

After passing through the scrubber, the oil is led along the bottom of the horizontal condensers and into the hydraulic main. It then passes into a small cistern containing a float, which is in connection with an indicator close by the taps which regulate the oil supply, so that the supply from the cistern can be regulated in such a way as to insure a constant rate of flow. In this way the oil passing to the retort is always flowing in an opposite direction to the gas. The oil generally employed in Young's process is what is known as. “ blue oil,” having on an average a specific gravity of about •850.

Each retort makes 500 cubic feet of gas per hour, and 53 cwt. of a very dense graphitic coke is left in the retort for each ton of oil decomposed. This coke collects near the back of the retort, and can be readily removed.

Plate VI. shows a Peebles plant, as erected by Messrs. R. and J. Dempster, Limited, of Manchester.

The most successful method of impregnating gas with the vapours of volatile hydrocarbons, suitable for dealing with large volumes of gas, is that of Messrs. Maxim and Clark, and which at tbe present time is in extensive operation. Attempts had previously been made to carburet gas by ineans of the vapours of volatile hydrocarbons, but these former efforts were not successful, the great difficulty experienced arising from the fact that all the commercial samples of naphtha are mixtures of various hydrocarbons, each having their own boiling point, and, as a result, they give up their more volatile constituents very freely at the beginning, while the amount rapidly diminishes as the boiling point of the residue becomes higher. The increase of evaporation with the increase of temperature further aggravated matters. Now, these defects are not so apparent when gas is carburetted in bulk, as the gas to a certain extent mixes in the gas-holder by diffusion, and a fairly even illuminating power is the result.

The Maxim-Clark process not only does away with the difficulties previously alluded to, but carburets the gas used in bulk, so that each portion of the gas obtains its proper share of hydrocarbon.

For small installations, the apparatus consists of a circular copper retort, which is kept automatically filled to a fixed level with gasoline from a reservoir outside the building. The retort is jacketed, and steam or hot water is passed round it, which volatilizes the gasoline. This passes over baffle plates in the top of the retort, and then through an automatic regulator into a small holder sealed with mercury. The gas to be carburetted has to pass through this holder, and as it does so the gasoline vapour is supplied to it in the following manner. The holder works on a vertical spindle, which passes down the tube into the gasoline retort, and is so arranged that, when the holder is grounded, i.e., when no gas is passing through, the opening is closed, and no gasoline can pass into the holder. As gas is admitted, so the holder rises and lifts the spindle with it, allowing the gasoline vapour to rush up through grooves cut in the bottom of it, which increase in size the higher the spindle is drawn, and so allow more gasoline to pass into the holder the more gas passes through

CHAPTER XXII.

THE MANUFACTURE OF SULPHATE OF AMMONIA.

HE operation of manufacturing sulphate of ammonia

(NH3) contained in the ammoniacal liquor, and neutralizing the same with sulphuric acid (H,80.) as per the following equation 2NH, + H SO, = (NH.), SO,

The process of making sulphate of ammonia from ammoniacal liquor is a very simple one, and the improved apparatus which has been introduced to gas-works during the last few years has further helped to make the manufacture of this product still more easy.

In small gas-works, where steam is not available, an under-fired still or boiler is used for the purpose of disengaging the ammonia from the liquor, but in larger works this method is not to be recommended, owing to the loss of fuel, and the disadvantage of liberating suddenly large volumes of sulphuretted hydrogen and other foul gases from the ammoniacal liquor when this reaches nearly to boiling point; the sudden liberation of these gases makes them difficult to deal with in order to avoid nuisance. The modern system is to use a continuous still, that is, to have the liquor always running in and out, the ammonia being taken out during its passage through the still.

Plate VII. shows a plan and elevation of a plant for making sulphate of ammonia on the continuous system, designed by Messrs. R. and J. Dempster, of Newton Heath, Manchester, who have acquired a well-earned reputation for work of this description. In this form of plant the heat required to drive off the ammonia is obtained from steam which is introduced at the bottom of the still as shown.

The ammoniacal liquor is first pumped into an overhead tank, and from thence flows through what is termed a super-heater, or economizer. Here the hot foul gases from the saturator pass through the apparatus in an opposite direction, heating the cold liquor to boiling point, at the same time cooling the hot gases ready for the condenser and purifier.

These gases can be purified in the ordinary way by oxide of iron, or they can be taken to a Claus kiln where the sulphur can be recovered in a pure form.

From the super-heater the liquor passes to the top of the main still, which is composed of a number of trays. These trays are perforated with holes, having flanges projecting upwards so as to secure a depth of about two and a half inches of liquid which is made to travel in a sinuous direction over each tray. These holes are covered with inverted troughs, serrated along their lower edges. Steam is admitted at the bottom of the still, and in its ascent boils up the liquor descending from tray to tray, and liberates the ammonia from the liquor, which is kept in a state of constant vibration.

Cream of lime is pumped into the bottom compartment of the main still from the lime mixer and pump shown in the corner of the sulphate house.

This is thoroughly mixed with the liquor which then flows through the secondary still where it is again treated to the vibrating action of steam and the whole of the fixed ammonia is in this

way

liberated. The effluent liquid then passes automatically through a deep syphon pot without the intervention of valves, etc. In some cases the waste heat from this liquor is utilized

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