The gas producers which I prefer to use are of rectangular shape, so that a number of them can be put into a row. They are six feet wide and 12 feet long inside. The air is introduced and the ashes removed at the two small sides of the producer which taper toward the middle and are closed at the bottom by a water lute of sufficient depth for the pressure under which the air is forced in, equal to about 4 inches of water. The ashes are taken out from underneath the water, the producers having no grate or fire bars at all. The air enters just above the level of the water through a pipe connected with the blower. These small sides of the producer rest upon cast iron plates lined to a certain height with brickwork, and this brickwork is carried by horizontal cast iron plates above the air entrance. In this way a chamber is formed of triangular shape, one side of which is closed by the ashes, and thus the air is distributed over the whole width of the producer.

The gas is taken out in the middle of the top of the producer by an iron pipe, and fuel charged in by hoppers on both sides of this pipe. Between the pipe and the hoppers two hanging arches are put into the producers a certain distance down, and the fuel is kept above the bottom level of these hanging arches. This compels the products of distillation, produced when fresh fuel is charged in, to pass through the incandescent fuel between the two hanging arches, whereby the tarry products are to a considerable extent converted into permanent gas, and the coal dust arising from the charging is kept back in the producer.

The details of construction of this plant will be easily understood by reference to the diagrams before you.

The fuel we use is a common kind of slack, and contains, on an average, 33.5 per cent. of volatile matter, including water, and 11.5 per cent. of ashes, leaving 55 per cent. of non-volatile carbon.

The cinders which we take out of the producer contain, on an average, 33 per cent. of carbon. Of this we recover about one-half by riddling or picking, which we return to the producer. The amount of unburnt carbon lost in the cinders is thus not more than 3 per cent. to 4 per cent. on the weight of fuel used.

The gas we obtain contains, in a dry state, on an average, 15 per cent. of carbonic acid, 10 per cent. of carbonic oxide, 23 per cent. of hydrogen, 3 per cent. of hydrocarbons, and 49 per cent. of nitrogen.

The caloric value of this gas is very nearly equal to 73 per cent. of the caloric value of the fuel used, but in using this gas for heating purposes, such as raising steam or making salt, we utilize the heat it can give very much better than in burning fuel, as we can completely burn it with almost the theoretical quantity of air, so that the products of combustion resulting do not contain more than 1 to 2 per cent. of free oxygen. Consequently the heat escaping into the chimney is very much less than when fuel is burnt direct, and we arrive at evaporating, by means of the gas, 85 per cent. of the water that we would evaporate by burning the fuel direct, in ordinary fireplaces.

We have, however, to use a certain quantity of steam in the producers and in evaporating the sulphate of ammonia liquors, which has to be deducted from the steam that can be raised by the gas in order to get at the quantity of available steam therefrom obtainable. The former amounts, as already stated, to 0.6 ton, the latter to 0.1 ton of steam per ton of fuel burnt, making a total of 0.7 ton. The gas obtained from one ton of fuel evaporates 5.8 tons of water in good steam boilers, working at a rate of evaporation of 50 to 55 tons per 24 hours under 90 lb. pressure. Deducting from this the 0.7 ton necessary for working the plant leaves an available amount of steam raised by the gas from one ton of fuel of 5.1 tons, equal to 75 per cent. of the steam that we can obtain from the same fuel by hand firing.

In addition to the gas, we obtain about 3 per cent. of tar from the fuel. This tar is very thick, and of little commercial value. It contains only 4 per cent. of oils volatile below 200° C., and 38 per cent. of oils of a higher boiling point, consisting mostly of creosote oils very similar to those obtained from blast furnaces; and only small quantities of anthracene and paraffin wax.

I have made no attempts to utilize this tar except as fuel. It evaporates nearly twice as much water as its weight of coal, and we have thus to add its evaporative efficiency to that of the gas given above, leading to a total of about 80 per cent. of the evaporative efficiency of the fuel used in the producers. The loss involved in gasifying the fuel to recover the ammonia therefrom amounts thus to 20 per cent. of the fuel used. This means that, where we have now to burn 100 tons of fuel, we shall have to burn 125 tons in the producers in order to obtain ammonia equal to about half the nitrogen contained therein. Our actual yield of ammonia on a large scale amounting on an average to 32 kilos., equal to 70.6 lb. per ton of fuel, 125 tons of fuel will turn out 4 tons of sulphate of ammonia. We thus consume 6.25 tons of fuel for every ton of sulphate obtained, or nearly the same quantity as is used in producing a ton of caustic soda by the Le Blanc process - a product not more than half the value of ammonium sulphate.

At present prices in Northwich this fuel represents a value of 35s. If we add to this the extra cost of labor over and above the cost of burning fuel in ordinary fireplaces, the cost of sulphuric acid, bags, etc., we come to a total of 4l. 10s. to 5l. per ton of sulphate of ammonia, which at the present selling price of this article, say 12l. per ton, leaves, after a liberal allowance for wear and tear of plant, an ample margin of profit. With a rise in the price of fuel, this margin, however, rapidly decreases, and the working of the process will, of course, be much more expensive on a small scale, as will also be the cost of the plant, which under all circumstances is very considerable. The great advantages incidental to this process over and above the profit arising from the manufacture of sulphate of ammonia, viz., the absolute impossibility of producing smoke and the great regularity of the heating resulting from the use of gas, are, therefore, as far as I can see for the present, only available for large consumers of cheap fuel.