The gas-producer itself (figs. 3 and 4) works in the following manner:--The coal is supplied to the charging-box E every three hours or so, and slides down an inclined plane, the upper portion of which is solid and covered with firebricks. Upon this sloping bed the fuel is heated, and its volatile constituents are liberated, just as in a gas retort, leaving about 60 per cent. of carbonaceous matter, the complete combustion of which is brought about by the air which enters through the open part of the grate at the foot of the sloping bed. More carbonic acid gas is now evolved, and this non-combustible gas passes through the red-hot fuel, taking up in its passage another equivalent of carbon, and so becoming an inflammable gas, or what is called carbonic oxide. Should it be considered advisable to make use of steam, each cubic foot of which yields as much inflammable gas as five cubic feet of air, a pipe of water is allowed to run at the foot of the grate, and is there converted into steam by the radiant heat. The combustible gases now pass into the main gas flue, and inasmuch as this gas flue must contain an excess of pressure above the exterior air, so as to prevent the inroad of atmospheric air into the gas flue, and consequent partial combustion, the gas is allowed to rise--which it will do by its initial heat--some score of feet above the producers, and is carried horizontally through the wrought iron tube F into and then down into the furnace. The flat-lying tube being exposed to the air causes the gas in its passage through it to lose about 200° Fahr. of temperature, which increases its density, adds weight to the descending column of gas, and presses it on to the furnace. One estimable feature in this system of gas-producing is that the production can be arrested for half a day without deranging the producer, the fuel and brickwork being sufficiently bulky to maintain a dull red heat for that period. Air cannot enter the grate unless the gases given off in the producer are withdrawn to the furnace; and when the gas valve of the furnace is reopened, the production of the gases is once more continued.[188] [188] For a scientific description of the patent regenerative gas furnace which took the prize medal at the London Exhibition of 1862 and the _grand prix_ at the Paris Exposition of 1867, see the 'Journal of the Chemical Society' for July 1873; the lecture delivered by the late Professor Faraday at the Royal Institution on June 20, 1862; and the description published by Dr. Siemens, London, 1874. The minimum cost of a _complete_ establishment for cremation upon the foregoing model, i.e., for the furnace and gas-producer as given in Plate II., but not including a mortuary building, would be as under:--