The sludge passes to a special tank and is permitted to settle down to approximately 20 per cent. solid matter. It is then scooped up by bucket elevators to be lifted and discharged into another tank at the top of the building. This acts as the storage tank or hopper, whence it is moved automatically by means of screw conveyors and distributed among six hoppers. Each of these hoppers feeds a drying machine. The driers, set out in pairs with their brickwork casings and flues, occupy the upper room. The machines themselves comprise iron cylinders set in the brickwork and coal-fired furnaces. They are fitted with a specially designed gearing and pulley mechanism which gradually moves the crude wet sludge from the inlet towards the opposite end or outlet. Being exposed to heat during this passage the sludge is naturally deprived of the water it contains, this being evaporated to be led to the furnace where any offensive gases and other matter associated therewith in suspension are consumed before passing to the chimney to escape into the outer air. By the time the sludge reaches the outlet it has been completely dried. The arrangement of the feed from the hopper to the drier is such that only a measured quantity of sludge can be passed through in a given time, which ensures the condition of the sludge at the outlet being uniform. The provision of a similar measuring system at the outlet of the drier ensures only a measured quantity of sludge being discharged at that point. It will be observed that these protective devices guard against forcing the apparatus to the detriment of the delivered sludge which emerges from the drier in the form of a dry powder. If desired this residue may be burned. Mixed with coke it forms an excellent fuel, and can be employed towards raising the requisite steam to conduct the treatment of further sewage. But, in view of the fact that this powder contains about 15 per cent. of fat, its disposal as a fuel would constitute about the most wasteful conceivable. Accordingly, the next stage is the extraction of the fatty content. As it comes from the drying apparatus the sludge is passed automatically into a distilling retort which is bricked-in and heated. Above this retort is a tank containing acid, a certain quantity of which is passed into the retort to be automatically mixed with the powdered sludge. Simultaneously superheated steam is driven through the mass in such a manner as to permeate the whole. The interior of the retort is fitted with gearing and pulleys similar to those provided to the drier and for a similar purpose--the steady gradual movement of the sludge from one end to the other. By the time it has reached the outlet from the machine the sludge, completely deprived of fat, is automatically discharged as a valuable manure and is ready for distribution upon the land.