The general, not to say universal, mode of emptying the fixed or excavated cesspools is to pump the contents into closed carts for transport.
“This operation is,” says Mr. Rammell, “performed with two descriptions of pumps, one working on what may be called the hydraulic principle, the other on the pneumatic. In the former, the valves are placed in the pipe communicating between the cesspool and the cart, and the matter itself is pumped. In the latter, the valves are placed beyond the cart, and the air being pumped out of the cart, the matter flows into it to fill up the vacuum so occasioned. The real principle is of course the same in both cases, the matter being forced up by atmospheric pressure. One advantage of the pneumatic system is, that there are no valves to impede the free passage of matter through the suction-pipe; another, that it permits the use of a pipe of larger diameter.
“The cart employed for the pneumatic system consists of an iron cylinder, mounted sometimes upon four, but generally upon two wheels, the latter arrangement being found to be the more convenient. Previous to use at the cesspool, the carts are drawn to a branch establishment, situate just within the Barrière du Combat, where they are exhausted of air with an air-pump, worked by steam power. A 12-horse engine erected there is capable of exhausting five carts at the same time; the vacuum produced being equal to 28⅜ inches (72 centimètres) of mercury. A cart (in good repair, and upon two wheels) will preserve a practical vacuum for 48 hours after exhaustion.”
The total weight of one of these carts when full is about 3 tons and 8 cwt. This is somewhat more than the weight of the contents of a London waggon employed in night-soil carriage. Three horses are attached to each cart.
When an opening into the cesspool has been effected, a suction-pipe on the pneumatic principle is laid from the cesspool to the cart. This pipe is 315/16 inches in diameter, and is in separate pieces of about 10 feet each, with others shorter (down even to 1 foot), to make up any exact length required. Two kinds are commonly used; one made of leather, having iron wire wound spirally inside to prevent collapse, the other of copper. The leather pipe is used where a certain degree of pliability is required; the copper for the straight parts of the line, and for determined curves; pieces struck from various radii being made for the purpose.
Gutta-percha has been tried as a substitute for leather in the piping, but was pronounced liable to split, and its use was abandoned. So with India-rubber in London.
The communication between the suction-pipe and the vehicle used by the nightmen is opened by withdrawing a plug by means of a forked rod into the “recess” (hollow) of the machine, an operation tasking the muscular powers of two men. This done, the cesspool contents rush into the cart, being forced up by the weight of the atmosphere to occupy the existing vacuum; this occupies about three minutes. The cart, however, is then but three-fourths filled with matter, the remaining fourth being occupied by the rarefied air previously in the cart, and by the air contained in the suction-pipe. This air is next withdrawn by the action of a small air-pump, worked usually by two, but sometimes by one man. The air-pump is placed on the ground at a little distance from the cesspool cart, and communicates with it by a flexible India-rubber tube, an inch in diameter. The air, as fast as it is pumped out, is forced through another India-rubber tube of similar dimensions, which communicates with a furnace, also placed on the ground at a little distance from the air-pump, the pump occupying the middle space between the cart and the furnace, the furnace and the pump being portable. To ascertain when the vehicle is full, a short glass tube is inserted in the end of the air-pipe (the end being of brass), and through this, with the help of a small lantern, the matter is seen to rise.
“The number of carts required for each operation,” states Mr. Rammell, “of course varies according to the size of the cesspool to be emptied; but as these contain on the average about five cartloads, that is the number usually sent.[78]
“In addition to the carts for the transport of the night-soil, a light-covered spring van drawn by one horse is used to carry the tools, &c., required in the process.
“These tools consist of—