Explain the action of the sewage syphon.

This is a device made in several patented forms, all working somewhat on the same principle. The syphon is connected to the discharge chamber of the septic tank at its outlet. When the sewage in this chamber reaches a certain height it automatically starts the syphon which quickly syphons off the contents, delivering them into a pipe which conveys the sewage to the point of final disposal. (See page 113.)

Explain the chemical or bacterial action that takes place in the septic tank and is essential to its proper operation.

It will be seen that under ordinary conditions the heavy matter entering the tank, if carried off would foul the filter bed or sub-soil system very quickly, and if allowed to remain in its original state, would quickly fill the grit and settling chamber with disastrous results to the proper working of the plant.

Experiments of recent years have proved, however, that bacterial action, if allowed sufficient opportunity, will completely disintegrate and liquify almost all solid matter, even substances such as leather, bones, etc., provided it is of animal or vegetable matter. The bacteria which perform this work multiply rapidly, and live on the surface of the sewage and on the sides of the different compartments of the tank. It is essential, however, that they be left undisturbed. Consequently the entrance of waste and the overflow must be accomplished with as little commotion as possible. The solids rise to the top and form a sort of scum or crust, and upon the under side of this the bacteria make their strongest attack. In a very few hours bacterial action will disintegrate and liquify most substances naturally entering the sewage. It is essential that the operation of the syphon be at sufficiently long intervals to allow this bacterial action to take place completely.

Why does water begin to freeze at the surface?

For the reason that the surface is in contact with the air, and the air absorbs and carries away the heat of the water.

Water being a poor conductor, it is slow in freezing below the surface, only freezing as the water next to the ice becomes chilled and the heat contained passes out into the air through the pores of the ice.

Why does salt prevent the freezing of water?

Salt water freezes much more slowly than fresh, a temperature 25 degrees below freezing point being required in the freezing of salt water. This explains why salt thrown upon ice causes it to melt. The salt dissolves the crystals of ice, thereby forming a fluid. Whenever a solid is converted into a fluid, heat is absorbed, and the cold thereby made more intense. This explains why a mixture of salt and ice is a freezing mixture.

What is ventilation?

Ventilation is a continual change of air.

How can it be proven that the air of a room is in constant motion?

If a flame is held near the crevice at the top of a door, it will be noticed that the flame is blown outward, while if it is placed near the crevice at the floor, the flame will be blown inward.