The chief defects in plumbing and drainage are the following: (1) Earthen pipe drains become broken or their joints leak, and they saturate the ground under a house with sewage. (2) Tree roots break and clog drain pipes. (3) The pipes sometimes have not fall enough. (4) Drains without running traps admit sewer gas. (5) Rats burrow along a drain pipe from the sewer into the house and admit sewer gas. (6) When the soil pipe from a water-closet is exposed in cold weather it may freeze up or be clogged by urinary deposits. (7) Rats gnaw through lead pipes and joints. (8) Two or more closets or sinks with unventilated {204} traps on the same pipe will siphon back sewage. (9) Overflow pipes sometimes have no traps and they let in gas. (10) Ash pits near a house carry moisture to walls, (11) Cesspools leak through the soil. In planning a school-building the classrooms and the study-halls are the first things to be considered. The classrooms should be oblong, with the aisles running lengthwise. Each child should have at the least 15 square feet of floor space and 200 cubic feet of air space. A room 30 by 25 feet with a ceiling 13 feet from the floor will serve for 48 pupils and no more. This is the best size for a room when blackboards and maps are used in teaching, because a larger room sets the children in the back seats too far away to see without eye-strain. Dormitories should have at the least 300 cubic feet of air space for each child, and great care is to be taken in the ventilation. Children about 10 years of age require 11 hours of sleep; under 13 years, 10-1/2 hours; under 15 years, 10 hours; under 17 years, 9-1/2 hours; under 19 years, 9 hours. Do not make children get out of bed before seven o'clock in the morning; do not let them study before breakfast, and do not force them to work after half-past eight or nine o'clock at night until they are at the least 17 years of age. The hours for work should be: Ages Hours of work a week From 5 to 6 6 6 to 7 9 7 to 8 12 8 to 10 15 10 to 12 20 12 to 14 25 14 to 15 30 15 to 16 35 16 to 17 40 17 to 18 45 18 to 19 50 Work given for punishment must be included in these hours. No one, even an adult, should study for more than two hours at a time without an intermission for a few {205} minutes. In a boarding-school no one under any pretext, even on rainy days, should be permitted to study during recreation hours, and the deprivation of recreation to make up lessons is a relic of barbarism. If a teacher can not get class work done except by shutting up children during recreation hours, remove the teacher or expel the pupil.