RAIN-WATER TANKS. 91 



(which should slope gently in the direction of the 

 said dip-hole), should be provided in making the 

 tanks. This will allow a full can or bucket of 

 water to be extracted from the tank as long as the 

 bottom is covered with the crystal fluid. A tank 

 21 feet long, 4} feet deep, with an average width of 

 3j feet (inside measurements), will hold about 2000 

 gallons of rain water. A 4j-inch tie-wall should 

 be built across the middle of the tank, leaving a 

 space of 4J inches from the floor-line in the centre 

 of division wall, to enable the water to rise in both 

 divisions at the same time. The top course of 

 brickwork should be built in cement, and the whole 

 surface of work should be afterwards faced with 

 compost, consisting one part of cement and three 

 of sharp sand. In excavating for a tank of the 

 dimensions given above when built, 9 inches more 

 should be added to the length and width, and 

 4^ inches to the depth. A few short lengths of 

 oak, 4 inches by 3 inches, placed across the tank 

 at intervals of about 3 feet, will afford ample sup- 

 port for the trellis pathway to rest on. 



Each block of span-roofed houses should have 

 two tanks of the description indicated run right 

 across the several houses constituting the block 

 one at the bottom and one half-way up the length, 

 a short length of lead pipe, say, six inches long, 

 two or three inches in diameter, with a flange on 



