[Illustration: FIG. 69.--_F_ reads center of ell to end, _C_ reads center of ell to center of valve, _D_ reads center of valve to center of T, _E_ reads center of T to center of ell.]
Screw home the coupling on the right thread. Mark with a piece of chalk on the coupling and the pipe showing a point on each where the coupling makes tight. Take off the coupling and count the turns and make note of the number. Now do the same on the left thread and make a note of the number of threads. If the left thread has six turns and the right has four and one-half, then to insure that the left thread will be tight when the right thread is, the coupling must be put on the left thread one and one-half turns before it is started on the right thread. Now with four and one-half turns, the right and the left threads will both be tight. A little thought and practice will make this connection clear. If all the measurements in this exercise are not cut accurately, the right and left coupling will not go together.
The supplying of cold water to buildings and then piping it to the various fixtures makes a very interesting study. We have gone over the methods of laying and piping for the house service pipe. We will go over the different systems now employed to supply the water, quickly.
UNDERGROUND WATER.--In thinly populated districts the well is still employed to supply water to the building. The water is brought to the surface by means of a large bucket or by means of a pump. A well point can be driven into the ground until water is reached and then the water can be brought to the surface by means of a pump operated by hand or by power. The water can be forced to a tank that is open and elevated, or forced into a tank that is closed and put under pressure. From either tank the water will flow to any desired outlets. A windmill can be employed to furnish power to operate the pump. Water supply that is received directly from underground is by far the best to use. A cesspool or outhouse must not be allowed on the premises with a well, otherwise the well will be contaminated and unfit for domestic use. An open well is not as sanitary as a driven well, as the surface water and leaves, etc., get into it and decay and pollute the water, and soon make it unfit for domestic use.