Page:Popular Science Monthly Volume 91.djvu/649

 Popular Science Monthly

��633

���A Teeter Swing for Public or Private Playground

THE illustration shows a way to make a permanent amusement device for chil- dren's playgrounds. It is inexpensive to build and if erected will prove as attractive to children as many other more elaborate de- vices.

Two planks A 16 ft. long, 10 in. wide and 2 in. thick form the sup- port for the teeter B, which is made of two pipes, each 1 Y% in. in diameter and 9 ft. long. The seats C consist of a board strapped on the pipe ar- rangement D which provides an opening for the legs, mak- ing it almost impossible for a child to fall out of the seat. The support for the main pipes is shown at E, each end of which passes through the planks with a coupling on the ends to prevent the piece dropping out of the holes bored in the planks.

The plank ends are sunk into the ground at one end and fastened together with a bolt F. The piece G is made from i3^-in. pipe strapped to the planks at H. Window cord is at- tached at the ends /. Two children, even of very un- equal weight, can have an enjo ya b 1 e time on this swing, as the teeter is worked by pulling on the cords rather than by balancing weight. The riders can use their feet to help the movement. If required, a brake can be easily added to prevent the seats striking the ground. — James E. Noble.

��An Interesting Experiment with Sulphate of Soda

��A

��A playground teeter made swinging part and planks set

��of pipe and fittings for the in the ground for the supports

���Details of the parts for making a teeter swing

��N experiment of an unusual character may be made with a thoroughly sterilized glass rod and a supersaturated solution of sulphate of soda. The phenom- enon is so extraordinary that any one who may make the trial will find it difficult to clearly explain the result. To make it more interesting four glass tumblers should be used. Place them in a saucepan of cold water with their bottoms resting on cardboard, then bring the water to a boil. Meantime dissolve some sulphate of soda in an- other vessel, by pouring the soda sul- phate into boiling water until the water will take on no more. Now remove the tumblers and place them upon a board. Fill them with the saturated solution and stand them aside to cool in a place free from vibration. If this part of the work is done at night the solution will be quite cold in the morning and ready for the test. Do not disturb the contents of the tumblers, or crystallization will set in at once and spoil the experiment.

Take an ordinary round glass stirring- rod that is about 1 ft. long and 5/16 in. in diameter and clean it well; then in the flame of an alcohol or other burner heat about 3 in. on one end of the rod almost red hot and place it to cool in such a position that the heated end will not touch anything. As soon as cold, take the rod and dip the end that was heated into one of the tum- blers containing the solution. No action whatever will take place; but as soon as the other end is inserted, the salt will im- mediately start to crystallize and will rapidly continue to do so until the solution becomes a solid mass.

If each tumbler is stirred at the start with the sterilized end of the rod, the same performance will take place.

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