Part 17 (1/2)

268 Connections The inside ends (-- 123) of the field-nets are held at 4 The outside end of coil 2 is joined to X, and that of coil 6 to 8, the foot of the brush which presses against 10 The section, 10, of the commutator is joined to 11, the outside end of coil 12, its inside end being fastened to the inside end of coil, 16, either by twisting the them under the top nuts of the armature yoke, 14 The outside end of coil 16 is joined to the other commutator section, 18 The brush, 19, co-post, Y

If the current enters at X, it will pass through 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and out at Y, provided 10 and 18 are in contact with 9 and 19 Be careful not to have any short circuits If, for example, the wire 7 touches 4, or if 3 touches 8, or if the wires 11 and 17 touch the shaft, your current will not pass where you expect, and you will have trouble

269 Adjustment The arnets as they turn This ulated by the thickness of A and the position of the nuts on the shaft, S B The slots in the commutator must be under the center of the yoke, 14 The brushes, 9 and 19, must touch 10 and 18, but not so hard that they will stop the motor

Wire brushes are more easily adjusted than tin or sheet-copper ones The tin arm, T, must hold the shaft properly The point of the shaft must allow it to turn easily The motor will turn clockwise if the attachood bi+chromate cells, like App 3 or 4

270 Operation The current will pass through the field-coils in the saed The current is reversed in the are from one section to the other of the co one-half of a revolution, and in the opposite direction during the other half This reverses the poles of the arnets every 1/2 revolution (See text-book for full explanations and for simple experiments with electric motors)

APPARATUS 147

_271 Attachnets for armature, etc, in which cores are used that are not 5/16 in in diaed Its 5/16 stove-bolt will have to be removed, and a 1/4 in one put in instead

Thisa handle for the 1/4 in bolt To keep this fro in the 5/16 hole, wind stiff paper around the bolt until it fits quite tightly The whole winder is explained as App 93

CHAPTER XX

ODDS AND ENDS

APPARATUS 148

_272 Graduated Circles_ Fig 123 For coalvano 123 is a reduced drawing fro lines are 10 degrees apart, the srees can be determined with considerable accuracy with the eye

[Illustration: Fig 123]

To divide the circle Divide the circurees frorees in every circle Divide each quarter into nine equal parts with a pair of dividers; these will be for the long lines, 10 degrees apart Divide each of these into two equal parts If you are used to drawing, you can divide the circle still ree divisions will do

APPARATUS 149

_273 Adjustable Table_ Fig 124 A table that can be raised or lowered is useful The one shown at D, Fig 124, is used for the galvanoure The upright piece, U, is fastened to D with brass screws, not with nails, as these would affect the needle It is placed at one side of D so that the compass needle placed in the center of D will also be in the center of the wire coils when used in App 117 The table is fastened in any position by a screw-eye, S I, which presses a copper washer, W, against U S I works through a narrow slot, S, and screws into the back of the galvanoer, the table may be used for other laboratory purposes, if it is joined with so 124]

APPARATUS 150

_274 Glue Pot_ If you have occasion to use glue, you canplaced inside the other Put 1/4 teacupful of glue in the inside can If you have time, cover it with cold water, and let it soften If you are in a hurry, cover it with hot water Set this inside can into the other, in which you have boiling water Do not let the water boil over The solder will not melt frolue with a little hot water until it drips frolue hot and fairly thin, and apply quickly Hold the pieces of wood together by pressure until the glue hardens

APPARATUS 151

_275 Paraffine Paper and Cardboard_ are extre purposes The paraffine used in candles will do, if you cannot get it in block form While ordinary paper will do for simple apparatus to wind about coils, etc, you will find that paraffine paper can be handled very rapidly To melt the paraffine you should use a double boiler, or one made of a shallow basin set in a pan of water The water should be boiled This will melt the paraffine in the basin Strips of paper just passed through the melted paraffine will become soaked, and the paraffine will quickly harden in the air Allow thick cardboard to soak for a minute or two, to drive out all the air This nets (See -- 119) To make one piece of this paper stick to another, merely pass a clean hot nail over the there they lap To hold coils of wire together, or to wooden bases, use a few drops of paraffine applied with a large hot nail

276 Caution Do not heat paraffine directly upon the fire or over a burner, unless you watch it constantly It will burn if its temperature is raised too lue

APPARATUS 152