The primary winding is wrapped with six layers of "empire cloth or paper." Empire cloths and papers are a yellow insulating material made by treating linen or paper with linseed oil.
Roll up a paper tube of five or six layers of paper so that the finished tube is two and one-half inches long and of proper inside diameter to just slip over the primary winding when the empire cloth or paper is in position.
The secondary is wound over this paper tube. It will be necessary to mount the tube on a round wooden mandrel fitted with a small crank or handle so that the tube may be revolved. A "winder" may be very easily made by mounting a round wooden stick of the same diameter as the inside of the paper tube in a pair of wooden supports. Bore a hole in one end of the stick and bend a piece of stiff wire in it so as to form a crank.
[Illustration: FIG. 112.—The Fixed Condenser.]
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Size Length Width Length Width No. of No. of
of of of of of Paper Tinfoil
Coil Paper Paper Tinfoil Tinfoil Sheets Sheets
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1/4 30 in. 4 3/8 30 in. 4 in. 5 4
in. in.
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1/2 30 in. 4 3/8 30 in. 4 in. 5 4
in. in.
───────────────────────────────────────────────────────────────────
1 in. 30 in. 4 3/8 30 in. 4 in. 7 6
in.
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The paper placed between each two layers of the secondary winding should be the special waxed paper which is made for that purpose.
Start and end each layer of wire one-half inch from the edges of the paper. Wind the wire in smooth, even layers, permitting each turn to touch the other, but none to lap over. Wind on two layers of waxed paper between each layer of wire and the next. The paper must be put on smoothly and evenly so as to afford a firm foundation for the next layer of wire.
The wire should never come nearer to the edges of the paper than one-half inch or the insulation of the secondary will be weak and the coil not liable to give a long spark.
The utmost care should be used not to break the wire. If it should break, the ends must be very carefully connected. The number of turns that each layer averages should be carefully noted so that by keeping a record of the number of layers it is possible to tell how many turns have been wound on. When five to six thousand turns have been wound on the secondary it is sufficiently large, and the outside end of the wire should be fastened and prevented from unwinding by securing it with a drop of sealing wax.
When winding a secondary remember that if at any point in the work, you allow the winding to become irregular or uneven, the irregularity will be much exaggerated on the succeeding layers. For this reason do not allow any irregularities to occur and if the wire tends to go unevenly, wind on two or three extra layers of the waxed paper to smooth it out.