The amateur electrician, and especially the one interested in wireless telegraphy, soon reaches a point in his work when the desire becomes pressing for a spark coil of more than toy proportions and capacity. To experiment with X-ray tubes or send wireless messages several miles requires a coil giving substantial spark of several inches in length. Ade sciiption of how such coils can be made will be given in this series of articles, and the reader is assured that anyone using proper care and following these directions need have no apprehension that the result will be other than satisfactory, and the expert can produce results.

Induction Coil Making For Amateurs I Apparatus Nee 135

It is assumed that those working from these directions are fully informed as to the principles of coil construction, and have also determined the capacity and dimensions of the coils to be made, and desire only the information necessary to enable them to do the work so that the results will be equal to those desired.

As perfect insulation is one of the most important if not the most important, feature necessary to the proper and continuous working of a coil, the way this is secured will first be considered. Paraffine wax is one of the best substances yet discovered for insulating purposes, is easily applied and remains effective except in the hottest climates. A mixture of 4 parts paraffine, 1 part beeswax and 1 part resin is excellent; the proportion of beeswax being increased if the coil is to be used outdoors in cold or moist weather. Shellac varnish has the disadvantage of being extremely difficult to remove if for any reason the winding has to be undone and rewound. But whatever substance is used, it is quite necessary that all spaces be filled to saturation, and this includes the cotton or silk covering of the wire.

The method and utensils for applying the wax to the wire used in the secondary winding will now be described. While silk covered wire is preferable to cotton covered, as the covering is thinner and therefore allows more turns of wire to be wound within the inductive influence of the primary, the additional cost inclines many to use the cotton covered. Both kinds of the fine gauge used, (No. 34 for wireless and No. 36 for X-ray) come coiled upon spools, which have holes through the center permitting them to be mounted upon rods when winding.

Our apparatus requires, therefore, a holder for the spool of wire, a receptacle P for the paraffine wax, which is kept warm by a water bath W, a lamp L and stand S for heating the water, a rigging F, G, H, running the wire from the spool into the wax and out again and thence to the section winder. The latter device will be described in the next chapter, and is simply mentioned at this time so that in getting out the board upon which the parte are to be mounted, the proper size may be provided. A thick, flat board D about 24 x 15 in. should be obtained for this purpose. If the winder is to be run by the treadle wheel of a sewing machine, and such an arrangement is a very good one, some way of clamping the board to the machine table must be provided, or what is better, a table made of. the same height as the machine with some device for fastening securely together.

By having a fable, the work of getting the parts together for an evening's winding, and removing them afterwards, is greatly simplified, as the only adjustments necessary before beginning operations is to secure the table to the machine and connect the belt.

By referring to the sketch the arrangement will be quickly learned. The heating utensils for the wax require a tin can for the wax, L, which is supported by projections P at the top in a larger can W holding the water. This can should have a wire handle for convenience in handling. It is also supported above the lamp by a stand S, which can be made from a cover by cutting out a large round hole and then soldering on four legs made from strips cut from another can. As a suggestion as to sizes, the can for the wax may be the size used for canned peas or corn and the can for the water the size used for tomatoes, or a2-lb. coffee can.

On the can for the wax solder three lugsp, made from tin strips, the outer ends being turned over about 1/4 in. and forming a loose fit over the edge of the water can. These are to prevent the wax can from shifting about.

The lamp L is a simple alcohol lamp made from a short bottle with a wide mouth, like a vaseline bottle a short piece of quiil from a hen feather for the wick tube and a cork. Bore a hole in the cork, forming a tight fit for the quill. The wick can be made by twisting up several strands of soft cotton twine. Use grain alcohol. By first heating up the water and wax on a stove, the small lamp will supply sufficient heat to keep the wax fluid.

The frame for holding the spool containing the wire is made from two upright pieces G at the top and two pieces II descending therefrom which at the lower end holds the wheel B over which the wire runs in its passage through the wax. The principal requirement is that it shall be firm and the shafts fairly even so the spools A, B, C, will run evenly. A cross piece K connecting the two uprights is also a help. The three wheels for grinding the wire through the wax were made from small spools, those termed "twist" spools, in which V-shaped grooves were cut with a sharp knife and smoothed up with a file. The shafts upon which they were mounted were made by cutting off wire building nails of about 1/8 in. diameter. By consulting the drawing no difficulty should be experienced in constructing the parts mentioned and getting them into working order. Be sure and allow sufficient room between the top of the cans and under side of the frame so that the cans may be lifted from the stand, which is necessary in order to clear the lower guide wheel and frame. The winder will be described in the next chapter. In anticipation of it readers who are without a turning lathe should obtain a polishing head; one costing from 75 cents to $1.00 will answer.