Page:Popular Science Monthly Volume 89.djvu/302

This page needs to be proofread.


��Popular Science Monthly

��pendulum can be adjusted to swing with a definite period of one second, or of two seconds, by changing the length of the string or rod, and in that way only.

Copper-Plating Leyden Jars

D. A. S., Midland Beach, Staten Island, N. Y., writes:

Q. I. Can you inform me how I may prepare glass in order that the surface may be copper- plated? How can I prevent blistering? I hear much these days of the copper-plated Leyden jar.

A. I. The process is rather e.xpensive. One manufacturer coats the bare glass with a cold silver solution such as is applied to the rear of mirrors. The jar is then placed in a furnace and heated near to the melting point whereupon the silver is thoroughly burned into the glass. The jar is then allowed to cool slowly and afterward placed in an ordinary electroplating vat and given a heavj' coating of copper.

Another manufacturer applies a cold silver solution to the inside of the glass and a coating of graphite held in place by shellac to the outside of the glass. The jar is placed in the electro- plating bath without burning.

Dimensions for Transmitting Transformer

A. W., Fayette, Ala., writes:

Q. I. Please give me the dimensions of the primary and secondary windings for an oscillation transformer for use with a I K.W. transmitting set. Please state the diameter of both windings.

A. I. It is assumed that you desire an oscillation transformer of the pancake type, and if so, it should have the follow-ing dimensions: The primary winding has eight turns of flat copper ribbon placed on an insulating support edgewise, the copper being about \ in. in width by 1/16 in. in thickness. The outside diameter of the winding is 10 ins. and the inside diameter about 4j ins.; the turns are therefore placed about J in. apart. The secondary winding of the oscillation transformer may consist of about 18 turns of the same size ribbon, also spaced \ in. apart. The outside diameter of this winding is 14 ins. and the inside diameter about \\ ins.

Q. 2. Should the ribbon be wound in the same direction in both windings?

A. 2. It makes no difference which way they are wound.

Q. 3. In the construction of a condenser for a I K.W. transformer, should the tinfoil be placed on both sides of the glass plates and the plates then stacked together so that the tinfoil of one plate touches the tinfoil of the other, and should the copper ribbon for making contact ■with the tinfoil be brought out l)etween the plates, and should the odd number of plates be

��connected to the right condenser terminal and the even numbers to the left, or vice versa? Would it be satisfactory to place the tinfoil on a glass plate, then lay on top of it another glass plate, followed by a second sheet of tinfoil, and so on throughout the series until complete?

A. 3. It is preferable to coat both sides with tinfoil and the best method is to place the foil on the glass plates with a good grade of fish glue, after which the plate is shellacked to prevent the foil from blistering. Alternate plates are con- nected to one terminal, and the inter\'ening plates to the inside terminal. The surfaces of the sheets of tinfoil from each plate should be pressed tight against the sheet ne.xt to it. The reason for this is that unless the tinfoil is firmly attached to the plates, a violent brush discharge takes place between the glass and the foil, causing blisters.

Q. 4. What should be the capacity in amperes for a transmitting key to break the primary circuit of a l-K.W. Iio-volt 6o-cycle transformer?

A. 4. Owing to phase displacement in the primary circuits an ammeter will indicate from 14 to 16 amperes, but of course with no phase displacement the ammeter should read about 9j amperes. The transmitting key should have a current-carrying capacity of 15 amperes.

Radio Frequency Changers W. H. H., Cold Spring, N. J., asks: Q. I. Will you kindly give me a more complete description of the transformer which doubles the frequency of the current imposed on the primary winding, which you mention in the article entitled "Long Distance Wireless Teleg- raphy" in the August IQ15 issue of this publi- cation.

A. I. It would be far too long an article to give in this column, but you w-ill find one of the most complete short descriptions of radio frequency changers in print in the March 1915, Volume 3, No. i issue of the Proceedings of The Institute of Radio Engineers. This is a 35-page article and it covers not only static but dynamic, electrostatic as well as electromagnetic, frequency changers. It is fully illustrated and contains many graphs showing the relations of the several currents during the frequency changers. If you are at all interested in the sub- ject, we most certainly recommend that you read this article. If you cannot obtain a copy of this publication from a library or member of the Institute you can purchase a copy for fl direct from the Institute Secretary, ill Broad- way, New York.

Q. 2. To what degree is the core of the transformer saturated by the direct current?

A. 2. The core is saturated to the point known as the knee of the curve. It is the point where the saturation begins to increase very slowly with increase of magnetizing current.

�� �