Page:Popular Science Monthly Volume 91.djvu/976

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960

��Popular Science Monthly

��dicular D-C whose value represents the equivalent of the three resistances in parallel. This equivalent combined in a similar manner with the remaining re- sistances of 225 ohms gives us the line F-G whose value according to the above scale is 120 ohms and represents the combined resistances of the four resistances in parallel. With the four resistances selected this result can be easily verified by the usual method of calculation.

This process may be carried out for any number of resistances. It is evident that the larger the scale selected the more accurate will be the result. The writer has personally found the foregoing method very convenient and more satisfactory than the usual methods, especially where tables of logarithms or reciprocals are not easily available. — F. H. Tillotson.

��Lighting the Dash-Board of an -Auto- mobile from the Side Light

MANY cars are equipped with the so- called flush side light, the lens be- ing flush with the out- side, and the back of the lamp ex- tending in on the dash. By simply cutting away a sec- tion of the lamp casing, as shown, part of the light will fol- low the dash, thereby illuminating it sufficiently for all needs. — Thos. W. Benson.

���A cut-out on the flush side light to illuminate the dash

��Heating a Soldering Iron with an Electric Arc

EXPERIMENTERS often find them- selves with some soldering to do, but with no means of heating the soldering iron. Using the iron as one electrode of an arc I found to be a good makeshift. • This suggested the construction of the arc and brackets described herewith. As it is to be used only a short while at a time, and the amperage is small, wood may be used in its construction but it is best to cover the wood with asbestos. Two stand-

��ards are fastened upright upon the base as shown and near the top of each is placed a screw hook (a nail bent up will do) upon

���The soldering iron makes one terminal for the electric arc which heats it

which the iron is to rest. A lever having a hole bored at one end, in which is inserted an ordinary }^-in. arc light carbon is pivoted at its center on a bolt which runs through the middle of the upright. The nut is tightened just enough to hold this lever in whatever position it is placed. As the carbon burns away, adjustment is made with this lever. One binding-post is con- nected with the hook which supports the iron and the other is connected by a flexible cord with the set screw which holds the carbon in the lever.

This is connected with the line by a resistance in series. A water rheostat which is easily constructed and regulated may be used, or a wire rheostat may be constructed. For a medium-size iron I found 3 amperes was about right. Lower- ing the resistance will increase the current and consequently the heat of the iron. If direct current is used it is best to connect the positive wire with the carbon, as this will avoid the possibility of pitting the iron. — Kenneth M. Bard.

��Sheet Asbestos to Make a Packing for Steam Chests

OWING to the heat imparted to the cylinders and steam chests of steam engines, rubber packing does not give as good service and last as long as it should. After some experimenting, the writer has found that a sheet of asbestos 1/16 in. thick makes a good packing for a team chest. This material is very cheap, and if put on the engine* wet, will stand a pressure of 150 lb. As an experiment, a joint made with the asbestos sheeting was taken apart and put together five times and still held its shape. Experience shows, that it makes just as tight a joint as the best rubber packing. — W. S. Standiford.

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