358 



THE WORLD'S ADVANCE 



Chain Attachment for Snap Switch 



The accompanying drawing illustrates 

 a snap switch equipped with a scissors- 

 like ratchet and string to avoid the time- 

 consuming operation of feeling for the 

 knob and twisting it as is usually done. 



A little adjustment will be required to 

 determine the correct spring tension. 

 Contributed by 



DAVID SCHELL. 



Vise for Polished Pipe 



Polished pipe can be held in a vise 

 without scratching the surface if the 

 pipe is rolled in paper upon which plaster 

 of paris is plentifully sprinkled. 



Contributed by 



JACOB BLASS. 



Removing the Tarnish from Silver 



Tarnish may be removed from silver- 

 ware by means of a "silver tarnish bat- 

 tery." For the battery, a tin pail or a 

 pan is required, in the bottom of which 

 two strips of zinc are placed cross-wise. 

 These strips should be about one inch 

 wide and a little shorter than the diam- 

 eter of the containing vessel. The pail 

 should be half filled with hot water, and 

 for every quart of water four teaspoon- 

 fuls of salt and one of baking soda 

 should be added. 



To remove the tarnish, the silverware 



should be placed in the pail so that some 

 part of it comes in contact with the zinc 

 strips. The tarnish will disappear rap- 

 idly. The experiment should not be tried 

 with oxidized silver, as the electrolytic 

 action causes the oxidized surface to be 

 eaten off. 



Contributed by 



CLYDE MORGAN. 



A Polarity Indicator 



This instrument may be used for de- 

 termining the direction of a storage bat- 

 tery charging current. Its operation is 

 based on the fact that unlike magnetic 

 poles attract and like poles repel. 



The case is made from fibre or hard 

 rubber. The magnet core is made of 

 solid iron or soft steel it must be per- 

 manently magnetized. The pointed end 

 of the armature should have a known 

 polarity. The purpose of the weight 

 on the armature is to bring it back to an 

 upright position. The pointer should be 

 made of aluminum on account of the 

 lightness of that metal. The size of the 

 wire used on the magnet will depend upon 

 the current with which the instrument is 

 to be used. 



The dial should be marked according 

 to the following directions: Grasp the 



Fibre 



coil in the right hand, so that the fingers 

 encircle it in the direction of the north 

 pole. The dial may be divided in any 

 way, to indicate the direction of the cur- 

 rent. 



Contributed by 



CLARENCE POOL. 



