Popular Science Monthly 



789 



making than the ordinary and cruder 

 apparatus. — Edwin' Jaspers. 



Interesting and Instructive 

 Electrical Experiments 



THE accompanying diagrams illustrate 

 three interesting electrical experi- 

 ments that may be made with the regular 

 lio-volt lighting current at practically no 

 expense whatever. The first demonstrates 



COMMON SALT^SODIUM PHOSPHATE 

 Experiment with salt water and phosphate 

 solutions for a rectifier and polarity indicator 



the electrolytic rectifier. Procure a strip of 

 lead and one of aluminum about i in. wide 

 and 3 or 4 in. long. Tack these to a piece 

 of wood so that they can be suspended in an 

 ordinary drinking glass as indicated. This 

 is the rectifier. Fill the glass about three- 

 fourths full of water and add about a 

 spoonful of sodium phosphate. 



Another glass should be provided and 

 filled with ordinary salt solution. Two 

 metal strips should be arranged in this 

 glass the same as in the other, except that 

 both must be of the same metal — copper, 

 tin or whatever is most convenient. Con- 

 nect up as shown with a i lo-volt alternat- 

 ing current, placing a i6-candlepower lamp 

 in the circuit. Immediately bubbles will 

 be seen rising from one of the strips in the 

 salt solution, thus indicating the negative 

 pole. Temporarily short-circuit the recti- 

 fier, and the difference between the two 

 strips in the salt solution will immediately 

 disappear as the current becomes alternat- 

 ing again. If a small galvanometer is at 

 hand place it in circuit, and it will be seen 

 that when the rectifier is in circuit the 

 needle is deflected, thus indicating a 

 current in one direction only. Short- 

 circuit the rectifier and no deflection occurs, 

 although more current is flowing, as 

 indicated by the increased brightness of the 

 lamp. If no galvanometer is available, 

 wrap some fine magnet wire around a 

 pocket compass and the same result will 

 be secured. 



It is a property of the electric current to 

 carry liquids along with it in its passage 

 through membranes. This property is 



Liquids are carried 

 with electric cixrrents 



made use of in electrotherapeutics where 

 certain medicaments are made to penetrate 

 the tissues by placing them in contact with 

 the skin and passing a current through the 

 liquid into the body. 

 This phenomenon 

 may be readily dis- 

 played by the simple 

 apparatus illustrated. 

 Procure tw^o blocks of 

 wood about i in. 

 thick and 2 in. square. 

 Hollow out the cen- 

 ters as indicated and 

 bore a hole at each 

 corner so that they 

 may be clamped to- 

 gether with screws. 

 Get two lengths of 

 3/16-in. glass tubing 

 3 or 4 in. long, and 



tightly insert these in the blocks as shown. 

 Also run in the tip of a wire at the center of 

 each block, after which shellac the spaces 

 hollowed out in order that they may with- 

 stand the liquid and avoid leaking. Place 

 a sheet of thin leather between the blocks 

 and clamp together. With an eye-dropper 

 fill the interior through the tubes with a 

 solution of common salt. Stop when the 

 level rises in the tubes so that it is plainly 

 visible above the wood. Now connect the 

 two inserted wires with a direct current, and 

 almost at once the level of the liquid in one 

 of the tubes will begin to rise rapidly. 

 Reverse the current and the liquid will rise 

 in the other tube. If iio-volt direct cur- 

 rent is available use it in series with a large 

 lamp, or several lamps in multiple. If only 

 alternating current is available, place the 

 small rectifier just described in the circuit 

 and the result will be the same. 



It is certainly mystifying at first glance to 



Experiment with a salt water solution to 

 illustrate the idea of difference of potential 



dip the tip of a wire into the center of a jar 

 of salty water and see two lamps light up 

 while a very small one remains dark, only 

 to light up when the wire is moved a little 

 off center — either way — without any change 

 having been made in the connections. The 



