640 



Popular Science Monthly 



Electromagnetic Rotation of 

 an Electrolyte 



THE following interesting experiments 

 may be performed by. anyone possess- 

 ing an electromagnet. The apparatus used 

 is very simple and is shown in Fig. i. The 

 base -4 is a cardboard about 2 in. in 

 diameter and 5 is a 3^-in. brass tube 

 placed in the center of the cardboard. A 



A brass cylinder is fastened with sealing wax 

 on top of a magnet and holds the electrolyte 



brass cylinder C, 1 3^ in. to 2 in. in diameter, 

 is placed upon the cardboard. The sealing 

 wax D is placed in the bottom to secure 

 the cylinders and protect the cardboard. 

 It should be slightly concave, as shown, for 

 the mercury experiment. The part repre- 

 sented by£is an electromagnet. In its stead 

 the primary of an induction coil, or a strong 

 permanent magnet may be used, if an 

 electromagnet is not available. The electro- 

 magnet should be connected with a suit- 

 able source of direct current. 



A connection is soldered to the brass 

 cylinder at a point on its outer circum- 

 ference and a connection soldered to the 

 tube jB. These leads are connected with 

 one side of a reversing switch, as shown, the 

 battery being connected with the center. 



For the first experiment a fairly con- 

 centrated solution of potassium hydroxide 

 (KOH), or sodium hydroxide (NaOH), may 

 be used for the electrolyte. 



Now, if the field is excited and the revers- 

 ing switch closed, the electrolyte will rotate 

 about the tube in one direction. If either 

 the direction of the current or the polarity 

 of the magnetic field be reversed, but not 



both, the direction of rotation of the 

 electrolyte will be reversed also. 



If a drop of phenolpthalein is allowed to 

 fall into the solution when it is in motion, 

 ;t will give it a striated or lined appearance. 



If the strength of the magnetic field or 

 the current passing through the electrolyte 

 be increased, the speed of rotation is also 

 increased, and vice versa. 



In Fig. 2, a globule of mercury (Hg) 

 was placed in the solution, and one end of 

 a wire from the outer cylinder was brought 

 in contact with the mercury, the outer 

 cylinder being positive and the tube 

 charged negatively. The mercury was 

 flattened out considerably. 



In Fig. 3, a wire is connected with the tube 

 instead of the cylinder. When placed in the 

 mercury, it will stretch out in a straight 

 line from the tube to the cylinder. The 

 phenomena of the mercury will take place 

 without the magnetic field. If, however, 

 the field is applied, the center of the 

 mercury will be convexed in the direction 

 of rotation of the liquid. 



Sulphuric acid (H2SO4) may be used as 

 the electrolyte if a carbon cylinder and rod 

 are used. If a metal were to be used, the 

 acid would attack it, and the fumes given 

 off would drive the experimenter beyond 

 the range of observation. This arrange- 

 ment, however, will work better than the 

 hydroxide solutions. 



fy.S 



Manner of applying the current to the 

 electrolyte for making the experiments 



The pole that is charged positively at- 

 tracts the negative ions and vice versa. 

 Thus H2SO4, when ionized, splits up into 

 the positive ion H2, and the negative ion 

 SO4. These ions would move radially to- 

 ward the opposite pole, if there were no mag- 

 netic field applied. Upon the application 

 of a vertical magnetic field, the ions will be 

 given a circumferential component of mo- 

 tion. The circumferential component of 

 the viscous drag exerted by the moving 

 ions forces the electrolyte to revolve. 



