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.
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