70 ELEMENTS OF LABORATORY WORK 



CHAPTER V 



OBSERVATIONS OF CERTAIN MUTUAL CHANGES EXHIBITED 

 BY CERTAIN KINDS OF MATTER 



47. When Certain Bodies are rubbed together and sepa- 

 rated the Space near them exhibits Certain Properties. The 



most distinctive feature, and the one most easily exhibited, of 

 a so-called electrified body is that small portions of certain 

 kinds of matter in its neighbourhood are set in motion. 



This property may be shown by bringing a piece of sealing- 

 wax, which has been rubbed on flannel or cloth, near to a 

 piece of pith suspended by a silk fibre, or dry lath balanced on 

 a blunt point. Rapid movement towards the sealing-wax or 

 electrified body is seen, and sometimes the body after contact 

 moves away, and sometimes there is a repeated to-and-fro 

 movement. The region in which such displacements take place 

 is called the electric field. 



Amber, ebonite, glass, resin, gutta-percha, etc., rubbed 

 with flannel, silk, fur, etc., exhibit the same properties as 

 sealing-wax. These changes, however, do not take place until 

 the object rubbed and the rubber are separated. When they 

 are together brought near a light body no movement is 

 noticed, although each apart may cause considerable move- 

 ment. The act of separation is therefore essential. 



When a metal is rubbed by a piece of silk and tested like 

 the sealing-wax, no change is perceptible, but if the metal, 

 conveniently in the form of a rod, is firmly fixed to a glass rod, 

 which is held in the hand while the metal is rubbed, a move- 

 ment of a light body may be obtained. When this class of 

 bodies is touched by the hand, it suddenly loses this property. 



