﻿84 Dr. L. Bleekrode on some Experiments 



friction has been feeble. Rubbing against a zinc or a copper 

 plate acts in the same way, these metals showing positive elec- 

 trification, and the solid carbon dioxide gets negatively elec- 

 trified ; this is also the case when rubbed with cloth. The 

 readiness with which this substance acquires an electric 

 charge is the more remarkable, as the surface of the disk or 

 cylinder, from the very low temperature, is soon covered with 

 moisture turning to ice particles, but these disappear on 

 moving the hands over the surface. A more complicated case 

 of electrification ensues when the compact disk is simply laid 

 down on the plate of the electroscope. When freshly prepared 

 immediately after the contact, the leaves diverge to an extent 

 corresponding to a difference of potential of at least 200 volts, 

 and more as compared with that effected by a zinc- water-copper 

 battery. It is — E, and when the disk of carbon dioxide is now 

 removed without touching the metal, the leaves first collapse, 

 and diverge again directly, and now indicate + E. Sometimes, 

 when the substance has already been exposed to the atmo- 

 sphere for a time, no charge is immediately produced on 

 touching the electroscope, but afterwards, when it is taken 

 from the instrument, this still shows a positive charge. It is 

 not at once evident how to account for the production of the 

 two opposite electricities in this case*, as several causes may 

 have been at work. It appears to me that the chief part is 

 played by the carbon dioxide escaping in the state of gas 

 between the disk and the spot where it is in contact with the 

 plate of the electroscope. At this place it is lifted up and 

 down somewhat rapidly by the gas evolved, and it gets a 

 negative charge, for the same reason as when rubbed with 

 the hand as before stated, and no strong motion is required, 

 because of its high electric properties, as I have remarked. 

 The +E that is free is carried away with the current of gas, 

 and the negative charge of the disk may induce an opposite 

 one in the metallic plate, on which it is lying, and recom- 

 bination is prevented, because a fresh layer of gas is present 

 and prevents actual contact ; the positive charge of course 

 becomes apparent in the electroscope as soon as its inducing 

 electricity is removed with the disk of carbon dioxide. That 

 the action after a certain time is much lessened may perhaps 

 be due to the fact that the copper plate of the electroscope 

 after prolonged contact has become too cold to provoke a rapid 

 evolution of gas, or perhaps the surface of the carbon dioxide, 

 by atmospheric influence, has lost, to some extent, its electric 



* It is necessary, to avoid errors, to make the disk of carbon dioxide 

 neutral after each experiment: this may easily be done by moving it 

 rapidly to and fro in a gas-flame. 



