﻿with Carbon Dioxide in the Solid Stale. 83 



that in general it was negatively electrified. The gas jet, 

 escaping through the hag, charged the electroscope with posi- 

 tive electricity when very near to the cloth, hut frequently, when 

 at some distance, the instrument indicated a negative charge, 

 when struck by the gas-current. When the hag was inserted 

 in a cylinder of narrow copper gauze I got sparks of more than 

 2 centim. when approaching a metallic conductor. A year 

 ago Wesendonk * published an extensive research bearing on 

 the question whether electricityis actually generated by friction 

 of gases against metals, already treated by Faraday f, and he 

 came to the conclusion that the gaseous state does not develop 

 electricity, and if indeed a charge manifests itself in the 

 electroscope, it is due to the fact that the gas contains mois- 

 ture or particles of dust. Experiments were made with air, 

 oxygen, and carbon dioxide under high pressure, and he stated 

 that the latter gas is very apt to develop electricity, because 

 aqueous vapour so easily condenses from the surrounding air 

 about the expanding current of gas which is at very low 

 temperature. 



It seems to me that great importance is to be ascribed to 

 the minute particles of solid carbon dioxide that certainly are 

 present in the escaping gas, when the liquid substance comes 

 in contact with the aperture and issue-valve, as this is opened. 

 I found, what I have not seen mentioned anywhere else, that 

 the solid carbon dioxide itself is a substance having a great 

 propensity to become electric, as the following experiments 

 show. 



When the snow-like solid matter, after it has been taken 

 from the receiving-bag, is put directly on the plate of the 

 electroscope, a strong charge of negative electricity is at once 

 apparent ; on placing this instrument under the receiver of 

 an air-pump, the divergence of the leaves rather diminishes 

 when the air is rarefied, and it increases again on admitting 

 air. A disk, formed by strongly compressing carbon dioxide 

 as indicated before, when rubbed with the hands or pressed 

 against the skin becomes negatively electrified and attracts 

 an electric pendulum in a very marked way, even when the 



* Wiedemann's Annalen, 1892, xlvii. p. 529. 



t Faraday examined air and vapour of water mixed with different sub- 

 stances, and expressed the opinion that when pure they fail to produce 

 electricity ; otherwise they communicate a positive charge to the electro- 

 scope when it is near to the exit valve, the gas then striking violently 

 against the knob of the instrument. At some distance below he states 

 that this becomes charged negatively, because it acts only as a receiver 

 to the gas already electrified on escaping, whilst in the former case 

 the knob of the electroscope is itself directly electrified by the collision 

 of the gas particles. 



G2 



