Can some one tell me what can detect the accurate gas electric conductivity? Can someone tell me how and what kind of gas could conduct electricity and what instrument could detect it?
 A: Under normal conditions, gases do not conduct electricity, since gas molecules are neutral. 
To make a gas conduct electricity, gas molecules have to be ionized, i.e., split into positive and negative ions. 
The ionization of gas can occur, for instance, if a very high voltage is applied between two electrodes and some electrons escape from the negative electrode, speed up and collide with gas molecules, present in the gap between the electrodes, splitting them into positive and negative ions. The newly created ions, in turn, speed up and ionize more gas molecules, making the gas more and more conductive.
The conductivity of the ionized gas can be estimated by measuring the current in the circuit containing the gap.  
A: The detection of electric current, can be done by Galvanometer. 
In order to conduct electricity, charges must be present. The gas can accept foreign charges or we can ionise the gas at high temperatures or pressure. Apply electric field and you have moving charges which gives current.
Galvanometer is present outside the circuit. Check Cathode Ray Experiment
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