Many of the well-waters contain gases; thus the town of Roma is lighted by natural gas which escapes from its well.
They have made this observation the basis of a practical method of separating helium from the other inert gases.
They involve high cost in fuel and labour, but permit the utilization of the waste gases.
This phenomenon is connected with the fact that incandescent bodies, especially in rarefied gases, throw off or emit electrons or gaseous negative ions.
Dalton, who was a mathematical physicist even more than a chemist, had given much thought to the study of gases.
