CHAPTER XIV 



HYDROGEN 



UP to the middle of the eighteenth century several gases were 

 known which were confused together under the general name 

 "inflammable air." But in 1766 Henry Cavendish, in a paper 

 on " Factitious Air," showed that the gas which is procured by 

 the action of diluted sulphuric or muriatic acid on zinc and iron 

 is to be distinguished from the inflammable air known as marsh- 

 gas, and the other variety obtained by passing air over or through 

 red-hot charcoal. He afterwards proved that this kind of 

 " inflammable air " unites with half its volume of " dephlogisti- 

 cated air " (oxygen) to form water. 



The inflammability of the gas coupled with its extraordinary 

 lightness led the discoverer and others to suppose that it was 

 actually " phlogiston " itself, the then assumed hypothetical 

 principle of combustibility. The name hydrogen, which means 

 water producer, was given to the gas by Lavoisier, in accordance 

 with the system of nomenclature contrived by him some years 

 later. The lightness of the gas always excited curiosity, and 

 after the phlogistic theory had been abandoned and phlogiston 

 a thing of the past, the idea arose that hydrogen was in fact a 

 realisation of the notion which had come down from ancient 

 times as to the existence of a Trpwrrj v\t] or protyl, the primal 

 matter out of which all else was composed. 



These speculations are now merely matters for antiquarian 

 curiosity, but the fact still remains that of all forms of matter 

 known to the chemist hydrogen is the lightest. Standing next 

 to it is the rare gas helium, which is just twice as heavy bulk for 

 bulk, and the next in order is methane or marsh-gas, CH 4 , which 

 is eight times as heavy as hydrogen. 



The development of the balloon into the airship is one and 

 perhaps the chief reason for enquiry into the methods by which 

 hydrogen may be manufactured in quantity. Formerly aero- 

 nauts were content with charging their balloons with an impure 

 kind of methane, obtained by distilling coal at a relatively high 

 temperature, and collecting the last portions of the gas escaping 

 from the retort. 



