Re: Who was the first person to discover hydrogen and how did they discover it?

G'day Alex.

Henry Cavendish is indeed usually recognized as the discoverer of hydrogen, in about the year 
1766. But he wasn't "looking for" hydrogen, and he did not really know that it was hydrogen that 
he had discovered.

In the 1700s, nobody knew about gases. They knew about air, and they knew there were different 
types of air or "airs". They knew, for example, that the air in coal mines could cause explosions (we 
would now call it methane gas), or that the air from burning a fire in a tightly sealed room could 
kill you (carbon monoxide gas), or that breathing bad air could cause fevers and make you very 
sick (yes, 'malaria' is Latin or Italian for 'bad air')!

At this time the main people who were doing scientific investigations of gases -- 'airs' -- were a 
group of British chemists (often known as the 'pneumatic chemists'). Along with Cavendish, Joseph 
Priestley (co-discoverer of oxygen) and Joseph Black (discoverer of carbon dioxide), were among 
the best known of this group.

Let me hasten to add that there were also chemists working on gases and making important 
discoveries in Germany and Sweden. But the French, who at this time were the leaders in most of 
chemistry, were a little behind on the study of gases.

When we think of gases, we think of atoms and molecules. But the modern idea of atoms and 
molecules only started with Dalton in 1806, and was not understood in anything like the modern 
sense until about the 1850s.

Even without atoms and molecules, modern notions of elements and compounds, and which 
substances contained which elements, really only started with Lavoisier, the French chemist, in the 
1780s, several years after Cavendish's discovery. Not only that, but the pneumatic chemists mostly 
based their understandings of the different 'airs' they were producing and describing on the 
phlogiston theory (look up 'phlogiston' on the MadSci search engine, and in a web search). So they 
were on the opposite side to Lavoisier in a debate that was going on at that time about the nature 
of chemical substances. Eventually Lavoisier's view prevailed, and formed the basis that was 
gradually transformed into our modern understandings of chemical substances.

So Cavendish produced hydrogen by reacting iron with sulfuric acid, collecting the gas that formed 
over water, and measuring and weighing the gas to determine its density. He called it "flammable 
air" or, later, "light flammable air", because several other gases that burn readily were discovered. 
Similarly, Black called carbon dioxide "fixed air", and Priestley called oxygen "dephlogisticated air".

According to Encyclopaedia Britannica, Paracelsus had actually observed a flammable gas being 
given off from the reaction between iron and acid in the 1500s, but Cavendish was the first to 
collect the gas and try to get a good look at its properties. The gas that Paracelsus observed was 
later confused by others with methane, carbon monoxide, and acetylene, all of which are 
flammable and can be fairly readily made by simple chemical reactions.

The first way that hydrogen was made was in the reaction of metals with acids. By the 1880s it was 
also made by reacting steam with red hot iron.

Apart from Encyclopaedia Britannica, a good reference for this material is 'Science as Public 
Culture' by Jan Golinski, Cambridge University Press, 1992. It is a fascinating read, but rather 
heavy going at times, and probably a bit hard for someone at your level.