On This Day …….

What’s in water ? Well everyone knows it’s a compound containing hydrogen and oxygen. But of course that was not always the case, in fact water was considered one of the four elements in ancient Greek philosophy. So how did we come to realise that water was a compound and not an element, and how did we learn what it was composed off ? On the RSC ‘On This Day in Chemistry’ website  it reports today that on 15 January 1784, the scientist Henry Cavendish announced the composition of water to the Royal Society.  He presented the results of experiments where he had burned dephlogisticated air (oxygen) and inflammable air ( hydrogen) together observing a dew had formed on the apparatus. The inflammable air was produced by reacting acid with a metal which of course is how we produce hydrogen in our practical classes today. With further experiments he discovered that twice as much hydrogen is required than oxygen.


Cavendish was not alone on working on experiments to produce water, Joseph Priestley had also observed water in experiments (using ordinary air instead of oxygen) and Antonine Lavoisier also claimed to have discovered water. James Watt was Cavendish’s most serious contender for the discovery. Watt, a Scottish engineer, had a passion for steam engines and in his investigations to make them more efficient he also claimed to have discovered the composition of water. Cavendish was seen as a chemist whereas Watt was considered more of an inventor so two camps formed with their supporters and the ‘Water Controversy’ began. Interestingly,  the debate centred around the fact that Watt had established the concept of water as a compound before Cavendish produced the experimental data. Cavendish, who was always slow to publish due to his crippling shyness, eventually won the battle as later studies of his notebooks attributed the discovery to him.

Henry Cavendish Portrait

Cavendish was a complex individual who had great problems with social interaction which some now believe may have been autism. As with scientists of his time Cavendish worked in other fields such as electricity, the density of the Earth and even thermodynamics (James Watt also patented an idea that could be seen as the fore runner to the photocopier and also coined the term ‘horsepower’). At that time there was not the clear division between physics and chemistry that is seen today – a relative later donated funds for the Cavendish laboratories at Cambridge university. These are found in the Physics department and are probably one of the most famous sets of labs in the world producing a host of Nobel prize winners including Thompson, Rutherford, Watson and Crick to name a few. Because Cavendish was concerned with science for understanding not for profit at the time he was considered a ‘gentleman of science’ and I think that is a fitting tribute



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