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Carbon electric arc lamp.
Carbon electric arc lamp.
Soon after Alessandro Volta invented the electric pile (battery), the British chemist Humphry Davy investigated the relationship between electricity and chemistry. This is a classic example of the interplay between science and technology. Scientific investigation led to the invention of the battery, which provided a source of electric current that was then used in further scientific investigations. That in turn would lead to new technologies (see here), and so on. As has often proved to be the case, the availability of a new tool meant that a large number of similar experiments could be carried out to probe the nature of the material world.
Davy started out from the correct deduction that the electricity produced by a voltaic pile was a result of chemical interactions going on in the pile. So he turned things around by looking at what chemical reactions were stimulated when an electric current was passed through different substances. His key discovery was that in many cases the effect of the current is to break a compound down into its component parts, a process now known as electrolysis. This led to the discovery of ‘new’ elements, in particular metals.
Davy began studying ‘voltaic action’ in 1800, when he was based in Bristol, and soon confirmed the link between chemistry and electricity by passing an electric current through water. A wire connected to the positive end of a battery (later known as the anode) was dipped in one end of a tank of water, while a wire connected to the negative end of the battery (later known as the cathode) was dipped in the other end of the tank, so that an electric current flowed through the water. The effect of the current was to produce bubbles of oxygen at the anode and bubbles of hydrogen at the cathode – and, of course, Davy already knew that oxygen gas and hydrogen gas combined to make water. The water had been decomposed by electricity into its constituent parts.
Davy’s investigations of this phenomenon had to be put on hold, because in 1801 he moved to a new post at the Royal Institution (itself new) in London, and in 1802 he became Professor of Chemistry there. His duties kept him busy on other projects for a time, but in 1806 he carried out a series of 108 experiments involving electrolysis. The basic experimental setup was improved by attaching the two wires (anode and cathode) to metal plates or rods dipped into the substance being studied. Davy presented the results of his work in a lecture to the Royal Society later that year, and went on in 1807 to electrolyse molten salts. He produced potassium from caustic potash (now known as potassium hydroxide), and sodium from caustic soda (sodium hydroxide). The experiment itself was very simple. Potash is found in the ashes of burned plants, which Davy collected in a small crucible. When an electrical current was passed through the ashes in the same way as in the electrolysis of water, the potash got hot enough to melt, and pure potassium collected around the cathode. These two metals had not previously been differentiated by chemists, but Davy showed that in spite of their similarities they are different elements. All this work was so important that Davy was awarded a French prize of 3,000 francs for the year’s best work on galvanic electricity, even though Britain and France were at war.
In further experiments (really, the same experiment repeated with different substances), Davy isolated magnesium, calcium, strontium, and barium. In a slight deviation from this work, in 1809 he made, or discovered, another use for electricity when he took the two wires from a battery and connected them to the opposite ends of a strip of charcoal. The electric current passing through the charcoal heated it until it glowed; Davy had invented the electric light, in the form of an arc lamp. This was essentially the end of his experimental research on electricity, although he did many other things (including isolating and naming the gas chlorine gas). In 1812, his achievements were marked by a high honour – he was knighted. This has more than personal significance, and is a landmark in the history of science. Davy was the first person in Britain to be knighted for his scientific work (Isaac Newton got his knighthood for political reasons), which indicates the increasing importance of science in early nineteenth-century society.