It was soon after observed by Henry, Haldane, Davy, and other experimenters, that other chemical compounds were decomposed by the electrical currents as well as water. Ammonia, for example, nitric acid, and various salts, were decomposed by it. In the year 1803 an important set of experiments was published by Berzelius and Hisinger. They decomposed eleven different salts, by exposing them to the action of a current of electricity. The salts were dissolved in water, and iron or silver wires from the two poles of the pile were plunged into the solution. In every one of these decompositions, the acid was deposited round the positive wire, and the base of the salt round the negative wire. When ammonia was decomposed by the action of galvanic electricity, the azotic gas separated from the positive wire, and the hydrogen gas from the negative.
But it was Davy that first completely elucidated the chemical decompositions produced by galvanic electricity, who first explained the laws by which these decompositions were regulated, and who employed galvanism as an instrument for decomposing various compounds, which had hitherto resisted all the efforts of chemists to reduce them to their elements. These discoveries threw a blaze of light upon the obscurest parts of chemistry, and secured for the author of them an immortal reputation.
Humphry Davy, to whom these splendid discoveries were owing, was born at Penzance, in Cornwall, in the year 1778. He displayed from his very infancy a spirit of research, and a brilliancy of fancy, which augured, even at that early period, what he was one day to be. When very young, he was bound apprentice to an apothecary in his native town. Even at that time, his scientific acquirements were so great, that they drew the attention of Mr. Davis Gilbert, the late distinguished president of the Royal Society. It was by his advice that he resolved to devote himself to chemistry, as the pursuit best calculated to procure him celebrity. About this time Mr. Gregory Watt, youngest son of the celebrated improver of the steam-engine, happening to be at Penzance, met with young Davy, and was delighted with the uncommon knowledge which he displayed, at the brilliancy of his fancy, and the great dexterity and ardour with which, under circumstances the most unfavourable, he was prosecuting his scientific investigations. These circumstances made an indelible impression on his mind, and led him to recommend Davy as the best person to superintend the Bristol Institution for trying the medicinal effects of the gases.
After the discovery of the different gases, and the investigation of their properties by Dr. Priestley, it occurred to various individuals, nearly about the same time, that the employment of certain gases, or at least of mixtures of certain gases, with common air in respiration, instead of common air, might be powerful means of curing diseases. Dr. Beddoes, at that time professor of chemistry at Oxford, was one of the keenest supporters of these opinions. Mr. Watt, of Birmingham, and Mr. Wedgewood, entertained similar sentiments. About the beginning of the present century, a sum of money was raised by subscription, to put these opinions to the test of experiment; and, as Dr. Beddoes had settled as a physician in Bristol, it was agreed upon that the experimental investigation should take place at Bristol. But Dr. Beddoes was not qualified to superintend an institution of the kind: it was necessary to procure a young man of zeal and genius, who would take such an interest in the investigation as would compensate for the badness of the apparatus and the defects of the arrangements. The greatest part of the money had been subscribed by Mr. Wedgewood and Mr. Watt: their influence of course would be greatest in recommending a proper superintendent. Gregory Watt thought of Mr. Davy, whom he had lately been so highly pleased with, and recommended him with much zeal to superintend the undertaking. This recommendation being seconded by that of Mr. Davis Gilbert, who was so well acquainted with the scientific acquirements and genius of Davy, proved successful, and Davy accordingly got the appointment. At Bristol he was employed about a year in investigating the effects of the gases when employed in respiration. But he did not by any means confine himself to this, which was the primary object of the institution; but investigated the properties and determined the composition of nitric acid, ammonia, protoxide of azote and deutoxide of azote. The fruit of his investigations was published in 1800, in a volume entitled, "Researches, Chemical and Philosophical; chiefly concerning Nitrous Oxide, or Dephlogisticated Nitrous Air, and its Respiration." This work gave him at once a high reputation as a chemist, and was really a wonderful performance, when the circumstances under which it was produced are taken into consideration. He had discovered the intoxicating effects which protoxide of azote (nitrous oxide) produces when breathed, and had tried their effects upon a great number of individuals. This fortunate discovery perhaps contributed more to his celebrity, and to his subsequent success, than all the sterling merit of the rest of his researches—so great is the effect of display upon the greater part of mankind.
A few years before, a philosophical institution had been established in London, under the auspices of Count Rumford, which had received the name of the Royal Institution. Lectures on chemistry and natural philosophy were delivered in this institution; a laboratory was provided, and a library established. The first professor appointed to this institution, Dr. Garnet, had been induced, in consequence of some disagreement between him and Count Rumford, to throw up his situation. Many candidates started for it; but Davy, in consequence of the celebrity which he had acquired by his researches, or perhaps by the intoxicating effects of protoxide of azote, which he had discovered, was, fortunately for the institution and for the reputation of England, preferred to them all. He was appointed professor of chemistry, and Dr. Thomas Young professor of natural philosophy, in the year 1801. Davy, either from the more popular nature of his subject, or from his greater oratorical powers, became at once a popular lecturer, and always lectured to a crowded room; while Dr. Young, though both a profound and clear lecturer, could scarcely command an audience of a dozen. It was here that Davy laboured with unwearied industry during eleven years, and acquired, by his discoveries the highest reputation of any chemist in Europe.
In 1811 he was knighted, and soon after married Mrs. Apreece, a widow lady, daughter of Mr. Ker, who had been secretary to Lord Rodney, and had made a fortune in the West Indies. He was soon after created a baronet. About this time he resigned his situation as professor of chemistry in the Royal Institution, and went to the continent. He remained for some years in France and Italy. In the year 1821, when Sir Joseph Banks died, a very considerable number of the fellows offered their votes to Dr. Wollaston; but he declined standing as a candidate for the president's chair. Sir Humphry Davy, on the other hand, was anxious to obtain that honourable situation, and was accordingly elected president by a very great majority of votes on the 30th of November, 1821. This honourable situation he filled about seven years; but his health declining, he was induced to resign in 1828, and to go to Italy. Here he continued till 1829, when feeling himself getting worse, and wishing to draw his last breath in his own country, he began to turn his way homewards; but at Geneva he felt himself so ill, that he was unable to proceed further: here he took to his bed, and here he died on the 29th of May, 1829.
It was his celebrated paper "On some chemical Agencies of Electricity," inserted in the Philosophical Transactions for 1807, that laid the foundation of the high reputation which he so deservedly acquired. I consider this paper not merely as the best of all his own productions, but as the finest and completest specimen of inductive reasoning which appeared during the age in which he lived. It had been already observed, that when two platinum wires from the two poles of a galvanic pile are plunged each into a vessel of water, and the two vessels united by means of wet asbestos, or any other conducting substance, an acid appeared round the positive wire and an alkali round the negative wire. The alkali was said by some to be soda, by others to be ammonia. The acid was variously stated to be nitric acid, muriatic acid, or even chlorine. Davy demonstrated, by decisive experiments, that in all cases the acid and alkali are derived from the decomposition of some salt contained either in the water or in the vessel containing the water. Most commonly the salt decomposed is common salt, because it exists in water and in agate, basalt, and various other stony bodies, which he employed as vessels. When the same agate cup was used in successive experiments, the quantity of acid and alkali evolved diminished each time, and at last no appreciable quantity could be perceived. When glass vessels were used, soda was disengaged at the expense of the glass, which was sensibly corroded. When the water into which the wires were dipped was perfectly pure, and when the vessel containing it was free from every trace of saline matter, no acid or alkali made its appearance, and nothing was evolved except the constituents of water, namely, oxygen and hydrogen; the oxygen appearing round the positive wire, and the hydrogen round the negative wire.
When a salt was put into the vessel in which the positive wire dipped, the vessel into which the negative wire dipped being filled with pure water, and the two vessels being united by means of a slip of moistened asbestos, the acid of the salt made its appearance round the positive wire, and the alkali round the negative wire, before it could be detected in the intermediate space; but if an intermediate vessel, containing a substance for which the alkali has a strong affinity, be placed between these two vessels, the whole being united by means of slips of asbestos, then great part, or even the whole of the alkali, was stopped in this intermediate vessel. Thus, if the salt was nitrate of barytes, and sulphuric acid was placed in the intermediate vessel, much sulphate of barytes was deposited in the intermediate vessel, and very little or even no barytes made its appearance round the negative wire. Upon this subject a most minute, extensive, and satisfactory series of experiments was made by Davy, leaving no doubt whatever of the accuracy of the fact.
The conclusions which he drew from these experiments are, that all substances which have a chemical affinity for each other, are in different states of electricity, and that the degree of affinity is proportional to the intensity of these opposite states. When such a compound body is placed in contact with the poles of a galvanic battery, the positive pole attracts the constituent, which is negative, and repels the positive. The negative acts in the opposite way, attracting the positive constituent and repelling the negative. The more powerful the battery, the greater is the force of these attractions and repulsions. We may, therefore, by increasing the energy of a battery sufficiently, enable it to decompose any compound whatever, the negative constituent being attracted by the positive pole, and the positive constituent by the negative pole. Oxygen, chlorine, bromine, iodine, cyanogen, and acids, are negative bodies; for they always appear round the positive pole of the battery, and are therefore attracted to it: while hydrogen, azote, carbon, selenium, metals, alkalies, earths, and oxide bases, are deposited round the negative pole, and consequently are positive.
According to this view of the subject, chemical affinity is merely a case of the attractions exerted by bodies in different states of electricity. Volta first broached the idea, that every body possesses naturally a certain state of electricity. Davy went a step further, and concluded, that the attractions which exist between the atoms of different bodies are merely the consequence of these different states of electricity. The proof of this opinion is founded on the fact, that if we present to a compound, sufficiently strong electrical poles, it will be separated into its constituents, and one of these constituents will invariably make its way to the positive and the other to the negative pole. Now bodies in a state of electrical excitement always attract those that are in the opposite state.