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two fixed alkalis both yielded in this process metallic bases; but that of potash had alone the quality of combustion at the temperature of 150°, and it was, though a metal, lighter than water in the proportion of 97 to 100. When thrown into water in the air, it detonates and burns with violence, forming a solution of potash. The metal from soda is still lighter, being to water as 86 to 100; but it does not so easily unite with oxygen, though it decomposes water with a hissing noise, and makes with it a solution of soda. To these metals the discoverer gave the name of potassium and sodium. The glory of having now made the greatest discovery of the age was plainly Davy's; and it was not the result of happy accident, but of laborious investigation, conducted with a skill and a patience equally admirable, and according to the strict rules of the soundest philosophy. He had indeed begun by discovering the laws of electrical action, and had thus formed the means of his new discovery, which was the fruit of the science he had founded, as Newton's theory of dynamics and of astronomy was the fruit of the calculus which he had so marvellously discovered when hardly arrived at man's estate.

The wonder excited by the strange bodies with which philosophers were thus brought acquainted, was of course in part owing to their novel and singular properties, which formed no part of the discoverer's merits, yet might be reckoned as the perquisites of his genius. His praise would have been the same if instead of at once discovering the alkalis to be oxides, and the metal forming the base to be one lighter than water, or bees'-wax or box-wood, and the other to burn unheated in the open air, he had only shown those salts to be oxides of well-known metals. Yet, as his investigation had been crowned with the discovery of strange substances, metallic, and yet like no other metals, we justly admire the more, and the more thank him for his double service rendered to science.

The long labour thus ending in so mighty a result, and the excitement naturally enough produced in an irritable habit, threw him into an illness of a most serious complexion. For many days he lay between life and death in a low nervous fever, and it was not till the following March that he could resume his inquiries into the composition of the alkaline earths. It is to the credit of chemists that no one deemed himself at liberty to interfere with him, as any one might now by only following his footsteps have done, and thus analysed these earthy bodies. He himself, early in the summer following his illness, had reduced lime, magnesia, strontites, and barytes. In these experiments he was greatly assisted by the ingenious contrivances which Gay-Lussac and Thenard had recently used for the reduction of the alkaline oxides. The metals thus discovered were not any wise light or fusible like potassium and sodium; but they burnt with a bright light on being exposed to considerable degrees of heat, and they decomposed water; and either by their combustion, or their exhibition to water, they reproduced the alkaline earths.

A number of other experimental researches led Davy to new and curious observations on the constitution and habits of different substances. But we need only mention the most important of these, for it was a discovery very unexpected both by himself and the chemical world at large. The acid hitherto called oxygenated muriatic, or oxymuriatic, on account of its powerful acid qualities, had been always from thence supposed to contain an excess of oxygen, believed to be the acidifying principle. At last Gay-Lussac and Thenard, in 1809, concluded from some experimental researches, or rather they suspected, that it might be a simple and elementary substance; but they on the whole still inclined to think it contained oxygen according to the old and received opinion. Davy now found, by a course of satisfactory experiments which have fixed the

opinions of all philosophers on the subject, that the suspicion of those eminent men was well founded; that the oxymuriatic acid is a simple substance, containing no oxygen, that it unites with oxygen to form an acid, which forms with alkalis the detonating salts hitherto called oxymuriates, as being supposed to contain oxymuriatic acid combined with alkaline bases; and finally, that with hydrogen it forms the acid long and well known as the muriatic or marine. To the oxymuriatic acid he gave the name of chlorine from its green colour, and to common muriatic acid that of hydrochlorine. The union of chlorine and oxygen he calls chlorine acid, and its compounds, of course, chlorates. This is justly reckoned one of the most important of Davy's many brilliant discoveries.

It remains to make mention of the valuable present which this great philosopher offered to humanity-his safety-lamp. The dreadful ravages made on human life by the fire-damp explosions—that is, the burning of hydrogen gas in mines-had often attracted the notice of both the mine-owner and the philanthropist. Various inventions had been fallen upon to give light in those recesses of the earth with so low a degree of heat as should be insufficient to explode the gas. One of them was a series of flints playing by machinery against each other so as to give a dim light; but this had very little success; it was clumsy, and it was not effectual so as to cause its use by miners. The ventilation of the galleries by furnaces and even by air-pumps was chiefly relied on as a preventive; but gas would collect in spite of all preventives, and the destruction of a hundred or more lives was not an unusual calamity. Davy about the year 1815 turned his attention to the subject, and after fully ascertaining that carburetted hydrogen is the cause of the fire-damp, and finding in what proportions it must be mixed with air in order to explode (between six and fourteen times its bulk), he was surprised to observe, in the course of his experi

ments made for the purpose of ascertaining how the inflammation takes place, that the flames will not pass through tubes of a certain length or smallness of bore. He then found that if the length be diminished, and the bore also reduced, the flames will not pass; and he further found that by multiplying the number of the tubes, their length may safely be diminished to hardly anything, provided their bore be proportionably lessened. Hence it appeared that gauze of wire, whose meshes were only one twenty-second of an inch diameter, stopped the flame, and prevented the explosion. The candle or lamp being wrapt in such gauze, and all access to the external air prevented except through the meshes, it is found that the lamp may be safely introduced into a gallery filled with fire-damp; a feeble blue flame will take place inside the gauze, but no explosion, even if the wire be heated nearly red.

The theory is, but it seems very questionable, that the conducting power of the wire carrying off the heat prevents a sufficient quantity reaching the explosive compound. Subsequent inquiries seem to prove that although in a still atmosphere of explosive gas the lamp is a perfect protection, yet it does not prevent a current of gas from penetrating to the flame and exploding. It is attempted to guard against this by interposing a tin shield or screen; but a current very often in mining operations arises before any notice can be given. Had Davy's life and health been prolonged, he might have further improved his invention so as to meet this objection. He certainly never was fully convinced of its force, as I know from having discussed the subject with him; and no doubt the testimony of so great an engineer as the late Mr. Buddle, given before a Parliamentary Committee to whom the examination of this important subject was referred, deserves great attention. He positively affirmed that "having seen 1000, and sometimes 1500 safety-lamps in daily use, and in all possible varieties of explosive mixtures, he had never

known one solitary instance of an explosion." As for the lamentable accidents which continue to happen, we can scarcely doubt that they originate in the dreadful carelessness of their own and of other men's lives, which seems to be engendered in those who are habitually exposed to great danger. That they themselves are the first to suffer for it, can only suppress the outward expression of the feelings which recklessness like this is fitted to produce.

It redounds to the credit of the north country mineowners that in 1817 they invited the inventor of the Lamp to a public entertainment, and presented him with a service of plate of two thousand pounds value. It must be remembered that he had generously given to the public the whole benefit of his invention, and thus sacrificed the ample profit which a patent must have enabled him to acquire for himself.

Davy had as early as 1806 been chosen a foreign associate of the French Institute. In 1812 he received from the Regent the honour of knighthood. About the same time he married Mrs. Apreece, a lady whose ample fortune was by far the least valuable part of her accomplishments—a person of great virtue, admirable talents, and extensive information. Of this marriage there has been no issue. In October, 1813, he published his 'Elements of Chemical Philosophy,'-a hasty and even somewhat crude work, but abounding, as whatever he wrote was sure to abound, in important and ingenious observations. In the following year appeared his Elements of Agricultural Chemistry,' of which the same general character may be given. In 1816 he was created a baronet.

Napoleon had, during the war, given him permission to visit the extinguished volcanoes in Dauvergne, and to pass through France towards Naples, Vesuvius being then in a state of eruption. His reception at Paris was very warm, but unfortunately he failed to retain the affection of his colleagues in the Institute.

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