In addition to the observations of Sir William Hamilton, Bergmann, Formes, and Dalhieu, on the composition of different lavas, which have been given in the Encyclopedia, we cannot refuse ourselves the pleasure of noticing, in this place, those of Sir James Hall. From a number of well-devised experiments, Sir James thinks himself warranted to conclude, that lava and whitestone are intrinsically the same substance; and that their apparent differences arise wholly from the circumstances under which they have passed from a liquid to a solid state. The lavas, it is well known, have been cooled rapidly in the open air, and the whites (according to Dr Hutton's theory, which Sir James seems willing to adopt) slowly in the bowels of the earth.

Though we are far from adopting that theory in all its parts, to which we think insuperable objections may be made (see Earth, Encycl. p. 120), we admit, that the experiments of Sir James Hall go far to establish the identity of lava and whitestone. These experiments were made upon seven different species of whitestone and six lavas, of which four were broken from the currents of Etna and Vesuvius by Sir James himself. Each of the original whitestones was reduced, by fusion and subsequent rapid cooling, to a state of perfect glass. This glass, being again placed in the furnace, was subjected to a second fusion. The heat, being then reduced to a temperature generally about 28° of Wedgewood, was maintained stationary for some hours; when the crucible was either immediately removed, or allowed to cool with the furnace. The consequence was, that in every case the substance had lost the character of glass, and by crystallization had assumed in all respects that of an original whitestone. It must be owned, that in most cases the new production did not exactly resemble the particular original from which it was form- ed, but some other original of the same class; owing to accidental varieties in the mode of refrigeration, and to chemical changes which unavoidably took place during the process. In the case, however, of the rock of Edinburgh castle, and of that of the basaltic columns of Staffa, the artificial substances bear a complete resemblance to their originals, both in colour and texture.

The lavas were now treated in the same way, and were each, by fusion and rapid cooling, reduced, as the whitewashes had been, to glass. This glass, when fused again and cooled slowly, yielded the same kind of crystallized, flaky, or earthy masses, completely resembling an original whin or lava.

Although the internal structure of lava thus accounted for, yet Sir James was embarrassed with the state of its external surface; which, though cooled in contact with the open air, is seldom or never vitreous, holding an intermediate state between glass and stone; but this difficulty was removed by a circumstance which took place in the course of these experiments. It was found, that a small piece of glass of any of the lavas, or of several of the whins, being introduced into a muffle, the temperature of which was at any point between the 20th and the 22nd degree of Wedgwood's scale, the glass became quite soft in the space of one minute; but, being allowed to remain till the end of a second minute, it was found to have become hard throughout in consequence of a rapid crystallization, to have lost its character of glass, and to have become by 12 or 14 degrees more fusible, being unaffected by any heat under 30°, though the glass had been fusible at 18° or at 16°. This accounted for the scoria on the surface of lavas; for the substance even at the surface, being in contact with the flowing stream, and surrounded with heated air, could not cool with excessive rapidity: and the experiment shows, that should any part of the mass, in descending heat, employ more than one or two minutes in cooling from 22 to 20°, it would infallibly lose its vitreous character.

Independently of any allusion to system or to general theory, Sir James Hall flatters himself that these experiments may be of some importance, by simplifying the history of volcanoes; and, above all, by supposing some very extraordinary, and, he conceives, unphilosophical opinions advanced with regard to volcanic heat, which has been stated as possessing very little intensity, and as acting by some occult and inconceivable influence, or with the help of some invisible agent, so as to produce liquidity without fusion. These suppositions, which have been maintained ferociously by some of the most celebrated naturalists in Europe, have originated from the difficulty of accounting for the stony character of lavas when compared with that of glass, which they assume in consequence of fusion in our furnaces. But now he hopes we may be relieved from the necessity of such violent efforts of imagination, since the phenomena have been fully accounted for by the simple, though unnoticed, principle of refrigeration, and have been repeated again and again with ease and certainty in a small chamber furnace.

Lavoisier (Antoine Laurent), was born in Paris on the 26th of August 1743. His father, who directed his education, was opulent, and spared no cost for his improvement. The youth showed a decided taste for the physical sciences. In 1764, government having proposed an extraordinary premium for the best Lavoisier, and cheapest mode of lighting the streets of a large city, Lavoisier obtained the gold medal; and his memoir, full of nice investigation, was printed by the Academy. Into that body he was received on the 13th May 1768, in spite of a formidable opposition; and to its service he ever after devoted his labours, and became one of its most useful associates and coadjutors.

His attention was successively occupied with every branch of physical and mathematical science. The pretended conversion of water into earth, the analysis of gypsum in the neighbourhood of Paris, the crystallization of salts, the effects produced by the grande de loupe of the garden of the Infanta, the project of bringing water from l'Yvette to Paris, the congelation of water, and the phenomena of thunder and the aurora borealis—all occupied his attention.

Journeys, undertaken in concert with Guettard into every district of France, enabled him to procure numberless materials towards a description of the lithological and mineralogical empire; these he arranged into a kind of chart, which wanted little of being completed. They served also as a foundation for a more laborious work of his on the revolutions of the globe, and the formation of Couches de la Terre; a work of which two beautiful sketches are to be seen in the Memoirs of the French Academy for 1772 and 1787. All the fortune and all the time of Lavoisier were devoted to the culture of the sciences; nor did he seem to have a preponderating inclination for any one in particular, until an event, such as seldom occurs in the annals of the human mind, decided his choice, and attached him thenceforth exclusively to chemistry—a pursuit which has since rendered his name immortal.

The important discovery of gases was just announced to the philosophical world. Black, Priestley, Scheele, Cavendish, and Macbride, had opened to physiologists a sort of new creation; they had commenced a new era in the annals of genius, which was to become equally memorable with those of the compass, printing, electricity, &c.

It was about the year 1770 that Lavoisier struck with the importance and grandeur of this discovery, turned his attention to this inexhaustible fountain of truths, and instantly perceived, by a kind of instinct, the glorious career which lay before him, and the influence which this new science would necessarily have over the whole train of physical researches. Of those who had preceded him, the most indefatigable experimenter was Priestley; but facts the most brilliant remained frequently unproductive in his hands; on every occasion he was ready to frame some crude hypothesis, which as hastily he abandoned. Lavoisier was imbued with the true spirit of inductive philosophy; his observations, eminently precise and luminous, always pointed to general views. In 1774, he published his chemical opuscules, which contained a very neat history of all that had been done with respect to gases, and concluded with the author's capital experiments, by which it was proved, that metals, in calcination, derive their augmentation of weight from the absorption of air. Soon afterward, he showed, in opposition to Priestley, that nitrous acid is composed of air; a remark, of which the importance appeared in the sequel. His ingenuity as a chemist was now so well known, that in 1776 Turgot employed Lavoisier eft him to inspect the manufacture of gun-powder. He introduced some valuable improvements, and, suppressing the odious viti in quest of the materials of saltpetre, he yet quintupled its produce. The gunpowder would now carry 120 toises, when formerly it would not reach 90. This superiority was indeed acknowledged in the last war.

It had been alleged, that by frequent distillation water is converted into earth. This question Lavoisier resolved in 1778, having shewn that the earthy sediment was owing to the continual erosion of the internal surface of the retort. In that same year he made a more interesting discovery; namely, that the respirable portion of the atmosphere is a constituent principle of all acids, and which he therefore denominated oxygen; a most important fact, and the first great step towards the new chemistry; which the composition of water, ascertained in 1783, triumphantly completed.

Lavoisier possessed decisive advantages over his contemporaries; he studied a geometrical accuracy of investigation; and his wealth enabled him to make experiments on a large scale, and to use instruments of the most perfect construction. He was able to hold in his house, twice every week, assemblies, to which he invited every literary character that was most celebrated in geometrical, physical, and chemical studies; in these instructive conversations, discussions, not unlike such as preceded the first establishment of academies, regularly took place. Here the opinions of the most eminent literati in Europe were canvassed; passages the most striking and novel, out of foreign writers, were recited and unnoticed on; and theories were compared with experiments. Here learned men of all nations found easy admission; Priestley, Fontana, Blagden, Ingenhousz, Landriani, Jacquin, Watt, Bolton, and other illustrious physiologists and chemists of England, Germany, and Italy, found themselves mixed in the same company with La Place, La Grange, Borda, Cousin, Meunier, Vandermonde, Monge, Moreau, and Berthollet. Happy hours passed in these learned interviews, wherein no subject was left uninvestigated that could possibly contribute to the progress of the sciences, and the amelioration and happiness of man. One of the greatest benefits resulting from these assemblages, and the influence of which was soon afterwards felt in the academy itself, and consequently in all the physical and chemical works that have been published for the last twenty years in France, was the agreement established in the methods of reasoning between the natural philosophers and the geometricians. The precision, the severity of style, the philosophical method of the latter, was infensibly transfused into the minds of the former; the philosophers became disciplined in the tactics of the geometricians, and were gradually moulded into their resemblance.

It was in the assemblage of these talents that Lavoisier embellished and improved his own. When any new result from some important experiment presented itself, a result which threatened to influence the whole theory of the science, or which contradicted theories till then adopted, he repeated it before this select society. Many times successively he invited the severest objections of his critical friends; and it was not till after he had surmounted their objections, to the conviction and entire persuasion of the society; it was not till after he had removed from it all mystery and obscurity, that he ventured to announce to the world any discovery of his own.

At length he combined his philosophical views into a consistent body, which he published in 1789, under the title of Elements of Chemistry; a book which is a most beautiful model of scientific composition, clear, logical, and elegant. It would be foreign to our purpose to attempt an exposition of the principles, or to expatiate on the merits, of this celebrated system; which, within the space of a very few years, has been almost universally adopted, and which, if not the genuine interpretation of nature, approaches as near to it as the present state of knowledge will permit. See Chemistry in this Supplement.

The last, but not the least useful, of Lavoisier's philosophical researches, on the Perpiration of Animals, was read to the Academy on the 4th May 1791, and of which part was published in the volume for 1790. He found, by some delicate experiments, made in conjunction with Seguin, that a man in 24 hours perspires 45 ounces; that he consumes 33 ounces of vital air; that he discharges from the lungs 8 cubic feet of carbonic acid gas, of which one-third is carbon and two-thirds are oxygen; that the weight of water discharged from the lungs amounts to 23 ounces, of which 3 are hydrogen and 20 oxygen, exclusive of 6 ounces of water already formed, lost in pulmonary perspiration. These discoveries were directed to the improvement of medicine.

We have mentioned the assistance which Lavoisier received while he was digesting his new system of chemistry; but we must add, that to him pertains exclusively the honour of a founder. His own genius was his sole conductor, and the talents of his associates were chiefly useful in illustrating discoveries he himself had made; he first traced the plan of the revolution he had been a long time conceiving; and his colleagues had only to pursue and execute his ideas.

In the twenty volumes of the Academy of Sciences, from 1772 to 1793, are 40 memoirs of Lavoisier, replete with all the grand phenomena of the science; the doctrine of combustion, general and particular; the nature and analysis of atmospheric air; the formation and fixation of elastic fluids; the properties of the matter of heat; the composition of acids; the augmentation of the ponderosity of burnt bodies; the decomposition and recomposition of water; the distillation of metals; vegetation, fermentation, and animalization. For more than 15 years consecutive, Lavoisier pursued, with unshaken constancy, the route he had marked out for himself, without making a single false step, or suffering his ardour to be damped by the numerous and increasing obstacles which constantly beset him.

Many were the services rendered by Lavoisier, in a public and private capacity, to manufactures, to the sciences, and to artists. He was treasurer to the Academy after Buffon and Tillet, and introduced economy and order into the accounts. He was also a member of the Board of Consultation, and took an active share in whatever was going forwards. When the new system of measures was agitated, and it was proposed to determine a degree of the meridian, he made accurate experiments on the expansion of metals, and constructed a metallic thermometer. By the National Convention... Like a good citizen, Lavoisier turned his thoughts to political economy. Between the years 1778 and 1785, he allotted 240 arpents in the Vendômois to experimental agriculture, and increased the usual produce by one-half. In 1791, he was invited by the Constituent Assembly to digest a plan for simplifying the collection of the taxes. This gave occasion to an excellent report, afterwards printed with the title of *Territorial Riches of France*. At this time, also, he was appointed commissioner of the national treasury, in which he effected some beneficial reforms.

During the horrors of the Robespierrean dictatorship, Lavoisier told La Lande that he foresaw he should be stripped of his property, but that he would work for his bread. The profession of apothecary would have suited him best. But his doom was already fixed. On the 8th of May 1794, confounded with 28 farmers-general, he suffered on the scaffold, merely because he was rich!

Lavoisier was tall, and of a graceful, sprightly appearance. He was mild, sociable, obliging, and extremely active; and in his manners he was unaffectedly plain and simple. Many young men, not blessed with the gifts of fortune, but incited by their genius to woo the sciences, have confessed their obligations to him for pecuniary aid; many, also, were the unfortunate whom he relieved in silence, and without the ostentation of virtue. In the communes of the department of the Loir and Cher, where he possessed considerable estates, he would frequently visit the cottages of indigence and distress; and long will his memory be cherished there. But his reputation, influence, virtues, and wealth, gave him a great preponderance, which unfortunately provoked the jealousy of a crew of homicides, who made a sport of sacrificing the lives of the best of men to a fan-guineous idol.

This great and good man married, in 1771, Marie-Anne-Pierrette Paulze, daughter of a farmer-general; a woman whose wit and accomplishments constituted the charm of his life; who assisted him in his labours, and even engraved the figures of his last work.

**LEAD.** See that article (*Encycl.*), and Chemistry-Index in this Supplement. It is well known, that lead generally contains a portion of silver, and sometimes of gold; and that there are occasions, particularly in assaying, when it is of importance to have it freed from these metals. For accomplishing these purposes different processes have been proposed; but the following by Pet. Jac. Hjelm, as it is the least expensive, promises to be the most useful:

**LITHARGE** (see *Encycl.*) was the substance on which this chemist made his experiments, and his principal object was to free it from all mixture of silver. This was accomplished in the following manner: He placed a crucible, in which half a pound of litharge found good room, and which was fitted with a close cover, in a wind-furnace filled with dead coals. He then put into the crucible a mixture of four ounces of potash and the same quantity of powder of flint. When the whole was well melted by strengthening the draught, and making the coals glow, he took off the cover, and laid hold of the crucible with a pair of tongs, in order to take it out, and to suffer this very fusible glass to cover the inside of the crucible, to secure it from the glass of the lead which he meant to melt in it. The superfluous glass was poured out; the crucible again placed on its foot, and half a pound of litharge thrown into it with a shovel. The cover was placed upon it while the litharge was melting; and when it was thoroughly glowing and fluid, charcoal dust was sifted into the uncovered crucible through a sieve, so that the surface of the litharge was completely covered with it. This immediately produced an effervescence, and the rising of bubbles, by means of the separation of the air occasioned by the reduction of the lead. During this process, the cover was put on, and a few coals thrown into the furnace: when these were burnt, every thing in the crucible was quiet, and the melted mass was poured into a warm conical mould. The crucible was then again filled with half a pound of the same kind of litharge, and put into the furnace, and charcoal dust was several times sifted over the melted surface, till it was well covered before the mass was thrown out, a sufficient space being every time left for the effervescence. The first mass had, in the mean time, become cool, and, on examination, contained four ounces of lead at the bottom, and litharge at the top. When this litharge was reduced with potashes and wine stone, the lead thence obtained, which weighed 23 ounces, was found to contain less than one-half grain of silver in the pound. In the second mass there was found somewhat more than five ounces of lead, which contained all the silver that had been before mixed with the litharge, because in the lead which had been reduced from the litharge in the above manner, there were no perceptible traces of silver. This lead was then melted over a slow fire, and cast into bars, which were rolled smooth, and formed into masses of a known weight, to be used for assaying gold and silver, and for other purposes of the same kind. All these meltings were made in one crucible, which, according to every appearance, remained unhurt. If the same experiments were made with red lead, the like result would infallibly follow.

With the same view of obtaining lead free from silver, he melted, in the like manner, half a pound of white lead, which produced half an ounce of lead. When the litharge standing over it was revived, the lead obtained was still found to contain too much silver. He therefore precipitated another half pound of white lead by charcoal powder, after the lead that fell from it had been separated; and then it produced, by reviving, a mass of lead without any mixture of silver.