5. In the Memoirs of the Academy, for 1772 (published in 1776), are inserted two elaborate papers of Lavoisier, on the combustion of the diamond. The combustibility of the diamond was suspected by Newton, from its great refractive power. His suspicion was confirmed in 1694, by Cosmo III., Grand Duke of Tuscany, who employed Averani and Targioni to try the effect of powerful burning-glasses upon diamonds. They were completely dissipated by the heat. Many years after, the Emperor Francis I. caused various diamonds to be exposed to the heat of furnaces. They also were dissipated, without leaving any trace behind them. M. Darcet, professor of chemistry at the Royal College of Paris, being employed with Count Lauragais in a set of experiments on the manufacture of porcelain, took the opportunity of trying what effect the intense heat of the porcelain furnaces produced upon various bodies. Diamonds were not forgotten. He found that they were completely dissipated by the heat of the furnace, without leaving any traces behind them. Darcet found that a violent heat was not necessary to volatilize diamonds. The heat of an ordinary furnace was quite sufficient. In 1771 a diamond, belonging to M. Godefroi Villetaneuse, was exposed to a strong heat by Macquer. It was placed upon a cupel, and raised to a temperature high enough to melt copper. It was observed to be surrounded with a low red flame, and to be more intensely red than the cupel. In short, it exhibited unequivocal marks of undergoing real combustion. These experiments were soon after repeated by Lavoisier before a large company of men of rank and science. The real combustion of the diamond was established beyond doubt; and it was ascertained also, that if it be completely excluded from the air, it may be exposed to any temperature that can be raised in a furnace without undergoing any alteration. Hence it is clear that the diamond is not a volatile substance, and that it is dissipated by heat, not by being volatilized, but by being burnt. The object of Lavoisier in his experiments was to determine the nature of the substance into which the diamond was converted by burning. In the first part he gives as usual a history of every thing which had been done previous to his own experiments on the combustion of the diamond. In the second part we have the result of his own experiments upon the same subject. He placed diamonds on porcelain supports in glass jars standing inverted over water and over mercury; and filled with common air and with oxygen gas.[4] [4] The reader will bear in mind that though the memoir was inserted in the Mem. de l'Acad., for 1772, it was in fact published in 1776, and the experiments were made in 1775 and 1776.