“It ought not to interfere with truth and justice; but I will not moralise nor complain. Iodine is as useful an ally to me as I could have found at home.” At Florence he worked in the laboratory of the Accademia del Cimento on iodine and on the diamond. The results of his work on iodine he embodied in a paper read to the Royal Society on June 16th, 1814, which deals mainly with the iodates, or, as he preferred to call them, the _oxyiodes_. The object of his work on the diamond was to determine whether any peculiar matter separated from it during its combustion, and whether the gas formed in the process was precisely the same in its chemical nature as that produced by the combustion of plumbago and charcoal. At Florence he made use of the great burning-glass originally employed in the trials on the action of solar heat on the diamond instituted by Cosmo III., Grand Duke of Tuscany; he completed the research in the laboratory of the Accademia dei Lincei at Rome. From the results of his different experiments, which were communicated to the Royal Society on June 23rd, 1814, it appeared that the diamond affords no other substance by its combustion in oxygen than pure carbonic acid gas, and that the only chemical difference perceptible between diamond and the purest charcoal is that the latter contains a minute proportion of hydrogen. “But,” he asks, “can a quantity of an element, less in some cases than 1/50000 part of the weight of the substance, occasion so great a difference in physical and chemical characters?” This he concludes is most unlikely, for, as he points out, even when the minute quantity of hydrogen is expelled by heating the charcoal in chlorine, the specific differences remain. The doctrine at that time current, and which seemed indeed almost axiomatic, “That bodies cannot be exactly the same in composition or chemical nature, and yet totally different in all their physical properties,” received its first great shock. Davy’s work, no doubt, paved the way for the recognition of the fact of allotropy, and thereafter of isomerism. In May he went to Naples and made his first ascent of Vesuvius, which he revisited on several subsequent journeys. He commissioned one of the guides to inform him from time to time of the condition of the volcano, and the man’s letters, in spite of their phonetic address--“Siromfredevi-Londra”--duly found their way to Albemarle Street. He also interested himself in the excavations at Pompeii instituted by direction of Murat, then King of Naples, and he performed a number of experiments on the colours used by the ancients in painting, an account of which was communicated to the Royal Society on February 23rd, 1815. He then passed northwards with the intention of spending the summer at Geneva. On his way he called at Milan to pay his respects to Volta. Of this visit he wrote:--