Pray tell me that you are well; and remember me to all that are interested in me. My wife desires her kind remembrances. I am, my dear Underwood,
Your very sincere friend,
H. Davy.
Besides researches on the Torpedo, Davy made farther experiments on the ashes of Sea-weed, which were collected for him by Professor Viviani, of Genoa.
He left Genoa by water on the 13th, and arrived at Florence on the 16th of March. Here he worked in the laboratory of the Academia del Cimento, on Iodine; but more particularly on the combustion of the Diamond. The experiments on this latter body were performed by means of the great lens in the cabinet of Natural History; the same instrument as that employed in the first trials on the action of the solar heat on the diamond, instituted by Cosmo III. Grand Duke of Tuscany: upon this occasion, he was assisted by Count Bardi, the Director, and Signior Gazzari, the Professor of Chemistry at the Florentine Museum.
I have been informed that the hasty, and apparently careless manner in which he conducted his experiments, and which has been already noticed[10] as being characteristic of his style of manipulation, greatly astonished the philosophers of Florence, and even excited their alarm for the safety of the lens, which on all occasions had been used by them with such fastidious caution and delicacy.
In the very first trials on the combustion of the diamond, he ascertained a very curious circumstance that had not been before noticed; namely, that the diamond, when strongly ignited by the lens in a thin capsule of platinum, perforated with many orifices, so as to admit a free circulation of air, will continue to burn in oxygen gas after being withdrawn from the focus. The knowledge of this circumstance enabled him to adopt a very simple apparatus and mode of operation in his researches, and to complete in a few minutes experiments which had been supposed to require the presence of a bright sunshine for many hours.
The new facts obtained by the experiments on Iodine, which he had commenced at Montpellier and carried on at Florence, he embodied in a memoir, which was read before the Royal Society on the 16th of June 1814. It treated more particularly of the triple compounds containing iodine and oxygen,—of the hydrionic acid, and of the compounds procured by means of it,—of the combinations of iodine and chlorine,—of the action of some compound gases on iodine,[11]—and, lastly, of the mode of detecting iodine in combinations. "If iodine," he says, "exists in sea water, which there is every reason to believe must be the case, though in extremely minute quantities, it is probably in triple union with oxygen and sodium, and in this case it must separate with the first crystals of common salt."
He quitted Florence on the 3rd, and having visited Sienna, entered Rome on the 6th of April. The Continent having now become accessible, he met with many of his English friends: but neither the extended society by which he was surrounded, nor the classical attractions of the city of the Cæsars, allured him from the pursuits of Science. We find that, shortly after his arrival, he renewed his researches on the combustion of different kinds of charcoal, in the laboratory of the Academia del Lyncei, in which he was assisted by Sig. Morrichini and Barlocci, Professors of the College Sapienza at Rome. Having arranged the results of this investigation, together with those relating to the combustion of the diamond, which he had previously obtained at Florence, he transmitted a paper to the Royal Society, entitled "Some Experiments on the Combustion of the Diamond, and other carbonaceous substances;" which was read on the 23rd of June, and published in the Second Part of the Philosophical Transactions for the year 1814.
No sooner had it been established by various accurate experiments, that the diamond and common charcoal consumed nearly the same quantity of oxygen in combustion, and produced a gas having the same obvious qualities, than various conjectures were formed to explain the remarkable differences in the sensible qualities of these bodies, by supposing some minute difference in their chemical composition. MM. Biot and Arrago, from the high refractive power of the diamond, suspected that it might contain hydrogen. Guyton Morveau inferred from his experiments that it was pure carbon, and that charcoal was an oxide of carbon; whereas Davy was inclined to believe, from the circumstance of the non-conducting power of the diamond, as well as from the action of potassium upon it, that a minute portion of oxygen might enter its composition, although such a supposition would be at variance with the doctrine of definite proportions; but more lately, in his account of some new experiments on the fluoric compounds, he hazarded the idea that it might be the carbonaceous principle combined with some new and subtile element, belonging to the same class as oxygen, chlorine, and fluorine, which has hitherto escaped detection, but which may be expelled, or newly combined, during its combustion in oxygen. "That some chemical difference," says Davy, "must exist between the hardest and most beautiful of the gems and charcoal, between a nonconductor and a conductor of electricity, it is scarcely possible, notwithstanding the elaborate experiments that have been made on the subject, to doubt: and it seems reasonable to expect, that a very refined or perfect chemistry will confirm the analogies of Nature, and show that bodies cannot be exactly the same in composition or chemical nature, and yet totally different in all their physical properties."
With these impressions, we may readily imagine the ardour with which he availed himself of the use of the great lens at Florence. He had in various ways frequently attempted to fuse charcoal,[12] but without success. In a letter addressed to Mr. Children is the following passage: "The great result to be hoped for is the fusion of carbon; and then you may use diamond in the manufacture of gunpowder."