“I have had another severe attack of inflammation in the eye, and was obliged to have the conjunctiva and cornea punctured. I suspect the cause was some little imperceptible fragment. I am just recovering, and hope I shall see as well soon as with the other eye.”
In the following April he was sufficiently recovered to resume the study of Dulong’s compound, and in a letter to Sir Joseph Banks, dated June 20th, 1813, and subsequently published in the Philosophical Transactions, he gives a number of details concerning its nature and composition. He accurately determined its specific gravity—viz. 1·653—but although he made a number of determinations of the amounts of its constituents by various methods, his deduction that it consisted of one proportion of nitrogen to four of chlorine was incorrect. The experiments of Gattermann, made with great skill and courage, have conclusively shown that the compound is, as long surmised, a trichloride of nitrogen.
At about the same period, as we learn from a letter to his brother, dated April 4th, 1813, he attacked the chemistry of fluorine:—
“I am now quite recovered, and Jane [Lady Davy] is very well, and we have both enjoyed the last month in London. I have been hard at work. I have expelled fluorine from fluate of lead, fluate of silver, and fluate of soda by chlorine. It is a new acidifier, forming three powerful acids; hydrofluoric, silicated fluoric, and fluo-boric. It has the most intense energies of combination of any known body, instantly combining with all metals, and decomposing glass. Like the fabled waters of the Styx, it cannot be preserved, not even in the ape’s hoof. We have now a triad of supporters of combustion.”
The results of Davy’s work were communicated to the Royal Society on July 8th, 1813. In his paper he states that M. Ampère of Paris had furnished him with many ingenious and original arguments in favour of the analogy between the muriatic and fluoric compounds, based partly upon his (Davy’s) views of the nature of chlorine, and partly upon reasonings drawn from the experiments of Gay Lussac and Thenard. After a short account of the main properties of the silicated fluoric acid gas (silicon fluoride), discovered by Scheele, fluoric acid (hydrofluoric acid), discovered by Scheele but first obtained pure by Gay Lussac and Thenard, and fluoric acid (boron fluoride), discovered by Gay Lussac and Thenard, he states that, on the hypothesis of M. Ampère—
“the silicated fluoric acid is conceived to consist of a peculiar undecompounded principle, analogous to chlorine and oxygen, united to the basis of silica, or silicum; the fluo-boric acid of the same principle united to boron; and the pure liquid fluoric acid as this principle united to hydrogen,”
He then seeks to put the hypothesis to the test of experiment by combining fluoric acid with ammonia in a platinum apparatus; the white solid substance he obtained—so-called fluate of ammonia—contained no moisture, and hence he inferred that no water was present and that therefore fluoric acid was free from oxygen. The inference was more correct than the experiment warranted. He further found that the action of potassium upon fluate of ammonia is precisely similar to its action upon muriate of ammonia, when ammonia and hydrogen are disengaged and muriate of potassa formed. He then attempted to electrolyse solutions of hydrofluoric acid. He says:
“I undertook the experiment of electrizing pure liquid fluoric acid, with considerable interest, as it seemed to offer the most probable method of ascertaining its real nature; but considerable difficulties occurred in executing the process. The liquid fluoric acid immediately destroys glass, and all animal and vegetable substances; it acts on all bodies containing metallic oxides; and I know of no substances which are not rapidly dissolved or decomposed by it except [certain] metals, charcoal, phosphorus, sulphur and certain combinations of chlorine.”
After various unsuccessful attempts to make tubes of sulphur and of the chlorides of lead and copper, he succeeded
“in boring a piece of horn-silver in such a manner that I was able to cement a platina wire into it by means of a spirit lamp, and by inverting this in a tray of platina filled with liquid fluoric acid, I contrived to submit the fluid to the agency of electricity.”