“The more the properties of the amalgam obtained from ammonia are considered the more extraordinary do they appear. Mercury by combination with about 1/12000 part of its weight of new matter is rendered a solid, yet has its specific gravity diminished from 13·5 to 3, and it retains all its metallic characters; its colour, lustre, opacity, and conducting powers remaining unimpaired. It is scarcely possible to conceive that a substance which forms with mercury so perfect an amalgam, should not be metallic in its own nature; and on this idea to assist the discussion concerning it, it may be conveniently termed ammonium.” Davy’s term “ammonium” is still retained in chemical nomenclature, but there is at present no evidence for the independent existence of such an entity; the so-called ammonium amalgam is certainly no proof. On December 15th, 1808, he delivered his third Bakerian lecture. It was entitled “An Account of some new analytical Researches on the Nature of certain Bodies, particularly the Alkalies, Phosphorus, Sulphur, Carbonaceous Matter, and the Acids hitherto undecompounded, with some general Observations on Chemical Theory.” Although this is one of the longest and most laboured of Davy’s papers, it is, perhaps, one of the least satisfactory. It is a record of many experiments with few definite results. Few as these were, they yet paved the way for consequences of the greatest importance. Gay Lussac and Thenard, on the publication of Davy’s second Bakerian lecture, succeeded in devising a method by which larger quantities of potassium might be obtained than by the electrolytic process. It consisted in passing molten potash over heated metallic iron and condensing the volatilised potassium in naphtha. On heating potassium in ammonia, they found that hydrogen was obtained together with potash, whence they concluded that potassium was a _hydruret of potash_. This experiment was repeated by Davy; he observed the formation of a substance since known as _potassamide_, and completely disproved the conjecture of the French chemists. His experiments on sulphur, phosphorus, and the various forms of carbon were, however, wholly fallacious, and his conclusions as to the non-elementary nature of these substances were erroneous, and were subsequently corrected by him. His work on the decomposition of boracic acid is, however, accurate, and he has every right to be considered as an independent discoverer, with Thenard, of the element subsequently called by him _boron_. At first Davy was inclined “to consider the boracic basis as metallic in its nature,” and to propose for it the name of _boracium_. His experiments with “fluoric acid” were vitiated by the circumstance that he worked with a mixture of hydrofluoric acid and silicon fluoride. Unwittingly he obtained small quantities of silicon, although he failed to recognise the individuality of this substance.