Humphry Davy, Poet and Philosopher

by T. E. Thorpe

The attempts made by Davy to decompose the alkaline earths by methods similar to those adopted in the case of potash or soda were not very successful, and it was only when he had received intimation from Berzelius that they might be procured in the form of amalgams by operating in contact with mercury that he obtained any decisive results. In no case, however, was he able to prepare a pure metal, and his description of the physical properties of the substances he actually procured is exceedingly meagre. He seems to have been satisfied for the moment in demonstrating that—

“The evidence for the composition of the alkaline earths is of the same kind as that for the composition of the common metallic oxides; and the principles of their decomposition are precisely similar, the inflammable matters in all cases separating at the negative surface in the voltaic circuit, and the oxygen at the positive surface.”

“These new substances will demand names; and on the same principles as I have named the bases of the fixed alkalies, potassium and sodium, I shall venture to denominate the metals from the alkaline earths barium, strontium, calcium and magnium; the last of these words is undoubtedly objectionable but magnesium has been already applied to metallic manganese [by Bergman] and would consequently have been an equivocal term.”

However, as he states in his “Elements of Chemical Philosophy,” “the candid criticisms of some philosophical friends” induced him to subsequently change the name to magnesium.

He next made “Inquiries Relative to the Decomposition of Alumine, Silex, Zircone, and Glucine,” but although he made a large number of trials, the results were equivocal.

“Had I been so fortunate,” he says, “as to have obtained more certain evidences on this subject, and to have procured the metallic substances I was in search of, I should have proposed for them the names of silicium, alumium, zirconium, and glucium.”

One of the most interesting sections of the paper relates to the production of a so-called amalgam from ammonia, first obtained by Berzelius and Pontin. This curious substance has been the subject of much investigation, and little doubt is now entertained that it is merely a mercurial froth, as first stated by Daniell—that is, mercury distended by ammonia and hydrogen gases. Davy, however, saw in it the proof of the presence of oxygen in ammonia, and of the existence of what he called “the compound basis” of ammonia. He says:—

“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. Nor were the experiments with muriatic acid more decisive. Incidentally he obtained the two chlorides of phosphorus, but for a time their true nature escaped him, although he gives a fairly accurate description of their main properties.

The paper, although containing an account of much experimental work, was evidently put together in haste; it would have been better for his reputation had he delayed its publication. He seems to have been conscious of its imperfections, and to have sought to strengthen his conclusions by new experiments which he gives in an appendix. These, so far from substantiating his views, increased his doubts, and it is remarkable how he misinterpreted the phenomena he observed. Thus in one series of experiments he obtained considerable quantities of the “alcohol of sulphur of Lampadius,” and attempted to ascertain its nature, but his preconceptions as to the non-elementary nature of carbon and sulphur prevented him from recognising that it is a sulphide of carbon.