“The vivid combustion of bodies in oxymuriatic acid gas, at first view, appears a reason why oxygen should be admitted in it; but heat and light are merely results of the intense agency of combination. Sulphur and metals, alkaline earths and acids become ignited during their mutual agency; and such an effect might be expected in an operation so rapid as that of oxymuriatic acid upon metals and inflammable bodies.”
“That the quantity of hydrogen evolved during the decomposition of muriatic acid gas by metals, is the same that would be produced during the decomposition of water by the same bodies, appears, at first view, an evidence in favour of the existence of water in muriatic acid gas; but as there is only one known combination of hydrogen with oxymuriatic acid, one quantity must always be separated. Hydrogen is disengaged from its oxymuriatic combination by a metal, in the same manner as one metal is disengaged by another from similar combinations.”
He once more shows that by the strongest analytical power he can command oxymuriatic acid fails to yield any substance differing from itself:
“I have caused strong explosions from an electrical jar, to pass through oxymuriatic gas, by means of points of platina, for several hours in succession; but it seemed not to undergo the slightest change.”
Such, then, are the reasons which induced Davy to consider that oxymuriatic acid contains no oxygen; that it had hitherto been “undecompounded,” and that, therefore, by the strict logic of chemistry, it was to be regarded as an elementary body. Had his paper concluded at this point, his position would have been unassailable, even in the light of nearly ninety years of subsequent work. But he could not stop here. Berthollet, the author of the prevailing theory, had discovered a salt then known as hyper-oxymuriate of potash, presumably capable of furnishing an acid termed by Chenevix hyper-oxygenised muriatic acid. This salt is now termed potassium chlorate, after the acid which Davy subsequently succeeded in isolating, and which, when the chlorine theory was generally accepted, was called chloric acid by Gay Lussac. The existence of the hyper-oxymuriate of potash was for a time a stumbling-block, and Davy sought to explain it on the assumption that it was nothing more than a triple compound of oxymuriatic acid, potassium, and oxygen.
“We have no right to assume the existence of any peculiar acid in it, or of a considerable portion of combined water; and it is perhaps more conformable to the analogy of chemistry to suppose the large quantity of oxygen combined with the potassium, which we know has an intense affinity for oxygen, and which from some experiments, I am inclined to believe, is capable of combining directly with more oxygen than exists in potash, than with the oxymuriatic acid which, as far as is known, has no affinity for that substance.”
It is perfectly true, as Davy surmised, that potassium can combine with more oxygen than is contained in potash, but it is no less true, as he himself proved by his discovery of the so-called euchlorine, that chlorine can combine with oxygen. Although he made several attempts to isolate Mr. Chenevix’s hyper-oxygenised muriatic acid, he was not successful at the time, and was evidently disposed to doubt its separate existence.
The remaining portion of the paper, although of interest as exemplifying Davy’s power of dealing with the broad issues which his views raise, need not detain us now. He seizes the opportunity, however, to correct his statements with regard to the presumed compound nature of sulphur and phosphorus, and gives details of observations, some of which, as in other of his papers, have been “discovered” by subsequent observers. Thus he states:—
“I have never been able to burn sulphur in oxygen without forming sulphuric acid in small quantities; but in several experiments I have obtained from 92 to 98 parts of sulphurous acid from 100 of oxygen in volume; from which I am inclined to believe that sulphurous acid consists of sulphur dissolved in an equal volume of oxygen.”
It was hardly to be expected that views so entirely opposed to the convictions of chemists at the time should pass unchallenged. Berzelius, the countryman of Scheele, warmly defended the doctrine of the French School, and yet another Scotch professor sought to show that Davy was still “vera troublesome.” The controversy, in which Davy himself took little part, occasioned considerable stir at the period, and was even of interest outside philosophical circles. The discussion was not without its uses, inasmuch as it led to fresh discoveries. The noise of it all, however, is now forgotten. Berzelius eventually enjoined his cook to speak no longer of oxymuriatic acid: “Thou must call it chlorine, Anna; that is better.” Dr. Murray, with the pertinacity of his race, still clung to the old doctrine, and defended it with no little dialectical subtlety, but he alone was faithful among the faithless. It is true there has been an occasional flutter in the dovecots since these times, and the faith of chemists in the validity of Davy’s teaching has been once or twice assailed, but as yet it has survived all assaults.