It is not the least surprising circumstance in the history of this system, that with such a blind and idolatrous admiration of its principles, so few facts should have been distorted. It is true that, from the belief that combustion could never take place without the presence of oxygen, the elementary principle of Scheele became, according to these views, a compound of oxygen and an acid; and the name of dephlogisticated marine acid was exchanged for that of oxy-muriatic acid, a circumstance which spread a cloud of error over the science, and perhaps retarded its progress in a greater degree than is generally imagined. In like manner, the chemist neglected to avail himself of the hint which, under other impressions, would have proved an important clue to discovery, viz. the acid properties of sulphuretted hydrogen.
We have now arrived at that stage in our history, when it may with propriety and advantage be asked—What has Davy done in correcting error, or in advancing truth?
The answer to this question will be nothing more than a summary of those discoveries which have been successively investigated during the progress of the present work.
The new doctrines of chemistry were highly instrumental in encouraging more extended investigations into all the different productions of nature and art; and we may observe, that one of the first efforts of Sir Humphry Davy was to improve our knowledge of the nature and habitudes of the tanning and astringent principles of vegetables,—an enquiry which had been commenced by Seguin and Proust. In pursuing even the most beaten path, he was sure to discover objects of novelty. Look at his early experiments on the cane, and on the straw of wheat, barley, and hay, and we shall see how magically he raised from their ashes a new flower of knowledge. He soon, however, quitted the track of other experimentalists; although we learn from the whole tenor of his researches, that he could obey as well as he could command, and he could act in the ranks, although he more frequently appeared as a general in the field of science.
Sir Humphry Davy has observed, that "at the time when the anti-phlogistic theory was established, electricity had little or no relation to chemistry. The grand results of Franklin respecting the cause of lightning, had led many philosophers to conjecture, that certain chemical changes in the atmosphere might be connected with electrical phenomena; and electrical discharges had been employed by Cavendish, Priestley, and Van-Marum, for decomposing and igniting bodies; but it was not till the era of the wonderful discovery of Volta, in 1800, of a new electrical apparatus, that any great progress was made in chemical investigation by means of electrical combinations.
"Nothing tends so much to the advancement of knowledge as the application of a new instrument. The native intellectual powers of men in different times are not so much the causes of the different success of their labours, as the peculiar nature of the means and artificial resources in their possession. Independent of vessels of glass, there could have been no accurate manipulations in common chemistry: the air-pump was necessary for the investigation of the properties of gaseous matter; and without the Voltaic apparatus, there was no possibility of examining the relations of electrical polarities to chemical attractions."
There is a candour in this statement which we cannot but admire. Nor does the admission diminish the glory of him who, by the application of such new instruments of research, was enabled to penetrate into the hidden mysteries of Nature. What avails the telescope, without the eye of the observer?
To Davy, the Voltaic apparatus was the golden branch, by which he subdued the spirits that had opposed the advance of former philosophers; but what would its possession have availed him, had not his genius, like the ancient Sibyl, pointed out its use and application?
It will be seen that he was thus enabled, not only to discover laws which are in constant operation, modifying the forms of matter, and influencing all the operations of chemistry, but, by applying them, to determine the elements of the fixed alkalies to be oxygen and a metallic base: a fact obviously opposed to the idea of oxygen being the general principle of acidity; for here it was the principle of alkalinity, if it may be so expressed. This was shaking the corner-stone of the edifice, and his subsequent researches into the nature of oxy-muriatic acid may be said to have overthrown it; for if either of the elements of this body can be considered as the acidifier, it is hydrogen. The consequences which flowed from this truth were of the highest importance, not only in correcting errors, which the progress of discovery, instead of rectifying, was actually multiplying, but in leading to the developement of new bodies. Iodine might have been recognised as an elementary body; but its relations to oxygen and hydrogen would probably have remained unknown, had not a knowledge of the true character of chlorine assisted the enquiry.
The same observation will apply to the recently discovered body, Bromine. In like manner has the chemist been led, by the chloridic theory, to a more accurate acquaintance with the composition of the fluoric, hydriodic, and hydrocyanic acids; while he has also learnt that hydrogen alone can convert certain undecompounded bases into well characterised acids, without the aid of oxygen. The same discovery has completely changed all our opinions with regard to a very important series of saline combinations, and developed the existence of new compounds of a most interesting description.