The introduction of this chemical language can never cease to be considered one of the most important steps ever made in the improvement of technical terms; and as a signal instance of the advantages which may result from artifices apparently trivial, if employed in a manner conformable to the laws of phenomena, and systematically pursued. It was, however, proved that {276} this language, with all its merits, had some defects. The relations of elements in composition were discovered to be more numerous than the modes of expression which the terminations supplied. Besides the sulphurous and sulphuric acids, it appeared there were others; these were called the _hyposulphurous_ and _hyposulphuric_: but these names, though convenient, no longer implied, by their form, any definite relation. The compounds of Nitrogen and Oxygen are, in order, the _Protoxide_, the _Deutoxide_ or _Binoxide_; _Hyponitrous_ Acid, _Nitrous_ Acid, and _Nitric_ Acid. The nomenclature here ceases to be systematic. We have three oxides of Iron, of which we may call the first the _Protoxide_, but we cannot call the others the _Deutoxide_ and _Trioxide_, for by doing so we should convey a perfectly erroneous notion of the proportions of the elements. They are called the _Protoxide_, the _Black_ Oxide, and the _Peroxide_. We are here thrown back upon terms quite unconnected with the system. Other defects in the nomenclature arose from errours in the theory; as for example the names of the muriatic, oxymuriatic, and hyperoxymuriatic acids; which, after the establishment of the new theory of chlorine, were changed to _hydrochloric_ acid, _chlorine_, and _chloric_ acid. Thus the chemical system of nomenclature, founded upon the oxygen theory, while it shows how much may be effected by a good and consistent scheme of terms, framed according to the real relations of objects, proves also that such a scheme can hardly be permanent in its original form, but will almost inevitably become imperfect and anomalous, in consequence of the accumulation of new facts, and the introduction of new generalizations. Still, we may venture to say that such a scheme does not, on this account, become worthless; for it not only answers its purpose in the stage of scientific progress to which it belongs:--so far as it is not erroneous, or merely conventional, but really systematic and significant of truth, its terms can be translated at once into the language of any higher generalization which is afterwards arrived at. If terms express {277} relations really ascertained to be true, they can never lose their value by any change of the received theory. They are like coins of pure metal, which, even when carried into a country which does not recognize the sovereign whose impress they bear, are still gladly received, and may, by the addition of an explanatory mark, continue part of the common currency of the country.