classifying substances of so very opposite natures, under the same generic name, would have been quite contrary to our principles of nomenclature, especially as, by retaining the above term for this state of metallic substances, we must have conveyed very false ideas of its nature. We have, therefore, laid aside the expression _metallic calx_ altogether, and have substituted in its place the term _oxyd_, from the Greek word [Greek: oxys]. By this may be seen, that the language we have adopted is both copious and expressive. The first or lowest degree of oxygenation in bodies, converts them into _oxyds_; a second degree of additional oxygenation constitutes the class of acids, of which the specific names, drawn from their particular bases, terminate in _ous_, as the _nitrous_ and _sulphurous_ acids; the third degree of oxygenation changes these into the species of acids distinguished by the termination in ic, as the _nitric_ and _sulphuric_ acids; and, lastly, we can express a fourth, or highest degree of oxygenation, by adding the word _oxygenated_ to the name of the acid, as has been already done with the _oxygenated muriatic_ acid. We have not confined the term _oxyd_ to expressing the combinations of metals with oxygen, but have extended it to signify that first degree of oxygenation in all bodies, which, without converting them into acids, causes them to approach to the nature of salts. Thus, we give the name of _oxyd of sulphur_ to that soft substance into which sulphur is converted by incipient combustion; and we call the yellow matter left by phosphorus, after combustion, by the name of _oxyd of phosphorus_. In the same manner, nitrous gas, which is azote in its first degree of oxygenation, is the _oxyd of azote_. We have likewise oxyds in great numbers from the vegetable and animal kingdoms; and I shall show, in the sequel, that this new language throws great light upon all the operations of art and nature. We have already observed, that almost all the metallic oxyds have peculiar and permanent colours. These vary not only in the different species of metals, but even according to the various degrees of oxygenation in the same metal. Hence we are under the necessity of adding two epithets to each oxyd, one of which indicates the metal _oxydated_[15], while the other indicates the peculiar colour of the oxyd. Thus, we have the black oxyd of iron, the red oxyd of iron, and the yellow oxyd of iron; which expressions respectively answer to the old unmeaning terms of martial ethiops, colcothar, and rust of iron, or ochre. We have likewise the gray, yellow, and red oxyds of lead, which answer to the equally false or insignificant terms, ashes of lead, massicot, and minium.