from 160 of red lead; or 100 red lead yielded 1.2 oxygen, the same proportion as by sulphuric acid. These experiments point out 1.2 oxygen in 100 red lead as the excess which converts the yellow to the red oxide. Were any doubt to remain on the subject, the experiment with nitric acid and red oxide will remove it. If the red oxide contained a mean of oxygen between the yellow and the brown, when it is treated with nitric acid more than 50 per cent. of brown oxide would be obtained instead of 20, which is contrary to all experience. It must be observed that Berzelius informs us he extracted the yellow oxide, mechanically mixed (as he conceives) with the red oxide, by digestion with dilute acetic acid; but he does not inform us how much per cent. his minium was reduced by this operation. From what is stated above, it appears that about ½ of the whole is thus dissolved. The remaining half would then contain double the quantity of oxygen and brown oxide per cent. that the original did. Still these quantities are inadequate to explain the phenomena. Besides it cannot be admitted that a _red_ and a _yellow_ powder can be intimately mixed in equal quantities and the mixture not be distinguishable without difficulty from the _red_ one, and be altogether different from the _yellow_. We must then conclude that the minium of commerce (such as I have used) is a true chemical compound. Grounding our reasonings upon the preceding facts, there are but two suppositions that can be considered as plausible, respecting the constitution of the red oxide. It may be 1 atom of oxygen and 5 of yellow oxide, or 1 atom of oxygen and 6 of yellow oxide. The former would give 1.4 per cent. extra oxygen in 100 red oxide, and 21 brown oxide; the latter would give 1.2 per cent. extra oxygen and 18 brown oxide. I adopt the latter supposition; because it agrees with experiment in regard to oxygen, and gives the brown oxide a little _lower_ than experiment, as may be expected on two accounts; first, the residue of brown oxide contains the insoluble dross of the red oxide (which was very small however, as stated above); and, second, unless a considerable excess of nitric acid be used, or long digestion, a small portion of the red oxide escapes decomposition. Another and still more important consideration, as to the question whether 5 or 6 atoms, is the equal division of the red oxide by the operation of cold acetic acid; it reduces the 1 oxygen and 6 yellow oxide to 1 and 3 atoms; whereas if we adopt the other, we must conclude it reduces the 1 and 5 to 1 and 2½, a position that cannot well be reconciled to the atomic theory.