From these experiments it is evident, that there is a considerable difference betwixt the waters of the two springs. The upper one contains a much larger quantity of ochrous earth, and metalline cremor, than the under one; which is the reason, why it yields a deeper colour with galls, as may be observed in the first experiment. I suspected, on the other hand, that the under water contained a greater proportion of alum, than the water of the upper spring; but this I cannot affirm, as I find I had neglected to make the experiment, which would have determined whether it be so or not. Tho’ the mineral contents of these two waters be similar, yet, if they be thus mixed in them in different proportions, this must certainly create a difference between them, which deserves to be attended to, as it may be sufficient to disallow of their being used promiscuously, since their medicinal effects may be thereby different. But now, to sum up the evidence, which these experiments, taken all together, do afford, concerning the mineral ingredients of this Spaw; I think they determine, with some degree of certainty, that it contains two different principles of iron, both of which are fixed. The one, which is the ochrous earth, is a true _minera ferri_, and, altho’ it be a crude mineral, exists in the water in a very fine and subtile form; the other, which is the cremor or pellicle, whose parts are also extremely attenuated in the water, appears to be iron, not in its mineral, but in its metalline form, and, when thrown up upon the surface of the water, shews itself like an extreme thin _lamina_ of that metal. There seems also to be some small proportion of sulphur joined with the metalline cremor. The other mineral ingredient, which enters into the composition of this Spaw, is a considerable proportion of an aluminous salt, which is conjoined with a small quantity of a light brown-coloured earth (probably a part of the matrix whence the salt is formed), and still more intimately connected with some of the chalybeat parts of the water, which are not separable from it either by elixation or evaporation. Whether these be saline or terrestrial, I cannot determine. Having thus endeavoured to discover, by some plain and simple experiments, the mineral principles, with which this medicinal water is impregnated; I shall now only add some observations, with respect to the origin of steel waters, and particularly of this Spaw, whose origin, I think, is thereby discovered and ascertained in a very obvious manner.