There must needs be a very great quantity of iron in this water, when it yields as deep a colour with galls as a strong solution of sal Martis. I was indeed at first apprehensive, that this perhaps might not be owing so much to a large and uncommon proportion of chalybeat parts, as to the commixture of alum, which I judged to be in the water. But we see the contrary appears by these trials: for alum of itself affords no tincture with astringents, and, instead of rendering a solution of sal Martis with galls of a more intense colour, rather makes it lighter and more diluted. We see here, that the ferrugineous matter is intirely separated from the water by an infusion of galls. The like also happens by elixation; after which it is almost deprived of its tinging quality. Yet other chalybeat waters lose this quality by much less degree of heat. As there is an ochrous earth separated from all steel waters, when exposed to the air, which subsides to the bottom, and a metalline scum or cremor, which swim on their surface; we shall next consider the appearances, which they make in this water. _Exp._ 8. A solution of saccharum Saturni being dropt into common spring-water, left the upper parts of the water clear and colourless, but formed a lactescency towards the bottom. The same solution being added to the mineral water, soon turned it of a turbid yellow colour, which afterwards subsided, and formed a deep yellow cloud in the bottom of the glass; and below this yellow sediment there adhered to the bottom of the glass a whitish substance, which I took to be the metalline parts of the saccharum Saturni separated from the purer parts of the salt, which were still suspended in the water, and which made it of a muddy whitish colour. 9. Forty drops of oleum tartari per deliquium being added to an ounce of the water, made it of an uniform light yellow colour; but in an hour afterwards there were many small yellow terrene _nubeculæ_ formed in it. These the next day were more conspicuous, being thoroughly separated from the water, and precipitated to the bottom, leaving the water quite clear, as it was before the mixture. A small quantity of this limpid water being taken, it would afford no tincture with galls. It was then all poured off, except so much in the bottom of the glass as contained the above-mentioned clouds: to this there were some galls added, which in half an hour turned these clouds from a light yellow to a deep red colour, but did not change the colour of the water, in which they swam. 10. Immediately after the affusion of ol. tart. p.d. to the water, galls were added to the mixture, which tinged it of a deep and bright red colour. After standing for some time, there were red clouds precipitated to the bottom, and the water continued of a dusky opake red colour.