This cremor, which is separated from the water, is the same with that, which appears on the surface of a solution of vitriolum Martis, when exposed for some time to the air; and an infusion of iron in common water also emits a cremor of the same kind. I remember, as I was once carefully observing a large glass full of chalybeat water, which contained much of this cremor; soon after it was exposed to the air, I observed a tenuious blueish vapour rising in the parts of the water next the surface, which very much diminished its transparency; and by degrees this vapour was emitted by the lowest parts of the water: but as the cremor increased on its surface, the water became gradually deprived of the blueish tincture, which it received from this halituous body; which was apparently nothing else but the parts of the cremor separating from the water, and ascending upwards. From whence we may conclude, that this cremor consists of the very finest part of iron attenuated to the highest degree. It has been the opinion of most naturalists, that these kind of mineral waters do abound in sulphureous parts. This they have conjectured from the foetor, that often attends them. But in what quantity or form these parts exist in the fluid, or by what means they can be rendered conspicuous, has not as yet been sufficiently determined. Yet, I think, we may suspect some of the parts of this cremor to be sulphureous. They are volatile, and, being heated, do fly off from the pure metalline parts, which being more fixed, are thereby left destitute of those vivid colours, which they enjoyed from the sulphureous parts. These are evident marks of sulphur, and are altogether analogous to some other appearances of that mineral. Another observation tending to support this is the want of those vivid colours in the cremor, which appears on an infusion of iron; the reason of which seems to be the loss of the sulphureous parts of the chalybeat minerals by avolation, during the operations of the fire, which they undergo in refining. It appears from the fifteenth experiment, that the water of these two springs contains a very different proportion of this cremor: and from the last, that it is precipitated along with the ochrous parts, which happens upon the affusion of these alkaline liquors. The next trials were in quest of alum. _Exp._ 17. A quantity of the water being kept for some time in a boiling heat, and after it was cool being filtred quite clear from its ochrous matter, it still retained a subacid and aluminous taste in a very strong degree. 18. To an ounce of common spring-water there was added two gutts of fresh sweet milk. This mixture being shaken, the milk mixed intimately with the water, without any kind of coagulation. 19. The same experiment being made with the mineral water, the milk, upon its affusion, was so curdled, or separated into clouds, that the greatest shaking could not mix or incorporate it with the water.