It appears, that the milk requires a large quantity of the water, to make a sensible coagulation in it: for, in the 22d experiment, one part of the milk being added to four parts of the mineral water, the coagulation was scarcely discernible: and in the 23d, when an equal or larger quantity of milk was added to the water, the coagulation was not at all observable. I have heard it confidently averred, that this mineral water did not at all curdle milk; which, I suppose, has been thro' a mistake in the experiment, in adding too large a proportion of milk to the water: for in this way the coagulation cannot be observed.
I imagined, that when the water was boiled with milk, the mixture would have become of a muddy yellow colour, by the separation of the ochre: but it did not even appear, that the ochre was at all separated from the mixture, as it is from the water when boiled by itself. On the contrary, not only the coagulum, but also the liquor, was of a pure white colour, and of a pleasant taste: and this makes me think it worth the inquiring into, whether or not the water does retain its medical qualities after it is prepared in this manner with milk? For, if it does, such a preparation might certainly be very serviceable in many cases.
These experiments, which we next relate, do not only ascertain the existence of alum in the water with greater certainty, but also, that there is a particular kind of earth conjoined with this salt.
Exp. 26. An English quart of the water being kept boiling for a quarter of an hour, it turned thick, muddy, and yellow, by the separation of its ochrous parts; and, being set to cool in a clean bowl, the next day all the ochre was subsided to the bottom, from which the water was carefully filtred: whereby it became almost as clear and limpid as before the elixation, retaining a sharp aluminous taste, but was deprived of the strong ferrugineous taste, which it had at first. This water was again boiled; by which means it was again turned a little yellow, by the separation of some more ochre. It was therefore again filtred, and rendered clear, and its aluminous taste was stronger than before. After this filtration, the water was evaporated in a sand-heat to about a sixteenth part of the original quantity, and then it tasted like a strong solution of alum joined with a small degree of a chalybeat taste. And this being totally evaporated in a glass, there adhered upon its sides a pure white salt; and a larger quantity of the same salt remained in the bottom of the glass, which was not so white, but more impure than the former, and of a brown colour.
27. This salt, thus procured from the water, being mixed with distilled vinegar and spirit of vitriol, there was not the least effervescence produced.
28. Some of the brown-coloured salt being put upon a red-hot iron, it did neither sparkle nor decrepitate; but was turned into a blackish cineritious substance, which in a short time became a white calx. And tho' some of the salt was put upon the iron finely powdered, yet it concreted, and run together in a cinder, whose cohesion was afterwards destroyed when calcined by a further degree of heat.
29. As I was accidentally deprived of the opportunity of obtaining crystals of this salt, which would have been the best means of knowing to what species it was to be referred; I dissolved the whole mass in a small quantity of spring-water, and, by filtrating this solution, I obtained a large proportion of fine earth of a brown colour.
30. This solution of the salt afforded a deep blue tincture with galls.
31. The same solution, being mixed with syrup of violets, became of a reddish colour.
32. Saccharum Saturni being added to the solution, precipitated a thick lactescent cloud.