The Third Part of the Prosperity of Germany

And although the use of Aqua fortis nitric acid is entirely useless for this kind of operation where a large quantity of that salt is to be extracted from stones, it is not for nothing that one knows the method of testing which stones abound most in saltpeter, so that if there is an intention to extract saltpeter from them, we may take those in which it is copiously present.

Besides these stones which commonly exhibit lime through calcination—which builders use—others are found from which no lime can be prepared by burning, and yet, without any prior calcination, a great deal of saltpeter can be extracted. He who takes delight in this work is bound, above all, to accurately recognize such stones, since no one easily persuades himself that saltpeter is contained in them. Nor do I believe that the method of extracting saltpeter from this kind of stone has ever been in use before this time. Whether there was no one who knew that the said salt was contained in them, or whether they judged it of no consideration, I do not know. This, however, is sufficiently certain to me: that the method of extracting saltpeter from them has never been observed and used in Germany, although a great quantity of it adheres to them, to be extracted by an easy method provided that we have knowledge of it.

Since, therefore, a sufficiently large quantity of such stones can be had in all places, and the saltpeter can be prepared from them more easily than from wood,