The Third Part of the Prosperity of Germany

the text references Lazarus Ercker, a 16th-century metallurgist and author of a famous treatise on ores and assaying Lazarus Ercker has written at length. But the recognition of the stones and their preparation, so that they may communicate their nitre to water, is the primary thing, and without it nothing at all can be accomplished in this operation.

First of all, it is necessary that the philochymicus lover of chemistry/alchemist know how to find various stones that exhibit saltpeter, namely all those from which lime is commonly made by the force of fire for the construction of buildings. For in such stones, a great deal of saltpeter lies hidden, which by the help of common water can in no way or by any method be drawn out from them. But when the same are burned by violent fire, they exhibit a hot salt, to be extracted by the benefit of common water, which salt is indeed not yet saltpeter, but can most easily be changed into saltpeter through the air, just as before the stone was burned, it was saltpeter and had first attained another nature through burning.

The truth of this matter, that natural saltpeter resides in all stones that can be burned into lime, can be proved in the following way.

Take half an ounce or one ounce of such stones from which lime can be prepared. Pulverize them very finely, and pour onto them the same amount of the best Aqua fortis nitric acid. Let the glass in which this matter is contained be placed in a warm place over ashes or sand so that the stone may be dissolved by the Aqua fortis. After it has stood thus for about a quarter of an hour, remove the glass from the sand or ashes, even if the stone has not yet been entirely dissolved, and pour