Dip into the above solution a piece of paper: if its colour be changed
to brown, a drop or two more acid must be cautiously applied: if,
on the contrary, it reddens litmus paper, a small globule or two of
potassium will be required; the object being to obtain a neutral
solution: if it then be carefully evaporated to about half its bulk,
and set aside, beautiful crystals will begin to form, which will be
those of the nitrate of potash, commonly called nitre, or saltpetre.