《梦溪笔谈·杂志二》
信州铅山县有处泉水叫苦泉，水流成为山间溪水，舀取其水煎熬就能熬成胆矾，再熬胆矾就能熬成铜。
信州铅山县有苦泉，流以为涧。挹其水熬之，则成胆矾。
In Lingshan County, Xinzhou, there is a spring called Bitter Spring, whose flowing water forms a mountain stream. The water can be scooped up and boiled to make copperas, and the copperas can be further boiled to make copper.