《天工开物·上篇·作咸》
蓬草盐的来源不太可靠，蓬草有时好几年来一次，也有时一个月就来好几次，因此不能经常指望它。
凡蓬草盐不可常期，或数年一至，或一月数至。
The source of reed salt is not very reliable, sometimes once every few years, sometimes several times a month, so it cannot be relied on all the times.