After having been dried as far as possible, the crystals are then put in a clean porcelain vessel and ground to powder with a pestle. While grinding, a quantity of as much as possible arsenicfree blossoms of sulfur – to one teaspoonful of the salt a quarter of that – is added and well mixed into the other powder. This mixture is then the sulfate to be used as described above for the required purpose. – The Healing Power of Sunlight, Chapter 5, Paragraph 15