Notice the Bacstrom papers. Guess what?
Based on his wide readings, he was convinced the Stone was made with 3 basic substances (which in reality two of them were the product of reactions involving 5 separate raw substances, while another one was just a metal and only required purification.)
This statement shows a lack of understanding and is also completely unfounded.
Have you read Sigismond Bacstrom's works? Do you recall the part where he said "This is the subject of the Stone or Medicine of the Philosophers. The more you take this in its simple, universal, unspecified or unmarried state, the easier, simpler and greater is your work"? What about the part where Bacstrom said "The subject contains fire, air, water and earth, and requires no addition of any foreign matter, except when introduced into the metallic department"?
I blame the nefarious influence of many chymical writers (specially Starkey/Philalethes)