Although Marggraf was more advanced in his arguments than these chemists, yet he was a child of his time. The luminescent and combustible, almost wax-like substance impressed him greatly. "My thoughts about the unexpected generation of light and fire out of water, fine earth, and phlogiston I reserve to describe at a later time." These thoughts went so far as to connect the new marvel with alchemical wonder tales. When Marggraf used the "essential salt of urine," also called _sal microcosmicum_, and admixed silver chloride ("horny silver") to it for the distillation of phosphorus, he expected "a partial conversion of silver by phlogiston and the added fine vitrifiable earth, but no trace of a more noble metal appeared."[8] Robert Boyle had already found that the burning of phosphorus produced an acid. He identified it by taste and by its influence on colored plant extracts serving as "indicators." Hankwitz[9] described methods for obtaining this acid, and Marggraf showed its chemical peculiarities. They did not necessarily establish phosphorus as a new element. To do that was not as important, at that time, as to conjecture on analogies with known substances. Underlying all its unique characteristics was the analogy of phosphorus with sulfur. Like sulfur, phosphorus can burn in two different ways, either slowly or more violently, and form two different acids. The analogy can, therefore, be extended to explain the results in both groups in the same way. In the process of burning, the combustible component is removed, and the acid originally combined with the combustible is set free. Whether the analogy should be pursued even further remained doubtful, although some suspicion lingered on for a while that phosphoric acid might actually be a modified sulfuric acid. Analogies and suspicions like these were needed to formulate new questions and stimulate new experiments. They are cited here for their important positive value in the historical development, and not for the purpose of showing how wrong these chemists were from our point of view, a point of view which they helped to create.