Claims that medicines swallowed by mouth could dissolve stones in the bladder seemed a priori unlikely. Yet there was considerable authority that this took place; many persons had reported that this was a _fact_. Boyle kept an open mind. He might be highly skeptical in regard to the claims for any particular medication, but he did not deny the principle involved. The possibility that some fluid, when swallowed, could have a particular specific action on stones in the bladder, without affecting the rest of the body, he considered quite plausible through the analogy that quicksilver has an affinity with gold but has no effect upon iron. Furthermore, a substance than can corrode a solid body may nevertheless be unable to "fret" a different body which is considerably softer and thinner, if the "texture" does not admit the small particles.[55] Reasoning by analogy served to explain the logical plausibility. In other words, he was very open-minded. He refused to dismiss all such claims, and provided analogy as a reason for keeping his mind open; yet he refused to accept particular claims of medicine that dissolved stones, because the evidence was not convincing. We could scarcely ask for more. An important seventeenth-century medical document was the report of Sir Kenelm Digby, regarding the so-called "weapon salve." The essay describing this famous powder was written in 1657, and I have discussed it at some length elsewhere.[56] Here again Boyle keeps an open mind, saying, "and if there be any truth in what hath been affirmed to me by several eye-witnesses, as well physicians as others, concerning the _weapon-salve_, and _powder of sympathy_, we may well conclude, that nature may perform divers cures, for which the help of chirurgery is wont to be implored, with much less pain to the patient, than the chirurgeon is wont to put him to."[57] One great advantage of chemistry, thought Boyle, lay in the help it provided in investigating the _materia medica_. Chemistry, he thought, could help to purify many of the inorganic medicines and make them safer, without impairing their medicinal properties. Furthermore, chemistry could help investigate various medications customarily employed in medicine, where "there hath not yet been sufficient proof given of their having any medical virtues at all."[58] Boyle believed that by proper chemical analysis he could isolate active components, or, contrariwise, by failing to extract any valuable component, he could eliminate that medicine from use. While a major interest, perhaps, was a desire to provide inexpensive medicines, he was well aware that much of what went into prescriptions probably had no value. Furthermore, he felt that his chemical analysis could indicate whether value and merit were present or not.