Chemical tests in mushroom identification are methods that aid in determining the variety of some fungi. The most useful tests are Melzer's reagent and potassium hydroxide.
Ammonia
Household ammonia can be used. A couple of drops are placed on the flesh. For example, Boletus spadiceus gives a fleeting blue to blue-green reaction.
Iron salts
Iron salts are used commonly in Russula and Bolete identification. It is best to dissolve the salts in water and then apply to the flesh, but it is sometimes possible to apply the dry salts directly to see a color change. For example, the white flesh of Boletus chrysenteronstains lemon-yellow or olive. Three results are expected with the iron salts tests: no change indicates a negative reaction; a color change to olive, green or blackish green; or a color change to reddish-pink.
Meixner test for amatoxins
The Meixner test uses concentrated hydrochloric acid and newspaper to test for the deadly amatoxins found in some species of Amanita, Lepiota, and Galerina. The test yields false positives for some compounds, such as psilocin.
Spores that stain bluish-gray to bluish-black are amyloid
Spores that stain brown to reddish-brown are dextrinoid
This test is normally performed on white spored mushrooms. If the spores are not light colored, a change will not be readily apparent. It is easiest to see the color change under a microscope, but it is possible to see it with the naked eye with a good spore print.
A 2–3% aqueous solution of phenol gives a color change in some species when applied to the cap or stem.
Potassium hydroxide
A 3–10% solution of potassium hydroxide gives a color change in some species of mushrooms:
In Agaricus, some species such as A. xanthodermus turn yellow with KOH, many have no reaction, and A. subrutilescens turns green.
Distinctive change occurs for some species of Cortinarius and Boletes
Schaeffer reaction
Developed by Julius Schäffer to help with the identification of Agaricus species. A positive reaction of Schaeffer's test, which uses the reaction of aniline and nitric acid on the surface of the mushroom, is indicated by an orange to red color; it is characteristic of species in the sectionFlavescentes. The compounds responsible for the reaction were named schaefferal A and B to honor Schäffer. Two intersecting lines are drawn on the surface of the cap, the first with aniline or aniline water, the second with an aqueous solution of 65% nitric acid. The test is considered positive when a bright orange color forms where the lines cross. Agaricus placomyces and Agaricus xanthodermusproducefalse negative reactions. Sometimes referred to as "Schaeffer's reaction", "Schaeffer's cross reaction" or "Schaeffer's test".
