Kauri-butanol value
The kauri-butanol value is an international, standardized measure of solvent power for a hydrocarbon solvent, and is governed by an ASTM standardized test, ASTM D1133. The result of this test is a scaleless index, usually referred to as the "Kb value". A higher Kb value means the solvent is more aggressive or active in the ability to dissolve certain materials. Mild solvents have low scores in the tens and twenties; powerful solvents like chlorinated solvents and naphthenic aromatic solvents have ratings that are in the low hundreds. For example the KB values for halogenated solvents are; 129 for 1-Bromopropane, 136 for dichloromethane, 90 for tetrachloroethylene and 64 for parachlorobenzotrifluoride. KB values for non-halogenated solvents vary more, aliphatic hydrocarbon solvents have KB values in the 30s meanwhile toluene has a KB value of 105.
In terms of the test itself, the kauri-butanol value of a chemical shows the maximum amount of the hydrocarbon that can be added to a solution of kauri resin in butanol without causing cloudiness. Since kauri resin is readily soluble in butyl alcohol but not in most hydrocarbon solvents, the resin solution will tolerate only a certain amount of dilution. "Stronger" solvents such as benzene can be added in a greater amount than "weaker" solvents like mineral spirits.