Mineral spirits (or petroleum spirits), a class of hydrocarbon solvents, vary greatly in composition, depending on the source of the crude oils and the refining processes used in their production. Consequently, it is not a simple problem to prepare testing procedures and specifications that will give all the desired information concerning the performance characteristics of hydrocarbon solvents when used in organic protective coatings. Subcommittee V, recognizing the need for test procedures to indicate performance characteristics, has standardized several procedures designed to indicate the elusive property of solvency. Solvency of hydrocarbon solvents is a rather indefinite characteristic and cannot be completely evaluated by any single test. It is a relative term used to indicate the effect of dissolving or dispersing a resin, oil, or combination of resin and oil in a hydrocarbon solvent. The nature of the material being dispersed or dissolved is as important as the composition of the solvent. Solvency may be expressed in different values, depending on the test used, such as Kauri-Butanol Value, Aniline or Mixed Aniline Point, Heptane Number, Nitrocellulose Diluting Power, and Viscosity Reducing Power. For many years, the Kauri-Butanol Value (or Number) was the generally accepted test for solvency determination, although many realized its inadequacy. Since this test was in common use by both producer and consumer, Subcommittee V undertook its standardization. Earlier work by the Philadelphia Paint and Varnish Production Club on Kauri-Butanol procedure served as a basis for a cooperative test program by Subcommittee V resulting in a tentative method of test for Kauri-Butanol Value of hydrocarbon solvents (D 1133).