Appendix Cresol

Using Appendix B, you would choose bromthymol blue (range 6.0 to 7.6, Lower color-yellow Upper color-blue) and m-Cresol purple (range 7.5 to 9.0, Lower color-yellow Upper color-violet) because bromthymol blue s high-end color (blue) ends where m-cresol purple s low-end color (yellow) begins. The pH would be between 7.5-8.5. 

Assay Determine as directed under Solidification Point, Appendix IIB, drying a sample over anhydrous sodium sulfate. Transfer 3 g of the dried oil, accurately weighed, into a test tube, and add 2.1 g of melted o-cresol. The o-cresol must be pure and dry and have a solidification point not below 30°. Insert the thermometer, stir, and warm the tube gently until the mixture is completely melted. Continue as directed in the method. Repeat the procedure until two successive readings agree within 0.10°. Compute the percentage of cineole from the table found under Percentage of Cineole, Appendix VI. Acid Value Determine as directed under Acid Value, Appendix VI. 

According to the previously cited reference (Hof nan, (1991), Appendix A), some dyelike materials show up as inhibitors of glutaminolysis. Thus, the agents listed as bromcresol (or bromocresol) green and bromcresol purple are dyes derived from sulfonephthalein, starting with the compound called mcto-cresol. Cresols in turn are related to phenol or carbolic acid, and to the coal-tar mixture called creosote. Phenolic-type compounds are also known to occur in chaparral or creosote bush (genus Larrea), hence its alternate common name. 

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