Litmus "Lecanora tartarea" (Norway, Sweden), "Variolaria dealbata", "Ochrolechia parella", "Parmotrema tinctorum", and "Parmelia". Currently, the main sources are "Roccella montagnei" (Mozambique) and "Dendrographa leucophoea" (California). The main use of litmus is to test whether a solution is acidic or basic. Wet litmus paper can also be used to test for water-soluble gases that affect acidity or alkalinity; the gas dissolves in the water and the resulting solution colors the litmus paper. For instance, ammonia gas, which is alkaline, turn the red litmus paper blue. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or
Olive oil acidity by the European Commission regulation No. 2568/91) is a manual titration procedure: a known volume of the oil to be tested is added to a mix of ether, methanol and phenolphthalein, known volumes of potassium hydroxide KOH 0.1M (the titrant) are added until there is a change in the color of the solution. The total volume of added titrant is then used to estimate the free acidity. The official technique for acidity measure in olive oil is accurate and reliable, but is essentially a laboratory method that must be carried out by trained personnel (mainly because of the toxic compounds