<P> Litmus can be found in different species of lichens . The dyes are extracted from such species as Roccella tinctoria (South America), Roccella fuciformis (Angola and Madagascar), Roccella pygmaea (Algeria), Roccella phycopsis, Lecanora tartarea (Norway, Sweden), Variolaria dealbata, Ochrolechia parella, Parmotrema tinctorum, and Parmelia . Currently, the main sources are Roccella montagnei (Mozambique) and Dendrographa leucophoea (California). </P> <P> 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 . </P> <P> Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5--8.3 at 25 ° C (77 ° F). Neutral litmus paper is purple . Litmus can also be prepared as an aqueous solution that functions similarly . Under acidic conditions, the solution is red, and under basic conditions, the solution is blue . </P> <Table> <Tr> <Td_colspan="3"> Litmus (pH indicator) </Td> </Tr> <Tr> <Td> below pH 4.5 </Td> <Td> </Td> <Td> above pH 8.3 </Td> </Tr> <Tr> <Td> 4.5 </Td> <Td> ⇌ </Td> <Td> 8.3 </Td> </Tr> </Table>

Blue litmus paper turns red acid or base
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