Litmuspaper

Used for general testing for acid or alkaline reaction. Testing during neutralization or whether transition from acid to alkaline or vice versa has already occurred. Litmus paper is the best known indicator paper. Color change from violet to red or blue, and in the direction of acid red, in the direction of alkaline blue. Litmus is a natural product and chemically not a precisely definable uniform substance. It is obtained from lichens. It is probably the oldest indicator dye.