This is an example of the PH scale. It has an example of a substance that has the PH indicated. The PH scale can be represented horizontally or vertically. To know the PH of a substance, you need an indicator. Some examples of indicators are: Universal Indicator, Blue Litmus Paper and Red Litmus Paper. The Universal Indicator tells you exactly the PH of every substance. The Blue Litmus Paper works like this: if it goes red, it´s an acid and if it stays blue, it´s an alkali. The Red Litmus Paper works like this: If it goes blue, it´s an alkali and if it stays red, it´s an acid.