Litmus PH Tester Strips
Booklet size: 4.5 CM x 6.5 CM
 
How to use these pH strips:
To perform the test, place a drop of liquid sample onto the strip or dip a piece of litmus paper in a small specimen of the sample. Ideally, don't dip litmus paper in an entire container of a chemical—the dye could contaminate a potentially valuable sample. 
 
Because the strip contacts an acidic or alkaline substance, the strip discolors. The more acidic the fabric, the redder the strip becomes, and the more alkaline the fabric, the bluer the strip becomes. Using the indicator scale with the different colors on the box, you can determine how acidic or alkaline the liquid you measured is.
 
Disclaimer:
This litmus test is quick and simple, but it has a few limitations. The strips read approximate pH levels but they don't yield exact numerical pH values. They roughly indicate whether a sample is an acid or a base.