A litmus test uses a color scale that can tell you approximate acidity/alkalinity (on the 0 to 14 pH scale) - not just used to determine if you have a substance that is acid, basic, or neutral (unless that is the gradations of the test kit you use).
The sensitivity (and range) of the test-strip is a function of the choice of strips.
http://www.indigo.com/test-strips/ph-test-strips.htmlI would not be mixing those chemicals unless I had a hooded exhaust cabinet (as found in chemistry labs). If both are just phosphoric acid, they should mix without a worry of putting off any other gases, except for the dangerous
phosphoric acid fumes.
