By total soluble salts in the soil we mean the various chemical materials which are in the soil and dis solve rather easily in water. In our laboratory we mix one part of dry soil with 2 parts distilled water and stir frequently for 30 minutes. Chemicals in the soil dissolve in the water. Then the solution is tested with an electrical gadget called a "Solu - bridge." This instrument tells how easily an electrical current is carried through the soil solution; the more soluble salts in the soil solution, the more easily the current is conducted, and the greater the conductivity reading.
Source: • New York State Flower Growers Incorporated, Bulletin #137