In an experiment, addition of 5 ml of 1M NaCl  to 100 ml of arsenious sulphide sol just causes the complete coagulation. The flocculating value of NaCl is:

Flocculating value =millimoles of the electrolyte per litre of sol for complete coagulation No of millimoles of NaCl present in 5ml of 1M NaCl = 5×1 = 5100ml of arsenious sulphide sol require 5 milli moles of NaCl for complete coagulation 1000ml of arsenious sulphide sol require 50 millimoles of NaCl for complete coagulation.