ph nearly 30 minutes later the cessation of caustic supply is detected by the sensor 40 as reflected by the sharp negative slope of curve b starting at time 6 7 simultaneously the orp curve c responds but with a negative slope of short deviation having a direct proportionality relation to the b curve response had the response pattern of curve c established up to time 6 7 hours been followed a sustained sharply positive slope locus should have occurred at time 7 0 hours the washer solution residual was measured at 0 0 points and 7 2 ph such is indicated by the inverse peak of curve b at that time in the meantime curve c provides very little response of any kind such apparent incapacitation seems to continue until time 8 3 hours when the curve responded with an inverse proportionality to an increase in caustic supply which originally entered the flow stream at time 8 0 hours at time 8 2 hours the washer 22 solution was measured to have 2 0 points residual and 9 2 ph another measurement at time 8 6 hours showed a residual of 30 0 points and 10 5 ph at time 8 9 hours the washer solution carried 22 0 points residual and 10 2 ph to be of any value and utility in controlling the causticizing segment of the.