Abstract: Long chain polymer flow promoting additives including guar gum, polyethylene oxide and polyacrylamide used to maintain Newtonian flow characteristics in an extended velocity range are mixed into a neutral density liquid having a significant variation of electrical conductivity with the dilution of the neutral density liquid, to provide a stable additive mixture. The concentration of the neutral density carrier liquid when diluted as a working liquid in use within a machine or system may be readily determined by measuring the electrical conductivity of the working liquid, thus permitting the working liquid content of flow promoting additive to be readily determined and controlled.