the etchant is a newtonian liquid and the dynamic viscosity cannot be used measurements with a capillary viscometer reveal the viscosity behavior of koh and k 2 h 2 sio 4 is different in the concentration region of interest the effect of k 2 h 2 sio 4 is more linear than that of koh mainly because of the narrower concentration range fig3 depicts the refractive index solid line and viscosity dashed line behavior of the etchant by looking at the angle between the curves it seems that there are regions where the two measurements can be used to solve the concentrations especially at low end of c koh unfortunately at a very important region of interest around c koh 0 32 and c k 2 h 2 sio 4 0 02 the measurement is impossible as the curves are parallel with chemical and electrochemical measurements there is a direct interaction between the measurement system and the medium under measurement there are numerous laboratory measurements which involve a chain of reactions to indicate or measure some property of the liquid in general these methods are not directly applicable to automated process measurements thus the discussion below is limited to electrochemical reactions and simple indicator reactions there are several electrochemical measurement methods the simplest being conductivity conductivity measurement is not a very useful measurement in the case of highly conductive solutions due to the high concentration of koh the solution has high electric conductance and the.