Colorimeiric Estimations The samples were renAl iii a photoelectric colorinseter with a red-orange filter (a cons- bination of Ilford 803 amsd 205). When this filter is used, solutions of hen’soglobin absorb very little light imu comparisoms with that absorbed by solutions of Evans blue. Since, in additions, the plasma was (hiluted hetweets 250 amid 500 timnes, errors caused by slight hemolysis were mieghigible