Abstract
THE STABILITY OF DILUTE STANDARD SOLUTIONS OF SB (4 MICROGRAMS/ML), AS (20 MICROGRAMS/ML), FE (50 MICROGRAMS/ML), AND RE (5 MICROGRAMS/ML) USED IN COLORIMETRY WAS STUDIED BY COLORIMETRIC PROCEDURES OVER A PERIOD OF TWO MONTHS. THE SOLUTIONS WERE STORED IN SODA-GLASS, BOROSILICATE GLASS, AND RIGID POLYETHYLENE CONTAINERS. THE DILUTE STANDARD ANTIMONY SOLUTIONS, PREPARED EITHER BY DISSOLVING ANTIMONY POTASSIUM TARTRATE IN WATER, OR BY DISSOLVING ELEMENTAL ANTIMONY IN SULPHURIC ACID AND DILUTING THE SOLUTION WITH WATER, WERE FOUND TO BE STABLE (I.E., TO DETERIORATE BY LESS THAN 3 PERCENT) OVER A PERIOD OF 50 DAYS. ANTIMONY SOLUTIONS CONTAINING HYDROCHLORIC ACID DETERIORATED RAPIDLY, HOWEVER. THE DILUTE STANDARD ARSENIC SOLUTIONS PREPARED EITHER BY DISSOLVING ARSENIC (III) OXIDE IN SODIUM HYDROXIDE SOLUTION AND THEN NEUTRALIZING THE SOLUTION WITH HYDROCHLORIC ACID, OR BY DISSOLVING DISODIUM HYDROGEN ARSENATE HEPTAHYDRATE IN WATER, WERE FOUND TO BE STABLE. ARSENIC (III) IN THE FORMER STANDARD SOLUTION WAS OXIDIZED SLOWLY BY DISSOLVED OXYGEN, BUT THE TOTAL ARSENIC PRESENT IN THE SOLUTION REMAINED UNCHANGED AND COULD BE DETERMINED BY THE MOLYBDENUM-BLUE METHOD. AN IRON (III) STANDARD SOLUTION, 0.06 M IN HYDROCHLORIC ACID AND PREPARED FROM AMMONIUM IRON (III) SULPHATE, WAS STABLE FOR AT LEAST 2 MONTHS, AS WAS A STANDARD POTASSIUM PERRHENATE SOLUTION IN A BUFFER SOLUTION OF PH 6. LIGHT IN THE LABORATORY AND THE MATERIAL OF THE CONTAINERS DID NOT ADVERSELY AFFECT THE SOLUTIONS REPORTED TO BE STABLE. (LITTLE-BATTELLE)