FED-STD-228A
4.1.1 The 0.1N potassium permanganate solution shall be prepared by dissolving 3.16 grams of reagent
grade in distilled water and making the volume to 1 liter. The solution shall be set aside for 1 week in a
dark place then filtered through a 1/8 inch glass fiber cloth and stored in a glass stoppered bottle
protected from the light by a heavy coating of black paint.
4.1.2 The actinometer solution shall be prepared by dissolving 6.30 grams of reagent grade hydrated
oxalic acid (H2C2O42H2O) or 4.50 grams of anhydrous oxalic acid (H2C2O2) and 4.20 grams of reagent
grade uranyl sulphate (UO2SO43H2O) in distilled water and diluted to 1 liter. The solution shall be stored
in a glass stoppered bottle painted with a heavy coat of black paint to protect the solution from light. An
automatic dispensing burette, shown on figure 4131B when heavily coated with black paint to exclude
light is suitable for storing and dispensing the solutions.
4.2 Standardization of solutions. The evaluating solution (potassium permanganate) shall be
standardized against reagent grade sodium oxalate in the usual way, with such precautions that its
strength shall be known within an accuracy of at least ±1 percent. The strength of the potassium
permanganate shall be expressed in terms of milligrams of anhydrous oxalic acid per ml. of solution. The
actinometer solution shall be titrated against the standard potassium permanganate. An accurately
measured volume of 50 milliliters of the actinometer solution shall be transferred to a tall form 200 milliliter
beaker, 20 to 25 milliliters of distilled water added, and the solution acidified with 5 milliliters of 1 to 3
sulfuric acid. The beaker shall be covered with a porcelain dish and the solution heated to 95°C (203°F)
in a light-proof water bath, transferred to an open glass water bath and maintained at this temperature
while resting on a flat, white-glass base. The solution shall be clearly seen by light from the glass base
illuminated by a "daylight" lamp. The hot solution shall be titrated with the standard potassium
permanganate evaluating solution from a dispensing burette while stirring constantly until an orange color
is obtained which persists for at least 30 seconds while stirring. The titrating shall be conducted in such a
way that the volumes of solution used are precise to within ± 0.05 milliliter.
4.3 Calibration of radiation. The intensity of radiation of the light shall be measured in terms of the
milligrams of oxalic acid decomposed per square decimeter per minute, and the quantity of radiation in
any given period of time shall be measured in terms of the milligrams of oxalic acid decomposed per
square decimeter. An accurately measured volume of the actinometer solution shall be transferred to the
quartz cell from a dispensing burette. The cell shall be immediately placed in the holder to prevent
exposure of the solution to light. The cell holder shall be mounted on the cylindrical rotating framework in
the lighting unit in a similar position as that of a rubber specimen holder. The solution shall be exposed to
the light under normal operating conditions for a suitable period of time. The time of exposure of the
actinometer solution shall be sufficient to decompose not less than 10 percent nor more than 30 percent
of the oxalic acid in the cell. At the end of the exposure period, the actinometer solution shall be
transferred from the cell to a 200-ml beaker and then titrated with the potassium permanganate
evaluating solution as described in 4.2. The quantity of the evaluating solution required for the titration
shall be designed as V1. A volume of the actinometer solution equal to that used in the exposure cell
shall be titrated under the same conditions, omitting the exposure to light, and the quantity of
permanganate solution required for the titration recorded as V2. The quantity of oxalic acid in mg., Q,
decomposed by the radiation is given in the equation Q=a (V2-V1) where a is the number of mg. of oxalic
acid equivalent to 1 ml. of evaluating solution. The quantity or dosage of radiation is expressed as Q/A
and the intensity of radiation as Q/At where A is the area of the cell, in square decimeters, and t is the
time of exposure in minutes.
135
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business