FED-STD-228A
3.1.1.9 A 500-ml gas collecting burette is connected through a two-way stopcock to the sampling bottle.
A 500-ml aspirator bottle is connected to the gas burette by means of rubber tubing.
3.1.2 Starch indicator solution.
3.1.3 Standard iodine solution, 100 mg. per liter.
3.1.4 Standard sodium, thiosulfate solution.
3.1.5 Potassium iodide, 1 percent solution.
3.1.6 Acetic acid, 10 percent solution.
4. PROCEDURE
4.1 Preparation and standardization of solutions. The solutions shall be prepared and standardized as
follows:
4.1.1 Starch indicator solution. A fresh solution may be prepared for use each day by dissolving 1 gram
of soluble starch in 100 ml. of boiling distilled water. A solution that may be used for several days shall be
prepared by mixing 1 gram of soluble starch with 40 ml. of cold distilled water, boiling until solution is
complete, diluting to about 200 ml. with cold water and adding 2 grams of zinc chloride. The solution
shall be set aside for several hours and then decanted.
4.1.2 Iodine solution. A weighing bottle containing 2 grams of potassium iodine and 10 grams of distilled
water shall be weighed and then about 0.1 gram of reagent grade iodine crystals added to the solution on
the balance. The solution shall be accurately weighed to determine the amount of iodine added. The
solution shall then be accurately transferred to a volumetric flask and the volume made to 1 liter with
distilled water. The solution should be stored in a dark bottle in a cool, dark place.
4.1.3 Sodium thiosulfate solution. A sodium thiosulfate solution of approximately the same strength as
the iodine solution shall be prepared by dissolving 0.24 gram of reagent-grade sodium thiosulfate
(Na2S2O35H20) in distilled water and diluting to 1 liter. The solution shall be standardized against the
iodine solution. Since the solution gradually loses its strength, the strength of this solution shall be
checked against the iodine solution at frequent intervals. The strength of the thiosulfate solution shall be
calculated as follows:
E= F x C
S
where:
E=the iodine equivalent of sodium thiosulfate expressed as mg. of iodine per ml. of Na2S2O3.
F=the number of ml. of the iodine solution.
C=the concentration of the iodine in mg. per ml.
S=the number of ml. of sodium thiosulfate used to titrate the solution.
129
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business