UU-P-236a
been explainedsatisfactorily, the rate of flow of liquids through filter paper, and other porous materials, becomes progressively slower with continued flow. It has been found, however, that the change in rate can be almost eliminated for filter paper by preD filtration of the water used in making the test.
4.3.5Retention of precipitates.-Retention
of precipitates shall be determined by examD
ining the filtrate, which shall be caught in an
Erlenmeyer flask, for any precipitate that may pass through the filter paper. Swirl the filtrate to bring any precipitate to the center and view from above against a black backD ground. The precipitates shall be prepared as follows:
4.3.5.1 Ferric hydroxide, cold. - Add a slight excess of dilute ammonium hydroxide to cold ferric chloride solution and shake. Make fresh each time and use immediately.
4.3.5.2Lead sulfate, cold.-Prepare a soluD tion of lead acetate by dissolving 10 grams of the anhydrous salt or 11.5 grams of the trihydrate in water and dilute to 100 milliD liters in a graduated cylinder. Filter through a class 7 filter paper and add 40 milliliters of
6N sulfuric acid and 80 milliliters of alcohol. Filter after standing for 4 hours. Wash the precipitate with dilute sulfuric acid (5 milliD
liters concentrated acid in 100 milliliters of water), then with alcohol.
4.3:5.3Barium sulfate, hot.-Dissolve 0.55 gram of K2S04in 275 milliliters of water and add 1.0 milliliter of concentrated HCI. This solution contains the equivalent of about 0.74 gram of BaS04.Heat to boiling,and while at the boiling temperature, add slowlyand with continuous stirring 25 milliliters of a 5-perD cent solution of BaCh,2H20. It is very imD portant to have the specified concentration of acid and to keep the solutionat the boiling temperature during the precipitation. Let stand without agitation in a boiling water bath for 2 hours ± 15 minutes. Stir the preD cipitate until it is evenly suspended in the
liquid, and filter approximately 50 milliliters of the mixture through each circle of paper.
4.3.6 Diameter of circles.-The diameter of not less than 10 circles shall be measured and the average of the measurements reD ported to the nearest 0.1 centimeter.
5. PREPARATION FOR DELIVERY
5.1Packaging.-Circles of filter paper shall be packagedin cartons, 100per carton. Other forms of filter paper shall be packaged acD cording to commercialpractice.
5.2 Packing.- Packages of filter paper shall be overpacked in an exterior container constructed in accordance with the requireD ments of Federal Specification NN-B-601, NN-B-621, or NN-B-631. Unless otherwise specified,gross weight of the container shall not exceedapproximately 100pounds. Unless otherwise specified,only one type, class, and size of filter paper shall be packed in each shipping container.
5.3 Marking.
5.3.1 Cartons. - Each package shall be marked with the stock number, name of the commodity,the type, class, unit, and quanD tity contained therein, and the name of the contractor and manufacturer. In addition, each carton containing class 5, class 6, class
7, and class 8 filter papers shall be marked
with the weight of ash per circle.
5.3.2 Shipping containers.-Shipping conD tainers shall be marked on one side with the name of the commodity,the type, class, size, and quantity contained therein, as defined by the contract or order under which the shipment is made,the name of the contractor, and the number of the contract or order.
6. NOTES
6.1 Ordering data.-Purchasers should exD ercise any desired options offeredherein and should specify the type, class, and size of filter paper required. (See 1.2,1.3, and 7.2.5.)
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