O-S-801F
4.3.5 Specific gravity. Determine the specific gravity of the specimen using a suitable precision hydrometer standardized at 15.6 oC (60 oF), referred to water at 15.6 oC (60 oF). Make temperature corrections, when necessary, for deviations from the standard temperature
as shown in table IV. When the temperature of the acid is above the standard temperature, add the correction to the observed specific gravity; when the temperature of the acid is below the standard temperature, subtract the correction from the observed specific gravity factor.
TABLE IV. Correction for temperature deviation.
Class of sulfuric acid |
Correction per degree of temperature deviation |
|
oC |
oF |
|
1 2 3 4 |
0.00097 0.00074 0.00070 0.00065 |
0.00054 0.00041 0.00039 0.00036 |
4.3.6 Organic matter. Heat 50 ml of the specimen in a clean beaker until the sulfuric acid begins to fume strongly. To pass test, there shall be no perceptible charring; a slight yellow color that appears when a specimen is hot but disappears on cooling should be disregarded.
4.3.7 Platinum. As applicable, evaporate 10 ml of class 1, 24 ml of class 2, 36 ml of class 3, or
52 ml of class 4 specimen to dryness in a small porcelain evaporation dish set on a sand bath, but do not heat the residue unnecessarily. Cool and add 2 ml of aqua regia (4 volumes of hydrochloric acid and 1 volume of nitric acid). Cover the dish with a watchglass and digest on a steam bath for 10 minutes. Remove the watchglass and evaporate the solution to five or six drops. (If the solution accidentally evaporates completely, repeat the digestion with aqua regia and reevaporate to five or six drops.) Absorb the solution (five or six drops) in a piece of thin asbestos paper preferably not over 0.75 mm thick and about 0.5 cm wide and 3 cm long. (Hold the paper in a pair of crucible tongs and dip half of the paper into the solution. Dry gently over a flame. Repeat the dipping and drying operation until all of the solution has been absorbed into the asbestos paper.) Dry the paper and ignite to redness in a moderate Bunsen flame (3 to 4 inches high with good air mixture). With the asbestos paper held vertically in the Bunsen flame, momentarily shut off the flow of gas and then turn it on again so that the stream of unignited gas plays on the hot asbestos paper. Glowing of the paper indicates the presence of platinum or one of the platinum metals other than osmium or ruthenium. (Note: The glow should persist; however, if it dies out, it may be brought back by reigniting the paper, although this cannot be repeated indefinitely.) The presence of platinum shall not be indicated.
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