FED-STD-791D
The specific gravity of this solution shall be between 1.027 and 1.041 when measured at
35 1C (95 2F). Maintain the pH of the solution between 6.5 and 7.2 by the
addition of either hydrochloric acid or sodium hydroxide as necessary. Determine the
pH of the salt solution electrometrically or colorimetrically using bromothymol blue as an
indicator.
6.1.2 Twenty percent solution. Dissolve 20 2 parts by weight of sodium
chloride in 80 2 parts by weight distilled water. Filter the solution if there is any
suspended matter. The specific gravity of this solution shall be between 1.1267 and
1.157 when measured at 35 1C (95 2F). Maintain the pH of the solution
between 6.5 and 7.2 by the addition of either hydrochloric acid or sodium hydroxide as
necessary. Determine the pH of the salt solution electrometrically or colorimetrically
using bromothymol blue as an indicator.
6.2 Preparation of panels for testing.
6.2.1 Cleaning of panels. Handle all panels as little as possible, particularly on
the significant surfaces. Clean uncoated metal panels with warm 38 to 54C (100 to
130F) 1,1,1-trichloroethane and cleaning tissue. Clean all significant surfaces until they
are free from water-break. If a panel has an organic coating, do not clean it with an
organic solvent. Dry all panels thoroughly. Coat the edges of panels which may come in
contact with supports with wax or with some material which is impervious to moisture.
6.2.2 Application of coatings to panels. Fluid, semi-solid, or solid coatings (see
1.1) shall be applied to test panels in accordance with product specification.
6.3 Location of panels in the exposure chamber. Test panels shall be supported
in such a manner that the significant surfaces are approximately 15 from the vertical
position and are parallel to the principal direction of horizontal flow of fog through the
chamber. Whenever practicable, the panels shall be supported from the bottom or from
the side. When panels are suspended from the top, suspension shall be accomplished
with glass hooks or waxed string. The use of metal hooks is not permitted. The panels
shall be positioned so that they do not shield each other from the freely settling fog, and
so that corrosion products and condensate from one panel do not fall upon another.
6.4 Operating conditions.
6.4.1 Temperature. The test shall be conducted with a temperature in the
exposure zone maintained at 35 +1, -1.5 C (95 +2, -3 F). Satisfactory methods for
controlling the temperature accurately are by housing the apparatus in a properly
controlled constant temperature room, by thoroughly insulating the apparatus and
preheating the air to the proper temperature prior to atomization, and by jacketing the
apparatus and controlling the temperature of the water or of the air used. The use of
immersion heaters for the purpose of maintaining the temperature within the chamber is
prohibited.
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