(a) Prepare chromic acid cleaning solution by slowly
adding 800 ml of concentrated sulfuric acid to 500 ml of a saturated
solution of potassium dichromate and water. Prepare the solution in
a sink, using a pyrex, or equivalent glassware container. Chromic
acid is more effective as a cleaning agent when it is heated, but the
solution should not be boiled. The solution is ineffective when it
develops a greenish color and should be discarded.
Handle the soluton with extreme care to avoid in-
jury. A face shield and rubber gloves should be
(b) Store standard solutions so as to avoid atmos-
pheric CO2 contamination.
Never use high-temperature ovens to heat volatile
fluids. An explosion may occur and injure person-
(c) Keep in mind the toxic and flammable properties
of alcohols when preparing alcoholic solutions. Heat the solution
using a hotplate, never an open flame, in a fume hood to increase the
rate of solution. Always use pyrex, or equivalent glassware when
preparing laboratory solutions. If a water-free solution is not
necessary, dissolve the solute in a small quantity of distilled water
before adding to the warm alcohol.
(d) Field conditions may require the substitution of
solvents. In this case, the rule of "like dissolves like" should be
followed. When in doubt as to the correct solvent to be substituted,
consult the appropriate reference. For example, toluene could
possibly be substituted for benzene in a solvent capacity, but
n-hexane would not serve the purpose.