Solvents and Solutions

TM 5-6640-213-14

(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

used.

(b) Store standard solutions so as to avoid atmos-

Never use high-temperature ovens to heat volatile

fluids. An explosion may occur and injure person-

nel.

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.

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