Preparation and Purification of Reagents

The necessity for unusual care in the preparation of reagents and the handling of all materials cannot be overemphasized if reproducible results are to be obtained. While products haAnng luminescent properties satisfactory for some practical uses can be obtained without recourse to the detailed procedures described here, such methods must be employed whenever reliable and reproducible materials are desired. For tliis reason, the preparation and purification of some of the reagents are first described along with seAmral special techniques that have been found to be both useful and desirable. 

All glass and silica equipment employed should be cleaned with boiling nitric acid and washed with distilled water. Final washing should be made with twice distilled water. 

The use of chromic acid cleaning solution must be avoided to prevent introduction of chromium. Flasks should be kept covered with inverted beakers to eliminate contamination from dust. 

After the first step in the purification operations, any water that is used must be twice distilled, the second distillation being carried out in all-glass stills. 

Where purified nitric acid is specified the purification is achieved by distilling reagent-grade nitric acid in a silica 

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