This Prussian blue may then be placed in evaporating dishes, and gently dried. To form the Prussian blue, so operated upon, into a solution, oxalic acid is added, and carefully mixed with it, after which cold water is added (cold distilled water is best) a little at a time, making it into a dense or dilute solution, according to the color required. The quantity of oxalic acid may vary according to the quantity of water used. It will be found that the Prussian blue that has undergone the process of digestion, as described, requires but a small quantity of oxalic acid to dissolve it: about one part of oxalic acid will dissolve six parts of Prussian blue, the weight taken before digesting in the acid. This will answer for a concentrated solution, but for a dilute solution more acid will be required.
(TO BE CONTINUED.)
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