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Strychnine has a characteristic, very bitter taste; it imparts this taste to even very dilute solutions; it is unaffected by sulphuric acid, but gives a purple-blue colour, changing to crimson and light red, when the edge of this solution is touched with dioxide of manganese, potassium bichromate, ferricyanide of potassium, or permanganate of potassium.
Prepare a fresh solution, as needed each day, by dissolving a crystal of potassium ferricyanide about the size of a pin's head in 25 cc. of distilled water. The salt should be carefully tested with ferric chloride for the presence of ferrocyanides, which give a blue color with ferric salts.
In case of need, the ferricyanide can be purified by adding to its solution a little bromine water and recrystallizing the compound. PROCEDURE. Fill one burette with each of the solutions, observing the general procedure with respect to cleaning and rinsing already prescribed. The bichromate solution is preferably to be placed in a glass-stoppered burette.
It is, in general, true that oxidizable substances are determined by !direct! titration, while oxidizing substances are determined by !indirect! titration. The important oxidizing agents employed in volumetric solutions are potassium bichromate, potassium permangenate, potassium ferricyanide, iodine, ferric chloride, and sodium hypochlorite.
A drop of the oxidized solution should be tested on a watch-glass with potassium ferricyanide, to insure a complete oxidation. The ionic changes which are involved in this oxidation are perhaps most simply expressed by the equation Even with this precaution the entire absence of sulphates from the first iron precipitate is not assured.
Of the methods of precipitating the compounds of the protoxide and estimating the acid, that of the phosphate is by far the most accurate, titrating with uranium solution; 99.82 is a nearly constant average with me, much depending on the operator's familiarity with the uranium process. The methods of Lenssen, or ferricyanide of potassium method, yields very widely differing results.
The action of strong hydrocholoric acid upon morphine changes it into apomorphine, C H NO , by the withdrawal of a molecule of water. Ferricyanide of potassium and caustic soda solution change morphine into oxidimorphine, C H N O . When heated with strong potassium hydrate, it yields methylamine. In this case, instead of opianic acid, its reduction product meconine, C H O , is produced.
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