Summary and Conclusion.
1. Whereas many alkaloids give insoluble with ammonium- or potassium-sulphocyanide and zinc - sulphate, the double salts of quinine, cinchonine, cinchonidine, and cocaine are the most insoluble in the presence of excess of the reagents.
2. These double salts are exceedingly complex in their composition, a characteristic of many alkaloidal compounds. Thus, cinchonine-ammonium-zinc-sulphocyanide has the formula, 4 (C19H22N2O), 3 Zn (CNS)2, 2 NH4CNS, 4 HCNS. This corresponds closely with the formula of herepathite or sulphate of iodo-quinine, which may be written, 4 (C20H24N2O2), 3 H2SO4, 2 HI, 4 I2, + 3 aq.
3. Notwithstanding the complexity of these insoluble compounds, the determination of the amount of sulphocyanide required by the alkaloids for their formation serves as the basis of an accurate and speedy method of estimating quinine in the commercial drugs, and of assaying the crude cinchona-bark.
Experiments are now in progress to ascertain if this method may prove of value in estimating cocaine in the commercial preparations and in the assay of coca-leaves. With suitable modifications it may also serve as a means of separating different alkaloids, such as strychnine and brucine, or quinine and strychnine.
The above work was carried out in the Victoria College Laboratory, Wellington, under the conditions of the Jacob Joseph Scholarship.