The determination of the ~refractive index~ in Zeiss butyrorofractometer is of value for ascertaining the purity of cacao butter, and it serves as a control on the iodine value, for according to Roques[43] the refractive index and the iodine value stand in equal relation, so that fat having a high refractive index gives a high iodine value and vice versa. The refractive index of cacao butter ranges between 1·4565-1·4578 at 40°C. corresponding to 46-47·8 on the scala of the Zeiss butyro-refractometer. The use of the latter is recommended by Filsinger as a preliminary test for cacao butter, since with a normal refraction it is not necessary to proceed further and determine the iodine, saponification and acid values, nor the melting point. In conclusion we annex table 12, where the respective constants for different varieties of cacao butter will be found tabulated.[44] For further information on all these methods, the reader is referred to the excellent work of R. Benedict, entitled “Analysis of Fats and Waxes”: VII. Edition, Berlin. ~Table~ 12. Physical and Chemical Analyses of the Various Kinds of Pressed Stollwerck Cacao Butter. ======================+=======+=======+=======+========+=======+ | Accra | Ariba | Bahia | Guay- |Cam- | | | | | aquil | eroon | | | | | | | ======================+=======+=======+=======+========+=======+ | | a) ~Fat~ Point of refraction | | | | | | at 40° C | 64·3 | 46·1 | 46·9 | 46·5 | 46·0 | Melting Point | | | | | | (Polenske)(1) | 33·1 | 33·2 | 31·95 | 32·5 | 33·65 | Freezing Point | | | | | | (Polenske) | 20·0 | 21·55 | 19·35 | 19·8 | 20·95 | Variations(2) between| | | | | | Melting Point and | | | | | | Freezing Point | | | | | | (Polenske) | 13·1 | 11·65 | 12·60 | 12·5 | 12·70 | Reichert-Meissl number| 0·49 | 0·33 | 0·38 | 0·55 | 0·33 | Polenske(2) number | 0·50 | 0·50 | 0·60 | 0·42 | 0·40 | Köttstorfer number |192·4 |191·7 |191·4 |190·8 |193·2 | Hübl’s iodine value | 35·24 | 34·89 | 37·87 | 36·54 | 34·0 | Bellier’s reaction(4) | violet| as 1 | as 1 | as 1 | as 1 | R. Cohn’s reaction(5) | | | | | | a) Fresh fat(6) |neg- | “ | “ | “ | “ | |ative | | | | | b) Rancid fat |strong |weak |pos- |weak |pos- | |pos- |pos- |itive |pos- |itive | |itive |itive | |itive |