After repeating the saturating process with the solution of carbonate of ammonia, drying and heating for a short time as previously described, the accuracy of the weight first obtained is again tested.
Estimation of silicic acid in the ash
3. Estimation of silicic acid in the ash: When examining cocoa powders and chocolate mass, the determination of the silicic acid content of the ash is sometimes a necessity, as this facilitates the detection of any shells which may have been added.[166] The ash of the cacao bean contains only between 0·25 and 1·0 percent of silicic acid, while that of the shell shows on analysis as much as 9 percent; it must, however, be taken into consideration that an unusually high value for silicic acid in the finished powder might be caused by impurities in the chemical or other agents used to effect the disintegration of the cacao. The signs of the presence of an extraordinary quantity of silicic acid are, according to C. R. Fresenius (Introduction to quantitative analysis)[167] a higher percentage of the ash itself than usual, and the quantity of ash used for the test should not be too small; it should further be remembered that certain cacao preparations, such as, for instance, the Dutch cocoa powders, contain large quantities of carbonic mineral matter, and the special treatment explained by Fresenius when dealing with such preparations separately should be applied.
Estimation of alkalis remaining
4. Estimation of alkalis remaining in cocoa powders. The ash obtained from 5 grammes of cocoa powder is washed out of the platinum pan into an ordinary water glass or tumbler, distilled water only being used for this purpose, afterwards finely crushed with a glass rod and heated to boiling point. The liquid is then allowed to settle, filtered and re-washed. At this stage 5 cubic centimetres of n/1 sulphurous acid are added, the liquid again heated to boiling point and titrated with 2/n or n/4 alkaline lye. In this way the quantity of added carbonic mineral matter is determined, in addition to the amount of carbonate present in ordinary cocoa powders, which is formed from the organic acid minerals when the ash is produced. Welmans has determined these values in the commonest varieties of beans and placed the results obtained at our disposal for the second edition of this book. These results are as follows:
a) Unshelled roasted beans
| Per cent. | Ariba I | Ariba II | Caracas I | Caracas II |
|---|---|---|---|---|
| Ash | 4·198 | 4·02 | 7·52 | 4·376 |
| Soluble in water | 1·698 | 1·66 | 1·34 | 1·676 |
| Insoluble in water | 2·5 | 2·36 | 6·18 | 2·70 |
| Alkali (considered as potash) | 0·6417 | 0·6417 | 0·596 | 0·9936 |
| Per cent. | Guayaquil | Trinidad | St. Thomé | |
| Ash | 5·12 | 3·6 | 3·92 | |
| Soluble in water | 2·11 | 1·565 | 1·604 | |
| Insoluble in water | 3·01 | 2·035 | 2·32 | |
| Alkali (considered as potash) | 0·84 | 1·125 | 0·67 |
b) Shelled, roasted beans:
| Per cent. | Puerto Cabello | Ariba I | Aribav II | Caracas I |
|---|---|---|---|---|
| Ash | 3·62 | 3·701 | 3·49 | 3·845 |
| Soluble in water | 1·72 | 1·423 | 1·315 | 1·76 |
| Insoluble in water | 1·90 | 2·273 | 2·175 | 2·08 |
| Alkali (potash) | 0·603 | 0·323 | 0·388 | 0·8725 |
| Alkali in powdered cacao with 33⅓ percent of fat calculated | 0·808 | 0·436 | 0·52 | 1·169 |
| Ash, calculated as above | 4·822 | 4·959 | 4·676 | 5·152 |
| Per cent. | Caracas II | Guayaquil | Trinidad | St. Thomé |
| Ash | 3·62 | 3·926 | 3·277 | 3·27 |
| Soluble in water | 1·62 | 1·476 | 1·727 | 1·34 |
| Insoluble in water | 2·00 | 2·45 | 1·55 | 1·93 |
| Alkali (potash) | 0·4478 | 0·402 | 0·4209 | 0·4048 |
| Alkali in powdered cacao with 33⅓ percent of fat calculated | 0·600 | 0·54 | 0·594 | 0·542 |
| Ash, calculated as above | 4·85 | 5·26 | 4·39 | 4·38 |
These tables show that: