This reagent undergoes no change when kept for a long while, especially in large vessels. Even in smaller vessels it can be kept for a year or more without undergoing any change.
The method of analysis is the same as that described in paragraph [128], with the exception that the boiling is continued for only five minutes instead of ten, and the quantities of the copper and sugar solutions used are doubled, being 100 and fifty cubic centimeters respectively. In no case must the solution used contain more than thirty-eight milligrams of invert sugar. The quantity of sucrose in the mixture is obtained by polarization ([94]). Ost has also recalculated the reduction values of the common sugars for the strong copper carbonate solution, and the numbers obtained are slightly different from those given on [page 142].[190]
For different percentages of invert sugar in mixtures of sucrose, the quantities of invert sugar are calculated from the number of milligrams of copper obtained by the following table:
- (A) = Milligrams of copper obtained.
- (B) = Pure invert sugar.
- (C) = Invert sugar.
- (D) = Sucrose.
| Milligrams of Invert Sugar in Mixtures of | ||||||||
|---|---|---|---|---|---|---|---|---|
| 5(C) | 2(C) | 1.5(C) | 1.0(C) | 0.8(C) | 0.6(C) | 0.5(C) | ||
| (A) | (B) | 95(D) | 98(D) | 98.5(D) | 99.0(D) | 99.2(D) | 99.4(D) | 99.5(D) |
| 88 | 37.9 | 37.1 | 36.0 | 35.4 | 34.7 | 34.2 | 33.9 | 33.6 |
| 85 | 36.3 | 35.5 | 34.5 | 34.0 | 33.4 | 32.9 | 32.5 | 32.2 |
| 80 | 33.9 | 33.0 | 33.2 | 31.7 | 31.2 | 30.7 | 30.2 | 29.9 |
| 75 | 31.6 | 30.7 | 30.0 | 29.5 | 29.0 | 28.5 | 28.1 | 27.7 |
| 70 | 29.4 | 28.5 | 27.8 | 27.4 | 26.8 | 26.4 | 25.9 | 25.6 |
| 65 | 27.3 | 26.3 | 25.7 | 25.3 | 24.7 | 24.3 | 23.8 | 23.5 |
| 60 | 25.2 | 24.2 | 23.6 | 23.2 | 22.6 | 22.2 | 21.8 | 21.5 |
| 55 | 23.1 | 22.1 | 21.6 | 21.2 | 20.6 | 20.2 | 19.8 | 19.6 |
| 50 | 21.2 | 20.1 | 19.6 | 19.2 | 18.6 | 18.3 | 17.9 | 17.7 |
| 45 | 19.3 | 18.2 | 17.6 | 17.2 | 16.7 | 16.3 | 16.0 | 15.8 |
| 40 | 17.3 | 16.3 | 15.7 | 15.3 | 14.8 | 14.5 | 14.2 | 14.0 |
| 35 | 15.4 | 14.5 | 13.8 | 13.4 | 13.0 | 12.7 | 12.5 | 12.3 |
| 30 | 13.5 | 12.6 | 12.0 | 11.6 | 11.2 | 11.0 | 10.8 | 10.6 |
| 25 | 11.5 | 10.8 | 10.3 | 10.0 | 9.5 | 9.3 | 9.1 | 9.0 |
| 20 | 9.6 | 9.1 | 8.6 | 8.3 | 7.9 | 7.7 | 7.5 | 7.3 |
| 15 | 7.7 | 7.3 | 6.9 | 6.7 | 6.3 | 6.1 | 5.8 | 5.6 |
| 10 | 5.8 | 5.4 | 5.1 | 5.0 | 4.7 | 4.5 | 4.2 | 3.9 |
| Milligrams of Invert Sugar in Mixtures of | ||||||
|---|---|---|---|---|---|---|
| 0.4(C) | 0.3(C) | 0.2(C) | 0.1(C) | 0.05(C) | 0.02(C) | |
| (A) | 99.6(D) | 99.7(D) | 99.8(D) | 99.9(D) | 99.95(D) | 99.98(D) |
| 88 | 33.3 | |||||
| 85 | 32.0 | 31.8 | ||||
| 80 | 29.7 | 29.5 | ||||
| 75 | 27.4 | 27.2 | ||||
| 70 | 25.3 | 25.0 | ||||
| 65 | 23.2 | 22.8 | ||||
| 60 | 21.2 | 20.8 | 20.4 | |||
| 55 | 19.3 | 18.9 | 18.5 | |||
| 50 | 17.4 | 17.0 | 16.7 | |||
| 45 | 15.6 | 15.3 | 14.9 | |||
| 40 | 13.8 | 13.5 | 13.2 | |||
| 35 | 12.1 | 11.9 | 11.5 | 10.3 | ||
| 30 | 10.4 | 10.2 | 9.9 | 8.8 | ||
| 25 | 8.8 | 8.6 | 8.2 | 7.3 | ||
| 20 | 7.1 | 6.9 | 6.6 | 5.8 | 4.9 | |
| 15 | 5.4 | 5.2 | 5.0 | 4.4 | 3.7 | 2.0 |
| 10 | 3.8 | 3.5 | 3.4 | 3.0 | 2.5 | 1.7 |
234. Soldaini’s Method Adapted to Gravimetric Work.—By reason of their better keeping qualities and because of their less energetic action on non-reducing sugars, copper carbonate solutions are to be preferred to the alkaline copper tartrate solutions for gravimetric determinations of reducing sugars in cane juices and sugar house products, provided the difficulties which attend the manipulation can be removed. Ost has succeeded in securing perfectly satisfactory results with copper carbonate solution by slightly varying the composition thereof and continuing the boiling, for the reduction of the copper, ten minutes.[191] The copper solution is made as follows:
| 17.5 | grams | crystallized copper sulfate. |
| 250.0 | ” | potassium carbonate. |
| 100.0 | ” | ”bicarbonate. |
The above ingredients are dissolved in water and the volume of the solution completed to one liter. The object of the potassium bicarbonate is to secure in the solution an excess of carbon dioxid and thus prevent the deposition of basic copper carbonate on keeping. The manipulation is conducted as follows:
One hundred cubic centimeters of the copper solution are mixed with half that quantity of the sugar solution in a large erlenmeyer, which is placed upon a wire gauze, heated quickly to boiling and kept in ebullition just ten minutes. The sugar solution should contain not less than eighty nor more than 150 milligrams of the reducing sugar, and the quantity of the solution representing this should be diluted to fifty cubic centimeters before mixing with the copper solution. After boiling, the contents of the erlenmeyer are quickly cooled and filtered with suction through an asbestos filter and the whole of the copper suboxid washed into the filter tube. This precipitated suboxid is washed once with a little potassium carbonate solution then with hot water and finally with alcohol, well dried, heated to redness, and the copper oxid obtained reduced to metallic copper in an atmosphere of hydrogen entirely free of arsenic. From the weight of metallic copper obtained the quantity of sugar which has been oxidized is calculated from the tables below.