It is easy to see that in the Pavy process the quantity of ammonia in the solution is rapidly diminished during the boiling and this has led to the suggestion of other methods to exclude the air. Among these have been recommended the introduction of a current of hydrogen or carbon dioxid. One of the best methods of procedure is that proposed by Allen, who recommends covering the copper solution by a layer of paraffin oil (kerosene).[96]
130. Process Of Peska.—Peska has also independently made use of Allen’s method of covering the solutions with a layer of paraffin oil and finds it reliable.[97] The copper reagent employed by him has the following composition:
| Crystallized copper sulfate | 6.927 | grams |
| Ammonia, twenty-five per cent strength | 160.00 | cc. |
The copper sulfate is dissolved in water, the ammonia added, and the volume completed to half a liter with distilled water. A second solution containing half a liter is made by dissolving 34.5 grams of potassium-sodium tartrate and ten grams of sodium hydroxid and completing the cool solution to half a liter with distilled water. In all cases the water used in making up the above solutions must be freshly boiled to exclude the air.
For the titration, fifty cubic centimeters of each of the above solutions are taken, mixed and covered with a layer of paraffin oil half a centimeter in depth. The reduction is not accomplished at a boiling temperature, but at from 80° to 85°. The manipulation is conducted as follows:
The mixed solutions are placed in a beaker, covered with oil, and heated to 80°. The temperature is measured by a thermometer which also serves as a stirring rod. The sugar solution is run down the sides of the beaker from a burette of such a shape as to be protected from the heat. After each addition of the sugar solution the mixture is carefully stirred, keeping the temperature at from 80° to 85°. The first titration is made to determine approximately the quantity of sugar solution necessary to decolorize the copper. This done, the actual titration is accomplished by adding at once the total amount of sugar solution necessary to decolorize, less about one cubic centimeter. Any sugar solution adhering to the side of the beaker is washed down by distilled water, the contents of the beaker well stirred, and the temperature kept at 85° for two minutes. The rest of the sugar solution is then added in quantities of one-tenth of a cubic centimeter until the decoloration is completed. The total time of the final titration should not exceed five minutes. The sugar solution should be as nearly as possible of one per cent strength. If a lower degree of strength be employed a larger quantity of the sugar is necessary to reduce a given quantity of copper.
In the case of dextrose, when a one per cent solution is used, eight and two-tenths cubic centimeters, corresponding to 80.2 milligrams of dextrose, are required to reduce 100 cubic centimeters of the mixed reagent. On the other hand, when the sugar solution is diluted to one-tenth of a per cent strength 82.1 milligrams are required.
With invert sugar slightly larger quantities are necessary, the reducing power being as 94.9 to 100 as compared with dextrose. With a one per cent strength of invert sugar it is found that eighty-four milligrams are required to reduce 100 cubic centimeters of the mixed reagent and when the strength of the invert sugar is reduced to one-tenth per cent 87.03 milligrams are required.
131. Method Of Allein and Gaud.—Allein and Gaud have proposed a further modification of the ammonia process which consists essentially in the suppression of rochelle salt and fixed caustic alkali and the entire substitution therefor of ammonia. Ammonia acts with much less vigor upon sugars than the caustic alkalies, and it is therefore claimed that the decomposition of the sugar due to the alkali is reduced to a minimum when ammonia is employed.[98] The copper solution is made as follows:
Dissolve 8.7916 grams of electrolytic copper in ninety-three grams of concentrated sulfuric acid diluted with an equal volume of water. Complete the resulting solution to one liter with concentrated ammonia. Ten cubic centimeters of this solution are equal to fifty grams of dextrose.