240 72.9 74.5 70.6 86.6 81.3 245 74.8 76.4 72.5 88.9 83.4 250 76.7 78.4 74.4 91.2 85.5 255 78.6 80.5 76.5 93.5 87.6 260 80.5 82.8 78.8 95.9 89.8 265 82.5 85.1 81.1 98.3 92.2 270 84.7 87.5 83.5 100.7 94.6 275 87.1 89.9 85.9 103.3 97.1 280 89.7 92.4 88.6 106.1 99.6 285 92.3 94.9 91.3 109.0 102.3 290 95.1 97.6 94.2 112.0 105.1 295 98.0 100.4 97.2 115.1 107.9 298 100.0 102.5 99.0 117.0 109.5 VOLUMETRIC METHODS BASED UPON THE USE OF AN AMMONIACAL COPPER SOLUTION. =129. Pavy’s Process.=—The well-known solubility of cuprous oxid in ammonia led Pavy to adopt a copper reagent containing ammonia in the volumetric determination of reducing sugars.[95] In Pavy’s process an alkaline copper solution is employed made up in the usual way, to which a sufficient quantity of ammonia is added to hold in solution all the copper when precipitated as cuprous oxid. The solution used by Pavy has the following composition: One liter contains Crystallized copper sulfate 34.65 grams Potassium-sodium tartrate 173.00 ” Caustic potash 160.00 ” For use 120 cubic centimeters of the above reagent are mixed with 300 of ammonia of specific gravity 0.88, and the volume completed to one liter with distilled water. Twenty cubic centimeters of this reagent are equivalent to ten milligrams of dextrose or invert sugar when added in a one per cent solution. In the use of ammoniacal copper solution, care must be taken that all the liquids employed be entirely free of oxygen and that the contents of the flask in which the reduction takes place be in some way excluded from contact with the air. Pavy secured this by conducting the reduction in a flask closed with a stopper carrying two holes; one of these served for the introduction of the burette carrying the sugar solution and the other carried a tube dipping into a water seal by means of a slit rubber tube, which would permit of the exit of the vapors of steam and ammonia, but prevent the regurgitation of the water into the flask. The complete decoloration of the copper solution marks the end of the reaction. The usual precautions in regard to the length of the time of boiling must be observed.