=133. Sidersky’s Modification of Soldaini’s Process.=—In all cases where the sugar solutions are not too highly colored, Sidersky finds that the method of reduction in a large test tube, as practiced by Violette, is applicable with the copper carbonate solution.[101] For more exact work it is preferred to determine the quantity of copper reduced by an indirect volumetric method. The sugar solution, properly clarified and the lead removed if subacetates have been used, is made of such a volume as to contain less than one per cent of reducing sugars. In a flask or large test tube are placed 100 cubic centimeters of the copper solution, which is boiled for a short time and the sugar solution added, little by little, from a pipette, at such a rate as not to stop the ebullition. The boiling is continued for five minutes after the last addition of the sugar. The vessel is taken from the flame and 100 cubic centimeters of cold water added, the whole brought on an asbestos felt and the cuprous oxid washed with hot water until the alkaline reaction has disappeared. The residual cuprous oxid is dissolved in a measured quantity of set sulfuric acid, semi- or fifth-normal, a few particles of potassium chlorate added, and the mixture boiled to convert any cuprous into cupric sulfate. The reaction is represented by the following formula: 3Cu₂O + 6H₂SO₄ + KClO₃ = 6CuSO₄ + KCl + 6H₂O. The residual sulfuric acid is titrated with a set alkali in excess, ammonia being preferred. The solution of ammonia is made by diluting 200 cubic centimeters of commercial aqua ammonia with 800 of water. Its strength is determined by adding a little copper sulfate solution as indicator and then the set solution of sulfuric acid until the blue color disappears. The copper sulfate secured from the cuprous sulfate as described above is cooled, and a quantity of the ammonia, equal to twenty-five cubic centimeters of the set sulfuric acid, added. The excess of the ammonia is then determined by titration with the sulfuric acid, the disappearance of the blue color being the indication of the end of the reaction. The number of cubic centimeters of the set sulfuric acid required to saturate the ammonia represents the equivalent of cuprous oxid originally present. One cubic centimeter of normal sulfuric acid is equivalent to 0.0317 gram of metallic copper. To determine the weight of invert sugar oxidized, multiply the weight of copper, calculated as above described, by the factor 0.3546.[102] For a general application of this method of analysis the relative quantities of copper reduced by different quantities of sugar must be taken into consideration.