For the sake of uniformity, however, the copper solution should be boiled for a few minutes before the addition of the sugar in order to expel all oxygen, the sugar solutions should be made with recently boiled water and the precipitation of the suboxid should be accomplished by heating for just thirty minutes at 75°. At the end of this time an equal volume of cold, recently boiled, water should be added and the filtration at once accomplished. =122. Modified Permanganate Method.=—The permanganate method as used by Ewell, in this laboratory, is conducted as follows: After the precipitate is obtained, according to the directions given in the methods described, it is thoroughly washed with hot, recently boiled water, on a gooch. The asbestos, with as much of the precipitate as possible, is transferred to the beaker in which the precipitation was made, beaten up with from twenty-five to thirty cubic centimeters of hot, recently boiled water, and from fifty to seventy-five cubic centimeters of a saturated solution of ferric sulfate in twenty-five per cent sulfuric acid are added to the beaker and then poured through the crucible to dissolve the cuprous oxid remaining therein. If the precipitate be first beaten up with water as directed, so that no large lumps of it remain, there is no difficulty in dissolving the oxid in the ferric salt; while if any lumps of the oxid be allowed to remain there is great difficulty. After the solution is obtained, it is titrated with a solution of potassium permanganate of such a strength that each cubic centimeter is equivalent to 0.01 gram of copper. In triplicate determinations made by this method the precipitates obtained required after solution in the ferric salt, 28.7, 28.9, 28.6 cubic centimeters of potassium permanganate solution, respectively. For the quantities taken this was equivalent to an average percentage of reducing sugars of 4.19. The percentage obtained by the gravimetric method was 4.26. The method seems to be sufficiently accurate for all ordinary purposes and is extremely rapid. The permanganate solution used should be standardized by means of metallic iron, but in ordinary work it is also recommended to standardize by check determinations of reducing sugars in the same sample by the gravimetric method. =123. Determination of Reducing Sugar by the Specific Gravity of the Cuprous Oxid.=—Gaud proposes to determine the percentage of reducing sugar from the specific gravity of the cuprous oxid. The manipulation is carried out as follows: