=142. Table for the Determination of Invert Sugar (Reducing Sugars) in the Presence of Sucrose.=—The method adopted by the Association of Official Agricultural Chemists is essentially that proposed by Meissl and Hiller.[108] Prepare a solution of the material to be examined in such a manner that it contains twenty grams of the mixed sugars in one hundred cubic centimeters, after clarification and the removal of the excess of lead. Prepare a series of solutions in large test tubes by adding one, two, three, four, five etc. cubic centimeters of this solution to each tube successively. Add five cubic centimeters of the mixed copper reagent to each, heat to boiling, boil two minutes and filter. Note the volume of sugar solution which gives the filtrate lightest in tint, but still distinctly blue. Place twenty times this volume of the sugar solution in a 100 cubic centimeter flask, dilute to the mark, and mix well. Use fifty cubic centimeters of the solution for the determination, which is conducted as already described, until the weight of copper is obtained. For the calculation of the results use the following formulas and table of factors of Meissl and Hiller:[109] Let Cu = the weight of the copper obtained; P = the polarization of the sample; W = the weight of the sample in the fifty cubic centimeters of the solution used for determination; F = the factor obtained from the table for conversion of copper to invert sugar; Cu ---- = approximate absolute weight of invert sugar = Z; 2 100 Z × ----- = approximate per cent of invert sugar = _y_; W 100P ------- = R, relative number for sucrose; P + _y_ 100 - R = I, relative number for invert sugar; Cu ---- = per cent of invert sugar. W Z indicates the vertical column, and the ratio of R to I, the horizontal column of the table, which are to be used for the purpose of finding the factor (F) for calculating copper to invert sugar. _Example_:—The polarization of a sugar is 86.4, and 3.256 grams of it (W) are equivalent to 0.290 gram of copper. Then: Cu 0.290 ---- = ----- = 0.145 = Z 2 2 100 100 Z × ----- = 0.145 × ------ = 4.45 = _y_ W 3.256 100P 8640 -------- = ------------ = 95.1 = R P + _y_ 86.4 + 4.45 100 - R = 100 - 95.1 = 4.9 = I R : I = 95.1 : 4.9 By consulting the table it will be seen that the vertical column headed I = 150 is nearest to Z, 145, the horizontal column headed 95: 5 is nearest to the ratio of R to I, 95.1: 4.9. Where these columns meet we find the factor 51.2, which enters into the final calculation: