Fifty cubic centimeters of the solution are poured into a beaker and raised to a temperature of 55° in a constant temperature bath. Some brewers yeast amounting to about one-tenth of the total amount of sugar to be inverted, pressed in a towel, is thrown into the hot solution and the whole stirred until mixture is complete. The solution is left for four hours in the water-bath, at the end of this time it is cooled to 15°.5, a little freshly precipitated aluminum hydroxid added, and the volume made to 100 cubic centimeters. A portion of this solution is filtered and its polariscopic reading observed. The solution is then left till the next day, when another polariscopic reading is taken in order to prove that inversion is complete. The copper reducing power is also determined. The method of calculating the results is the same as when invertase is used. The following formulas are employed. _a_ = the number of divisions indicated by the polariscopic reading for a 200 millimeter tube: _aʹ_ = the same number after inversion: _m_ = the number of the divisions of the polariscopic scale which 200 millimeters of the sugar solution containing one gram of cane sugar per 100, alter at 15°.5 on being inverted: In the case of the ventzke polarimeter scale, one gram of cane sugar in 100 cubic centimeters, indicates +3.84 divisions and after inversion it gives -1.34 div. In experiments of this kind, therefore, _m_ = 5.18. _P_ = the weight of cane sugar present in 100 cubic centimeters of the original solution: The formula employed then is _a_ - 2_a_ʹ _P_ = -----------. _m_ For the copper reduction data the following are used: _G_ = the weight of 100 cubic centimeters of the original solution: _Gʹ;_ = the same for the inverted solution: Allowance must be made here both for the dilution and for the 5 per cent increase of the inverted sugar, but the latter number is so small that it need not be calculated accurately. _w_ = the weight of the original solution used for the estimation: _wʹ_ = the same factor for the inverted solution: _k_ = the weight of cupric oxid reduced by _w_: _kʹ_ = the same factor for _wʹ_: _p_ = the weight of cane sugar present in 100 cubic centimeters of the original solution: The formula to be employed then is _Gʹ kʹ G k_ _p_ = 0.4308(2 ------ - -----). _wʹ w_ This method has been applied to the estimation of cane sugar in molasses, apple juices and other substances. It is recommended by the authors as a simple and accurate means of estimating sucrose in all solutions containing it. The methods of making the copper reductions will be given hereafter.