In most genuine honeys the value of _R_ between 0° and 88° is approximately thirty divisions of the cane sugar scale or 10° angular measure for 26.048 grams in 100 cubic centimeters, read in a 200 millimeter tube, or, for 13.024 grams in 100 cubic centimeters read in a 400 millimeter tube. The method of analysis outlined above has been applied in the examination of a large number of honeys with most satisfactory results. It can also be applied with equal facility to other substances containing levulose. =242. Sucrose and Dextrose.=—In mixtures these two sugars are easily determined by optical processes, provided no other bodies sensibly affecting the plane of polarized light be present. The total deviation due to both sugars is determined in the usual way. The percentage of sucrose is afterwards found by the inversion method (=92=). The rotation, in the first instance due to the sucrose, is calculated from the amount of this body found by inversion, and the residual rotation is caused by the dextrose. The percentage of dextrose is easily calculated by a simple proportion into which the numbers expressing the gyrodynats of sucrose and dextrose enter. When the readings are made on a ventzke scale the calculations are made as follows: Weight of sample used 26.048 grams. First polarization 88°.5 Polarization after inversion 10°.5 Temperature 20°.0 Percentage of sucrose 58.4 Rotation due to dextrose 30°.1 Percentage of dextrose: 66.5 : 53 = _x_ : 30.1; whence _x_ = 37.8. The sample examined therefore contains 58.4 per cent of sucrose and 37.8 per cent of dextrose. It is evident that the method just described is also applicable when maltose, dextrin, or any other sugar or polarizing body, not sensibly affected by the process of inversion to which the sucrose is subjected, is substituted for dextrose. When, however, more than two optically active bodies are present the purely polariscopic process is not applicable. In such cases the chemical or the combined chemical and optical methods described further on can be employed. =243. Lactose in Milk.=—By reason of its definite gyrodynat lactose in milk is quickly and accurately determined by optical methods, when proper clarifying reagents are used to free the fluid of fat and nitrogenous substances. Soluble albuminoids have definite levogyratory powers and, if not entirely removed, serve to diminish the rotation due to the lactose. Milk casein precipitated by magnesium sulfate has the following gyrodynatic numbers assigned to it:[199] Dissolved in water [_a_]_{D} = -80° ” ” very dilute solution [_a_]_{D} = -87°. ” ” dilute sodium hydroxid solution [_a_]_{D} = -76°. ” ” strong potassium hydroxid solution [_a_]_{D} = -91°.