=188. Polarization of Starch.=—Starch may be prepared for polarization by dissolving it in cold hydrochloric acid. The process as carried out by Effront is as follows.[153] Five grams of starch are rubbed with twenty cubic centimeters of cold concentrated hydrochloric acid for nearly ten minutes or until the solution is quite clear. The volume is completed to 200 cubic centimeters with water and the solution polarized. By this process there is always produced a notable quantity of reducing sugars, and for this reason it must be admitted that a portion of the starch has suffered complete hydrolysis. Ost therefore recommends the use of an acid of 1.17 specific gravity, and the gyrodynat of the soluble starch thus produced is found to vary from [_a_]_{D} = 196°.3 to 196°.7. When acid of 1.20 specific gravity is employed the gyrodynat falls to [_a_]_{D} = 194.2.[154] For approximately correct work the solution with the weaker hydrochloric acid and subsequent polarization is to be recommended as the most rapid method for starch determination. It will be of interest to add the observation that the gyrodynat of maltose has lately been redetermined by Ost, who finds it to be [_a_]_{D}²⁰ ° = 137°.04 ± 0.19.[155] =189. Solutions of Starch at High Pressure.=—Starch may also be brought into a condition suited to polarization by dissolving in water at a high temperature and pressure. The solution is accomplished in an autoclave as described in =181=. From two to three grams of starch are used and from eighty to ninety cubic centimeters of water. The starch is first reduced to a pasty state by heating with the water and, when evenly distributed throughout the flask, is rendered soluble by heating from three to five hours in an autoclave at from two to three atmospheres. The material is entirely without action on an alkaline copper solution. After heating, the volume of the solution is completed to 100 cubic centimeters and it is then polarized. The gyrodynat of starch dissolved in this way varies from [_a_]_{D} = 196°.5 to 197°.[156] Starch is prepared by Baudry for polarization by boiling with salicylic acid.[157] The gyrodynat of starch dissolved in this way is [_a_]_{D} = 200°.25. =190. Polarization after Solution in Dilute Nitric Acid.=—Guichard recommends saccharification with ten per cent nitric acid (ten cubic centimeters strong acid, ninety cubic centimeters water).[158] This treatment, even after prolonged boiling, gives only a light straw color to the solution which does not interfere with its polarization with a laurent instrument. In working on cereals four grams of the finely ground material, in which the bran and flour are intimately mixed, are used.