IV.—METHODS OF MANIPULATION.
The methods of manipulation used in the polarization of sugar are of prime importance. They consist in weighing out the sugar, dissolving it, clarifying the solution, making it up to standard volume, filtering, filling the observation tube, regulating the illumination, and making the polariscopic reading.
The proper conduct of these processes, in connection with the use of accurately graduated apparatus, is the only surety against the numerous sources of error which may be encountered. Different sugars require different treatment in clarification, and much must necessarily be left to the judgment and experience of the operator.
The following directions are based upon various official procedures such as the one used in the United States custom houses, the method prescribed by the German government, etc. They embody also the result of recent research in regard to sources of error in polarimetric estimation of sugar: