The object to be attained in boiling white sugars is the separation of the crystallizable sucrose contained in a given solution from the impurities, moisture and non-crystallizable content of that solution. The formation of sugar crystals is a natural result of the evaporation of the moisture from the liquor or solution. In order to obtain pure white crystals, it is vitally essential that, as far as possible, all impurities and non-sugars, except water, be removed from the liquor before the boiling takes place, for if the coloring matter is not thoroughly taken out, obviously the crystals will be colored. The purifying and decolorizing operation is accomplished in the char filters. After the grain is once formed in definite crystals, these crystals attract and appropriate the sucrose in solution in the process of building up their structure, while repelling or excluding the impurities, so that in consequence the latter remain in solution. Irrespective, however, of whether crystallization of sucrose takes place in solutions of high or low purity, it will only partially remove the sucrose from the solution in one operation, the limit being fixed by the amount and nature of impurities present. In order to bring about further crystallization of sucrose the solution or mother liquor surrounding the crystals must be separated from them and be again diluted, filtered and concentrated. Briefly, the procedure in boiling white sugar in a vacuum pan is to take liquors of the highest purity for the first boiling. After the first crystals have been removed from the mother liquor in the centrifugal machines, the liquor is again diluted, decolorized by bone-char and boiled to grain. This operation is continued a number of times, the purity of the liquor decreasing each time. Finally, when the purity of the liquor falls to a certain point, the boiling is discontinued, for at this point conditions do not admit of further formation of pure sucrose crystals, and, if the process were pursued further, the resulting sugar would not be white. Therefore, when this state is reached, these low-grade liquors are boiled into a semi-refined sugar, commonly called “refinery raw,” which corresponds fairly closely in test with the original raw sugar, or they are used for making soft yellow sugars as explained later on. This refinery raw is then washed, melted and put through the whole process all over again. The liquor, from which the crystals formed in repeated boilings have been removed as made, at length becomes so charged with impurities that further crystallization of sucrose is impossible and this residue, or final waste, is known as blackstrap molasses. This manner of boiling white sugar has been called the “out and out” method, in contradistinction to the “in and in” method employed in boiling soft yellow sugars, of which a few words of explanation now follow.