The next step is the treatment of the juices expressed by the rollers and collected in the troughs that carry it onward. The operations are highly technical, and different methods are employed in different mills. The first operation is one of purification. The juice, as it comes from the rollers, carries such materials as glucose, salts, organic acids, and other impurities, that must be removed. For this, lime is the principal agent. The details of it all would be as tedious here as they are complicated in the mill. The percentages of the different impurities vary with the variation of the soils in which the cane is grown. The next step, following clarification, is evaporation, the boiling out of a large percentage of the water carried in the juice. For this purpose, a vacuum system is used, making possible a more rapid evaporation with a smaller expenditure of fuel. These two operations, clarification and evaporation by the use of the vacuum, are merely improved methods for doing, on a large scale, what was formerly done by boiling in pans or kettles, on a small scale. That method is still used in many parts of the world, and even in the United States, in a small way. For special reasons, it is still used on some of the Louisiana plantations; it is common in the farm production of sorghum molasses in the South; and in the manufacture of maple sugar in the North. In those places, the juices are boiled in open pans or kettles, the impurities skimmed off as they rise, and the boiling, for evaporation, is continued until a proper consistency is reached, for molasses in the case of sorghum and for crystallization in the case of plantation and maple sugars. There is an old story of an erratic New England trader, in Newburyport, who called himself Lord Timothy Dexter. In one of his shipments to the West Indies, a hundred and fifty years ago, this picturesque individual included a consignment of "warming pans," shallow metal basins with a cover and a long wooden handle, used for warming beds on cold winter nights. The basin was filled with coals from the fireplace, and then moved about between the sheets to take off the chill. He was not a little ridiculed by his acquaintances for sending such merchandise where it could not possibly be needed, but it is said that he made considerable money out of his enterprise. With the covers removed, the long-handled, shallow basins proved admirably adapted for use in skimming the sugar in the boiling-pans. But the old-fashioned method would be impossible today.