On the front of the pan is a vertical row of windows made of heavy plate-glass, and through these the liquor is watched during the boiling. The massecuite in the pan is sampled at intervals by the sugar boiler, by means of a “proof stick,” a brass rod about three feet long and one and one-quarter inches in diameter, in the pan end of which there is a hollow space. This stick is pushed through an opening in the side of the pan into which it fits tightly, and then partly withdrawn. A small quantity of the contents of the pan remains in the hollow space, and this the sugar boiler removes and places on a piece of clear glass. On holding it up to the light, he sees exactly how the crystallization of the sugar is progressing, and by observing and feeling the crystals, he is enabled to control the boiling perfectly. When he concludes that the evaporation is complete and the massecuite of the proper consistency, the pump is stopped and the vacuum broken by opening a valve near the top of the pan, admitting the outside air. The foot valve is then opened and the massecuite drops from the pan into a mixer directly underneath. There it is kept constantly in motion by a revolving shaft with paddles, to prevent the crystals from sinking to the bottom. From the mixer it is drawn into the centrifugals and purged of the mother liquor, the pure crystals being left in the machine. The liquor thus drawn off contains whatever impurities may have remained in the original liquor. It is now pumped back and run through the char filters again, after which it is boiled in the vacuum pan and the granulated sugar taken out in the centrifugals. This completes the process of producing crystallized sugar by concentration. [Illustration: A REFINERY VACUUM PAN AND PUMP] [Illustration: ARRANGEMENT OF STEAM COILS IN A VACUUM PAN] There are many interesting and intricate problems in connection with the extraction of the sugar from the wash waters, sweet waters and low-grade syrups that are constantly accumulating in a sugar refinery, but space will not admit of their being dealt with here. Suffice it to say that the process of extraction is carried to a point where the sugar recovered barely pays for the labor and fuel expended in the operation. The ultimate result is white sugar, table syrup and molasses. This molasses is used largely in the manufacture of vinegar and alcohol. Mixed with grain and alfalfa meal, it makes an excellent stock food that cattle take to readily and that possesses high value as a fattening agent. The sucrose and glucose content of molasses as it leaves the refinery is about fifty per cent.