The impurities in yellow sugars are natural and consist of invert sugar, glucose, organic non-sugars and salts, all of which were originally present in the raws or were formed in the process of refining.
It is not unusual to hear it said that yellow sugars are sweeter than granulated. To the average palate this is apparently so, but, as has been shown, granulated sugar contains 99.8 per cent of sucrose or sweetening matter, while the highest grade of yellow carries only 92 per cent. Soft sugars dissolve more readily on the tongue than granulated, and the syrup or molasses in them accentuates their sweet taste.
There are several other grades of sugar prepared for the consuming market, but lack of space precludes a description of them or the methods by which they are produced.
MECHANICAL DEPARTMENT
It is needless to say that the conveying, melting, filtering, boiling, drying, screening, weighing and packing of one thousand tons of sugar in twenty-four hours necessitates a great amount of steam and a multiplicity of machinery.
The boilers generate steam to drive huge pumps that deliver cold salt water to the condensers throughout the refinery, to drive vacuum pumps that make boiling and evaporation in vacuo possible, and to drive large turbine or reciprocating engines that supply the electric power. The exhaust steam as it leaves the cylinders has a pressure of about fifteen pounds per square inch. It is conducted through pipes to the evaporators, pans, driers and tanks, where it is again used for concentrating the liquors, boiling in the pans, drying the sugar and keeping the liquors hot throughout the process. It leaves the various heating coils and tubes as hot water and is returned to the boilers for the generation of more steam.
Live steam, that is to say, steam just as it comes from the boilers, is used extensively in the vacuum pans for boiling the liquor to grain.
A refinery melting one thousand tons of raw sugar each day requires about 5500 boiler horse power. On the Atlantic coast coal is the fuel used, while on the Pacific coast oil is burned. The amount of fuel consumed in different refineries varies to some extent, but a fair average per ton of raw sugar melted is one and one-third barrels of oil, or one-third of a ton of coal.
In modern plants all the moving machinery, except the pumps and main engines, is usually driven by electric motors. This does away with many dangerous belts, as well as expensive transmission machinery. The motor drive is simple and efficient and therefore used extensively.
The mechanical department is under the general supervision of the superintendent, but in direct charge of a mechanical-electrical engineer. This man is known as the chief engineer, and he is directly responsible, not only for the operation of all the machinery in the plant together with its upkeep and repair, but he has also to cope with engineering problems that are constantly arising. Under his direction, a corps of draughtsmen is always busily engaged in planning and designing improvements and additions. He also maintains a force of mechanics, watching, operating and repairing the machinery. These men represent almost every trade, including machinists, blacksmiths, coppersmiths, tinsmiths, millwrights, boilermakers, riggers, masons, painters and many others.