Page:Popular Science Monthly Volume 19.djvu/267

Rh half the price of cane-sugar, this adulteration proves immensely profitable. The presence of grape-sugar in table-sugars can be approximately determined by several simple tests. When placed on the tongue, the bitter after-taste, already spoken of, may be detected. If spread in a thin layer on a piece of glass, and treated with a little water, the cane-sugar granules dissolve first, and the grape-sugar is left as a flocculent mass. With the microscope, its particles can be detected by the absence of all crystalline structure. Its exact quantity can only be determined by the polariscope. This is hardly a proper place to describe how this is done.

From the best information I can obtain, it appears that the cost of manufacture of glucose and grape-sugar is about one cent a pound. From twenty-six to thirty-two pounds are made from a bushel of corn. It is sold by the manufactories at three to four cents per pound. In the West the price of corn during the last year has averaged a little over thirty cents per bushel. It thus appears that the manufacture of glucose is a profitable industry.

I shall attempt here no detailed statement of the method of manufacture, but give only such an outline as may interest those who like to know how the things on their tables are prepared. The corn is first soaked for two or three days in warm water, and is then ground on specially prepared stones with a stream of water. The meal is next passed into a trough, the bottom of which is made of fine bolting-cloth. Here the starch is washed through, and led to large tanks, where it is allowed to settle. It is next beaten up with caustic soda to separate the gluten, and the starch is again allowed to settle in long, shallow troughs. The starch, washed from all adhering alkali, is next beaten up with water into a cream, and conducted into the converting-tubs. These tubs are supplied with coils of copper steam-piping and are made of wood. Here the starch cream is treated with dilute sulphuric acid, and steam is allowed to bubble up through the mixture from small holes in the copper pipes. This process of conversion, which is called "open conversion," is completed in about two hours.

Another method is called "close conversion." The substances are inclosed in stout copper cylinders, and subjected to the action of superheated steam. This process occupies about fifteen minutes.

The conversion is also accomplished sometimes by fermentation. This requires a much longer time. The greater part of it, however, is carried on by the method first named.

After conversion the acid is neutralized by marble-dust and animal charcoal. Since the sulphate of calcium, which is formed in this operation, is slightly soluble in water, carbonate of barium has been used instead of marble-dust. Its use, however, has not become general.

After neutralization the liquid is filtered through cloth and animal charcoal, and is then conveyed to the vacuum-pan. Here it is