or Louisiana, but is carried out in Java and the Hawaiian Islands, where the sugar has to be shipped long distances for refining. The storage of undried raw sugar for long periods of time is a risky operation, as many speculators in sugar have found to their cost.

The sugar which is made from the pure juice of the cane is called "first sugar and the molasses drained from this sugar is called "first molasses." The latter still contains a large amount of sucrose, and various processes are used to recover as much of this as will crystallize. The first molasses is sometimes boiled down again in the vacuum pan and a second crop of sugar crystals obtained; this is the second sugar and the molasses obtained from this the second molasses. The second molasses may be boiled over again and a third sugar obtained, the molasses from which is the third or final molasses. Of course, as the sugar is removed the impurities become more and more concentrated in the molasses, until finally a thick stringy mass is obtained which will no longer crystallize. Such a molasses may still contain, however, 30 per cent sucrose; there is also present about 30 per cent invert sugar, 8 to 10 per cent of ash, and 8 to 10 per cent of gums, organic acids, amino compounds, etc.

The tendency of modern methods in cane sugar manufacture is against the repeated boiling of molasses, and the aim is to get as much sugar as possible in one operation. Many processes have been devised to attain this end. One method is to take the molasses from the first strike of sugar, draw this into the vacuum pan with the sirup for the succeeding strike, and boil the two down together. The masse cuite from this mixture is then run while still hot into large tanks, called crystallizers (Fig. 34), where it is kept in slow motion by means of revolving arms; as the mass cools and thickens more molasses is drawn to keep the proper degree of fluidity. When no more sugar will crystallize, as determined by analysis of samples, the contents

of the crystallizer are spun out in centrifugals and the molasses withdrawn from the factory.

Several of the features above described are shown in Fig. 35. In the foreground at the left are the large wheels of the cane mill; at the right is the conveyor which carries away the bagasse. In the background a multiple effect evaporator may be seen at the center, while slightly to the left is the condensing column, which extends through the roof. At the top of each of the condensing columns of the factory in which these photographs were taken is a small covered platform easily seen above the roofs in Fig. 36.

The process of manufacture described above yields "raw sugar," which is usually from 95 to 98 per cent pure. The removal of the remaining impurities constitutes the "refining" of the sugar and is usually carried on in places where fuel is more abundant than in the tropical countries where the sugar cane is chiefly cultivated, since about 25 pounds of coal are consumed in refining 100 pounds of sugar. The difference in price between raw and refined sugar is usually 0.7 to 0.9 cent per pound and the cost of refining is estimated at 0.6 to 0.65 cent per pound, leaving a margin of profit so small that it is necessary for the operation to be conducted on a large scale in order to make it remunerative. In the United States the industry. is carried on in a relatively small number of large establishments in or near the principal ports on the Atlantic and Pacific coasts.

Nearly all of the three million tons of sugar brought into the United States annually is refined in about 20 establishments. Thus the average output of the refineries now in operation is

1 Horne, School of Mines Quarterly, April, 1911.

2 At present (1913-1914) about three fourths of the sugar used in the United States is imported; that produced in the country (about one fourth) is for the most part refined at the point of production.

about 1,000,000 pounds of sugar per day each, some establishments having a much larger output than this.

In principle the refining process consists in washing off as much as is practicable of the molasses which adheres to the crystals of raw sugar, then dissolving the crystals, purifying and decolorizing the solution as thoroughly as possible, and recovering the sugar in a purified state by recrystallization. While the process is simple in principle, the large scale upon which it must be carried out and the extreme precautions necessary to guard against apparently small losses if the industry is to be economically successful require elaborate equipment and constant chemical control.

As the sugar, either in granular form or in solution, is passed through a number of operations in a continuous stream, it is found advantageous to build the refineries several stories high so that after the first lifting of the material its transportation from place to place for the successive steps of the processes may be effected chiefly by gravity.

The raw sugar is usually carried to the top of the building by means of a bucket elevator and washed by mixing with a small amount of sugar sirup and then separating in centrifugals, the sugar in the centrifugal being sometimes sprinkled with a little water for further purification.

After this washing the sugar usually has a purity of about 99, i.e. of the total solids in the moist sugar about 99 per cent is sucrose.

The sugar is then dissolved in hot water, this step being technically known as melting the sugar. The "melting" process is accomplished by running the sugar into water contained in steam-heated pans, the proportions and the heating being so regulated as to obtain a solution of 28 to 30° Baumé and a temperature of 150° to 170° F. A higher temperature might result in darkening the solution by slight decomposition of some of its constituents.

The hot solution then goes to the blowups for clarification, which is accomplished by adding a very small amount of acid calcium phosphate and then enough milk of lime to make the mixture neutral or very faintly alkaline. The precipitate thus formed carries down such impurities as gums and proteins, as well as suspended particles, and also removes a part of the coloring matter. The precipitate is removed by running the liquid through Taylor filters, which consist of twilled cotton bags about six feet long encased in strong, coarse-meshed hempen sheaths. A single filter box may contain 400 or more of these bags, each attached to the filter head by means of a metal bell and socket. The bags soon become clogged and so require frequent changing and washing; the wash water must be utilized in such ways as to avoid either a loss of sugar or a waste of fuel in evaporating more water than is necessary.

The filtrate from the bags is clear but not colorless. Most of the color is removed from this filtrate by passing it through boneblack filters. These are large, strong iron cylinders, often 10 feet in diameter and 20 to 30 feet high, filled with boneblack through which the sugar. solution flows very slowly, usually at about the rate of one foot per hour. On account of the immense amounts of boneblack required in a modern refinery, this part of the process requires very careful control in order to use the boneblack or "char" as economically as possible. Freshly charred boneblack removes the color from the sugar solution almost completely, but with accumulation of impurities in the pores of the char it naturally becomes less effective until finally the filtrate shows so much color that it must be re-treated and the boneblack must be washed and sent to the "char house " for reburning. Every reburning or "revivifying" leaves the pores of the boneblack somewhat clogged by the added carbon from the absorbed impurities, so that after 10 or 12 reburnings it is no longer economical to use. In the Weinrich oxidizing revivifier the reburning is carried out with a limited supply