MECHANICS AND USEFUL ARTS. 97 



are to be traced many of the fatal mistakes at present connected with 

 the manufacture of sugar. 



Thus, while the temperature of the syrup during ebullition in a 

 vacuum pan indicates as low perhaps as 180 Fahr., the copper 

 worm, against which portions of the sugar are constantly brought into 

 contact, "is equal to and often above 220 Fahr.; the consequence 

 of which is the destruction of the color, and an injury to the crystal- 

 lizing powers of the sugar. By an arrangement which Mr. Bessemer 

 terms a hot air evaporator, the concentration of saccharine fluids may 

 now, however, be effected without the slightest injury to color or 

 quality, and in an increased quantity. 



Thi's apparatus consists of a tank of thin plate iron, of about 10 

 feet by 8 feet, and 2.1 feet in depth, which has a false bottom, curved 

 so as to form two parallel segments of a cylinder. Above these and 

 coincident with them is a hollow drum of 18 inches in diameter, 

 mounted on an axis, and upon which is formed a broad spiral blade in 

 the shape of a screw, or " creeper," the thread of which is about 

 fifteen inches in depth, and the convolutions three-quarters of an inch 

 apart ; and between each of the blades or threads of the screw, holes 

 are formed spirally from one end of the drum to the other. At one 

 end of the hollow drum, air, supplied by a blowing fan, and heated to 

 150 by passing along a flue, is made to enter, which escapes through 

 the holes in the drum in a radical direction, and sweeps like the hot 

 breath of the simoon over the wet surfaces of the various revolving 

 blades, absorbs the moisture thus exposed to its action, and passes oif 

 in an invisible vapor. Upwards of six thousand square feet of evap- 

 orating surface is thus obtained in the small space of 10 feet by 8 feet. 

 The screws make about eight revolutions per minute, and as they 

 revolve, the more concentrated portions of the fluid are washed off 

 as they descend into the fluid, and fresh portions are being constantly 

 brought up on the surface of the screw, to be in like manner sub- 

 jected to the hot-air blast. Finally, after three or four hours, the 

 whole of the surplus liquor is carried off; the remaining fluid is 

 sufficiently concentrated, and assumes a thick gelatinous appearance ; 

 and the screw, made to revolve in the opposite direction, expels the 

 solution from the tank ready for the process of crystallization. By 

 this process the sugar is not at any time exposed to a hotter surface 

 than 140. Xo boiling, consequently, takes place, no slea is formed, 

 and not one grain of crystallizable sugar is converted into molasses. 

 The entire cost of fuel for evaporation is saved, the waste heat of the 

 chimney and waste steam of the engine being alone employed, and 

 the apparatus costs less than the ordinary vapor pans; it can be 

 worked with a small amount of wind or water power. Three hogs- 

 heads of sugar, it is stated, can be obtained where two only are now 

 produced, whilst the quality will be superior in color and taste, and 

 will be perfectly free from molasses. 



The separation of the crystals from the mother liquor in which they 

 are found is effected in a most ingenious and efficient manner by the 

 use of the air pump. The transformation from the most repulsive 



