I JO 



KXOWLEDGE lS: SCIENTIFIC NEWS. 



[November, 1905. 



admitted into the coils as the syrup covers them. 

 At the begrinningf boilini^f is very brisk, but as the con- 

 centration increases, it becomes slower. When the 

 boiler considers the concentration suflicient, he lessens 

 the supply of steam, and increases the vacuum, by this 

 means the temperature of the contents of the pan fall 

 to about 50°. The syrup is now supersaturated with 

 sugar, and crvstals commence to form. .\s soon as no 

 more sugar separates, more steam is admitted, and a 

 fresh quantity of syrup slowly drawn into the pan. 

 When the pan is full, the supply of syrup is stopped, 

 and the contents concentrated. Tlie exact concentra- 

 tion, or striking- point, has to be found l)y experience, 

 and is determined by the firmness, a sample taken out 

 of the pan by means of the proof-stick, acquires, when 



suddenly cooled in a pail ot cold water. 'l"he mixture of 

 crystallised sugar and molasses is now cooled, and 

 then, after being stirred in a mixer for some hours to 

 promote crystallisation, the porridge-like mass is centri- 

 fuged ; this process removes the molasses, and leaves 

 the hard crystals behind. The sugar is finally dried 

 in revolving iron cylinders fitted with steam coils. It 

 is then packed, and is ready for the market. 



Diffusion Prccess. — The principle of the diffusion 

 method is based on the property possessed by certain 

 bodies, when in solution, of passing through a mem- 

 brane ; if on the other side of the membrane, a liquid is 

 present, which contains a smaller quantity of the body 

 in question in solution. This process of diffusion will 

 ^o on until the concentration of the solution on botl 

 sides of the membrane is the same. Now, crystai- 

 lisable substances, such as sugar, have this property, 

 but gummy substances and albuminoid matter have not 

 this power, or possess it to a very small extent. The 

 process of diffusion is usually called dialysis. Now, in 

 the living cell of the sugar cane, the protoplasmic tegu- 

 ment of the cell is not a dialytic membrane, but if the 

 cell is killed, it then becomes a semi-permeable mem- 

 brane, i.e., is permeable to the one substance, but im- 

 pervious to the other. 



In the actual working of the diffusion process, the 

 protoplasmic cell is killed by heat. 'ITie process is 

 briefly as follows : The cane is cut up into small sec- 

 tions, which are placed into large vessels called c^iffu- 



sors, where hot water is poured upon them. The cells 

 are killed, and then the sucrose, glucose, the acids, and 

 certain inorganic substances diffuse through into the 

 water. .\.lter a lime, when a certain proportion of the 

 sugar has diffused out, the sugary water is run off, 

 and is replaced by a fresh quantity of water. 



The first diffusion juice is poured on to a fresh cjuaii- 

 tity of slices, and this process of drawing off and pour- 

 ing upon fresh slices is continued until the diffusion 

 liquor linally becomes so far enriched that no further 

 diffusion takes place. The juice so obtained is then 

 concentrated and treated in the same manner as already 

 described. The diffusion process is not used to any 

 great extent in the cane sugar industry, although a 

 very thorough exhaustion of the juice takes place. 



A great advantage with the mills is that their capa- 

 city permits greater variations of output than is the 

 case with tjie diffusion battery, l-'or example, it is 

 quite possible, in times of pressure, to crush as 

 much as 600 tons per day with a milling plant only con- 

 structed to crush 450 tons. There are, however, ad- 

 vantages in diffusion, the extraction is more thorough, 

 the juice is more casilv worked, because most of the 

 impurities remain in the bagasse, and finally there is less 

 danger of breakdown than in the case of machinery. 

 We will describe the diffusion process more exactly in 

 its applications to the beet sugar industry, w hi.rc it 

 plays a most important role. 



Exhausted Hlo/asses. — A question of considerable im- 

 portance to the sugar producer, is what to do with his 

 molasses, which remain after the sugar has been sepa- 

 rated, and from which a further quantity of sugar can- 

 not he profitably extracted. A certain proportion of 

 the better qualities can be used for treacle and golden 

 syrup, but the manufacturer finds great difficulty in 

 dealing with the major portion. If, in the neighbour- 

 hood, rum or arrach manufacture is carried on, then 

 I he most profitable outlet is to sell the molasses for 

 the preparation of spirits. 



The use of molasses as a fuel presents considerable 

 difficulties. If it is burnt mixed with the cane refuse, 

 at a comparatively low temperature, the charcoal 

 chokes the grate, whereas at high temperatures the 

 lime and other salts and the silica in the husks, form 

 a kind of glass, which blocks up the bars of the grate, 

 and prevents free access of air. In large factories 

 special furnaces are sometimes built. The molasses 

 are poured on an iron plate before the furnace, here 

 they dry, and arc then shovelled into the furnace. After 

 the fire is once lighted, it goes on without more fuel, 

 other than the dried molasses, and a fine ash, nearly 

 free from carbon, is obtained. The ash is very valuable 

 as a fertiliser, f>ecause it contains 35 per cent, of 

 pot;ish salts. It may also be used by glass-makers or 

 soap boilers. In fact, it often pavs to burn tlu- 

 molasses for the sake of its ash only. 



It mast be borne in mind that the process of manu- 

 facture here described is only concerned with produc- 

 ing Dcmarara or brown sugar. TTie further refining 

 to obtain a fine, white, loaf sugar is a separate process 

 altogether, and is not generally carried out in the 

 neighbourhood of the sugar plantations. Large re- 

 fineries are to be found, for example, in Liverpool and 

 Greenock. 



The m.-mufacture of sugar from the beet root will be 

 dealt with separately. 



The diagrams, with the exception of Fig. i, have 

 been taken from " The Technology of Sugar," by 

 [. fi. Mackinlr)sh ; I'ig. 1 from " (icscliiihtc des 

 Zuckers," by Lippmann. 



