180 



SUGAR. 



sities of saccharine solutions are affected by temperature, and the 

 changes of volume which take place in concentration being very 

 scanty, experiments were instituted to determine these points accu- 

 rately. It was found that at all densities a range of 4° Beaume 

 corresponded to a variation of 122° of temperature, and that the law 

 of variation in density due to change of temperature is the same as 

 in water. The alterations of volume caused by concentration also 

 followed closely those calculated from the specific gravity. Crystals, 

 separating from impure solutions, are always jDurer than the mother- 

 liquors ; hence the dark yellow mass sent down from the vacuum pans, 

 when drained from the uncrystallizable sugar and water associated 

 with it, leaves a crystalline mass more or less white behind. This 

 separation, technically called ' curing,' may be performed by simple 

 draining in vessels of suitable form, or, as in refineries, in moulds of 

 the familiar sugar-loaf shape, aided by suction : but on sugar estates 

 it is generally done in centrifugal machines. When the syrup is 

 good, the white crystals may be separated without washing of any 

 kind, but generally from a pint to a gallon of water or weak molasses 

 is thrown into each charge, to assist in washing the surfaces of the 

 crystals ; or the same object may be attained by projecting a jet of 

 high-pressure steam against the inside of the revolving ring of 

 sugar ; the steam, condensing, washes away the molasses, and at the 

 same time heats the mass and makes it dry more quickly when spread 

 out afterwards on the mixing floor. Yellow sugars are frequently 

 the pure crystals coated with more or less molasses, and therefore 

 when considering the relative yield of different factories, it is neces- 

 sary to know the quality of first sugars produced, as the loss in 

 washing yellow sugars white amounts to between 10 and 30 per 

 cent, of their weight. Dry white sugar runs like sand, but yellow 

 has a peculiar ' cling ' in it, due to the stickiness of the molasses. 

 The most difficult variety to produce is the bright canary-coloured 

 sugar, which can only be obtained from very pure bright syrups. 

 The mother-liquor, separated from the fii'st sugar, contains a con- 

 siderable quantity of crystallizable matter which separates again, as 

 in all crystallizing operations, by second concentration, and yields 

 the second sugars, which it is generally most profitable to leave in 

 the yellow state. The same remarks apply to third and fourth 

 boilings. 



" I have been able, with the assistance of the data obtained at 

 every step of the manufacture, to calculate the degree of concentra- 

 tion necessary in the trays to supply sufficient steam for the vacuum 

 pans and steam engines, and then to calculate the probable consump- 

 tion of fuel per ton of sugar. By means of the indicator diagrams, 

 it has been ascertained that the vacuum and centrifugal engines work 

 at 108 collective I.H.P., and as they do not work expansively, and 

 there must be considerable loss from condensation in the large steam 

 pipes, they probably consume 60 lbs. of steam at 3 lbs. pressure 

 per I.H.P. per hour. To supply these engines, therefore, would 

 involve the evaporation of 541 gallons of water per hour in the 

 concentrators. Supposing the factory to be in full work, each mill 

 producing 1500 gallons of juice, that is, 6000 gallons per hour at 



