THE SEPARATION OF THE CRYSTALS 



415 



dried. In sugar-house work the nature of the material varies usually in terms 

 of the " purity," but between material of the same purity much depends on 

 the skill of the sugar boiler, and on the nature of the impurities. Referring 

 to well-boiled massecuite of 75 purity or thereabouts, the time occupied 

 by the various operations will be approximately : Charging and accelerating, 

 one minute to two minutes, the time depending on the power available ; 

 running at speed, two to three minutes ; stopping, half a minute ; discharg- 

 ing, half a minute. The cycle, in all, occupies rather less than five minutes, 

 and at least twelve charges should be worked in an hour unless the masse- 

 cuite is badly boiled or unless the molasses is very viscous for reasons outside 

 the executive's control, as happens when operating on burnt cane. On 

 occasion, however, much greater capacities obtain ; with very free masse- 

 cuite and with the operatives stimulated to extraordinary exertion, as many 

 as twenty charges per hour can be obtained, provided there is sufficient 



FIG. 262 



power available to cut down the accelerating period to the lower limit. 

 In installing plant, however, it is seldom safe to calculate for more than eight 

 charges per hour. 



As regards low massecuites of 55 to 60 purity the cycle is quite different, 

 and is almost entirely occupied with running at speed. Fifteen minutes 

 as the over-all time taken for drying one charge is probably below the average, 

 and it is not advisable to reckon on more than three complete cycles to the 

 hour. 



Methods of driving Centrifugals. The standard method of driving 

 centrifugals is by belts. When the prime mover is a steam engine, the 

 latter is usually found making about 60 to 90 r.p.m., so that the ratio of gear- 

 ing between engine and machine will be about i to 20. The engine usually 

 drives a countershaft, which in turn transmits motion to a second shaft, 

 on which are mounted clutches, one for each machine in the battery. Occa- 



