221 



the juices of the tubers and the starch granules, a certain amount of 

 mud and fine particles of fibre and cell-tissue. 



Since the sand, starch and the cell-particles are heavier than 

 water they gradually sink and the remaining impurities can be 

 removed by drawing off the liquid. This process is carried out 

 either by sedimentation direct or by a process of running water. 



In the former process, vessels 3 or 4 feet in height are used. 

 After 8 or 10 hours the starch has settled, the water is run off and 

 the starch dug out from the bottom with spades. 



In the flooding system, a stream of starch water flows over a 

 level wooden channel 5 feet wide, 18 inches deep and 60 or more 

 feet in length. 



By this means the greater portion of the starch separates in a 

 purer state than in the sedimentary process, while the lighter and 

 smaller starch granules pass off with the impurities. The starch 

 from the outflow is subsequently recovered by letting the liquid 

 stand in suitable vessels. 



The crude starch is a yellowish, brown or red mass which 

 should be quite hard and firm. 



This first product is far from pure and is now passed through 

 the process of 



(6) Purificatio7i.~Th.\s is generally carried out by working up the 

 crude starch into a ' milk' of about 18° Beaume and allowing it to 

 settle. After 6 to 10 hours the starch has settled as a hard, white 

 mass with a superficial stratum of a brown, slimy mass of impure 



starch. 



In most cases some treatment with sulphurous acid or bleaching 

 powder is carried out at this stage to whiten the final product. The 

 impure surface layer is removed for further treatment while the 

 lower deposit is secured as the first product of the factory. 



Special processes for purifying the precipitated starch from the 

 waste waters and the slimy starch above described are resorted to 

 and a very considerable proportion of the starch set free is 

 finally secured as " superior" and " seconds." 



(8) D}'yi)ig the Starch. — This is generally carried out first by 

 centrifugals and then in special drying rooms. 



The Bye-Products. 



{a) The pulp. — This contains 88 to 97 per cent, of water. By 

 pressure the moisture can be reduced to about 25 per cent, and it 

 can then be fed to cattle direct or is dried by artificial heat and 

 sold as a dry cattle food. 



{b) The waste water. — This contains much plant food and can be 

 best used for the irrigation of the lands in the close vicinity of the 

 factory. 



The returns from a German starch factory. 



The following tables given by Dr. O. Saare* represent the effi- 

 ciency of starch manufacture in Germany under various conditions. 



♦Die Fiibrikatioii tier Kan oflel Slarke. 



