83 



borrows from tiie corn starch side of the industry, the burr-stone 

 of the flour miller, modified for the treatment of wet grain, to 

 grind the root so that the ultimate cells of the root are ruptured 

 and torn apart. 



The second improvement is the adaptation of machinery used 

 in the extraction of precious metals from free milling ores. The 

 principle on which this works is that the rate of motion of bodies 

 falling freely in a fluid varies in accordance with the ratio of their 

 specific gravity to that of the fluid. The amount of friction de- 

 veloped varies with the size of the particles. If particles of 

 equal specific gravity, starch grains for instance, fall through an 

 upward-moving column of water, the fluid exercises a weighing 

 capacity, so that the starch grains, which are of uniform spe- 

 cific gravity and equal size, are separated from the particles of 

 cellulose and fiber constituting the bulk of the mass of the 

 finely-ground cassava roots. 



The finely-ground cassava pulp, falling through a vertical pipe 

 into a conical separator'* constructed somewhat on the principle of 

 an ore separator of the above type, is met by an ascending cur- 

 rent of water which carries the starch grains upwards through a 

 wire gauze diaphram, while the cellulose and fiber remain within 

 the cone. When the charge of pulp is exhausted it is discharged 

 automatically through the bottom of the cone and is ready to be 

 freed from its water, dried and baled for stock feed. 



The im.pure starch milk flows from the upper part of the 

 separator, and is conducted to' iron settling tanks with conical 

 bottoms. The milk flows down a tube to the bottom of the cone. 

 It then ascends in the increasing sectional area of the cone, in 

 which the liquid suffers reduction of velocity. The downward mo- 

 tion of the starch grains overcomes the upward motion of the fluid, 

 which continually flows away as dirty water through a pipe in the 

 upper part of the vessel, while the starch in a highly-concentrated 

 state is continually drawn off through a valve in the bottom of 

 the cone. The concentrated starch milk is then treated with 

 alkali, washed in shakers and run through a final battery of 

 purifying cones. The purified starch milk is run into vat^ and 

 the starch kept in suspension by means of agitators. From the 

 vats the milk runs into wooden boxes with perforated bottoms, 

 lined with muslin. These boxes are placed in a vacuum chamber 

 and the water extracted. The solid blocks of starch are then 

 cut, wrapped in paper and placed in a drving kiln, from which 

 the starch comes out as a marketable product. 



To make tapioca, the starch blocks taken from the boxes are 

 crushed and placed in a steam-jacketed cylinder and the steam 

 turned on. The heated starch grains burst, causing the starch 

 to assume the well-known form of tapioca. 



Where cassava is to be used in the manufacture of glucose the 



For fuller details, see Journ. Soc, Chem. Ind. 21, 4; and 22, 63. 



