THE POTATO AND ITS COMMERCIAL PRODUCTS. 337 



The manufacture of starch from potatoes is carried on to a very large 

 extent in France, not less than 27,000,0001b. being produced there 

 annually : from 50,000 to 60,000 tons of potatoes are used for this purpose 

 in the neighbourhood of Paris. In this country also potato-starch has of 

 late been manufactured in considerable quantity, and sold for food under a 

 variety of imposing names. Some of the starch sold as Indian corn starch 

 is usually potato-starch, with various slight additions to impart a flavour. 

 The potato flour and English arrowroot met with in many Italian ware- 

 houses in London are the same substance. 



The operations for extracting the starch from the potato are as follows : 

 1st. Washing the tubers. 

 2nd. Reducing them to a pulp, by rasping. 

 3rd. Pressing the pulp. 

 4th. "Washing the rough starch. 

 5th. Draining and drying the produce. 

 6th. Bolting and storing. 

 1st. The washing of the tubers requires particular attention, any dirt 

 left on them being injurious to the purity of the starch. The water itself 

 ought to be perfectly pure and clear. An open cylinder, working in a 

 trough into which a stream of water can be constantly pouring, is the best 

 method of effecting it. 



2nd. The rasping is accomplished by cylinders made of sheet-iron, 

 roughed by having holes thickly punched in it from the inside, so as to 

 form a grater. Or, if a more expensive and durable machine is required, 

 the cylinder is furnished with iron cutters set in wood. This is placed 

 under a hopper similar to that of a corn-mill. The cutting cylinder is made 

 to turn rapidly — say from 600 to 900 times per minute ; but the quicker 

 this is done, the more effectual will be the separation of the starch, &c. in 

 the tubers. The cylinder should be about 16 inches long, and 20 

 inches in diameter ; and such a one, revolving by means of multiplying 

 wheels 800 times per minute, will reduce 50 bushels of potatoes per hour 

 to a perfect pulp. It may be worked either by water, steam, horse, or hand 

 power. 



3rd. The pulping being effected, it is passed through a wire sieve ; and 

 the cellular tissues, which constitute the coarser parts, are separated, and 

 must be pressed, to extract from it what starch still remains. 



4th. Water is poured on the pulp whilst passing through the sieve. 

 This is run into vats, in which it is allowed to settle. When quite clear, 

 the water is poured off, and a fresh supply put on. 



5th. When the starch is perfectly clean, the water is finally poured off, 

 and the starch taken out, and laid on a clean floor, where it soon becomes 

 hardened and consolidated into a firm cake or mass. 



The sixth process finishes the operation, by breaking up the mass into 

 flour, and passing it through a bolting machine like those in a flour-mill, 

 which prepares it for sale. 



Any machinist is competent to fit up the necessary apparatus, either 



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