886 



STARCH 





is exposed for two or three months to the air in summer, the starch is converted into 

 sugar, to the amount of one-third or one-half of its weight, into gum and gelatinous 

 starch, called amidine by De Saussure, with occasionally a resinous matter. This 

 curious change goes on even in close vessels. 



Starch from Potatoes. The potatoes are first washed in a cylindrical cage formed of 

 wooden spars, made to revolve upon a horizontal axis, in a trough filled with water to 

 the level of the axis. They are then reduced to a pulp by a rasping machine, similar 

 to that represented \nfigs. 1892, 1893 ; where a is a wooden drum, covered. with sheet 



iron, roughened outside with numer- 

 ous prominences, made from punching 

 out holes from the opposite side. It 

 is turned by a winch fixed upon each 

 end of the shaft. The drum is en- 

 closed in a square wooden box, to 

 prevent the potato-mash from being 

 scattered about. The hopper, b, is 

 attached to the upper frame, has its 

 bottom concentric with the rasp-drum, 

 and nearly in contact with it. The 

 pulp-chest, c, is made to slide out, so 

 as when full to be readily replaced 

 by another. The two slanting boards, 

 d, d, conduct the pulp into it. A 

 moderate stream of water should be 

 made to play into the hopper upon 

 the potatoes, to prevent the surface 

 of the rasp from getting foul with 

 fibrous matter. Two men, with one 

 for a relay, will rasp, with such a 

 machine, from 2 \ to 3 tons of potatoes 

 in 12 hours. 



The potato-pulp must be now elutriated upon a fine wire- or hair-sieve, which is set 

 upon a frame in the mouth of a large vat, while water is made to flow upon it from a 

 spout with many jets. The pulp meanwhile must be stirred and kneaded by the 

 hand, or by a mechanical brush-agitator, till almost nothing but fibrous particles are 

 left upon the sieve. These, however, generally retain about 5 per cent, of starch, 

 which cannot be separated in this way. This parenchyma should therefore be sub- 

 jected to a separate rasping upon another cylinder. The water, turbid with starch, is 

 allowed to settle for some time in a back ; the supernatant liquor is then run by a 

 cock into a second back, and after some time into a third, whereby the whole starch 

 will be precipitated. The finest powder collects in the last vessel. The starch thus 

 obtained, containing 33 per cent, of water, may be used either in the moist state, 

 under the name of green fecula, for various purposes, as for the preparation of dextrine 

 and starch-syrup, or it may be preserved under a thin layer of water, which must be 

 renewed from time to time, to prevent fermentation ; or lastly, it may be taken out 

 and dried. 



Washing apparatus have been contrived by Laine, Dailly, Huck, Vernies, Stolz, and 

 St.-Etienne. These are contrivances for working very large quantities of potatoes in 

 a short time. Buck's machine is stated to work 30,000 Ibs. of potatoes daily, and in 

 trials made with St.-Etienne's rasp and starch machinery, in Paris, which was driven 

 by two horses, nearly 18 cwts. of potatoes were put through all the requisite operations 

 in one hour, including the pumping of the water. The product in starch amounted to 

 from 17 to 18 per cent, of the potatoes. The quicker the process of potato-starch 

 making, the better is its quality. Volker proposed a process of rotting the potato to 

 separate the starch. 



Horse-chestnuts have been largely used at Nanterre, near Paris, in the manufac- 

 ture of starch. 



In the manufacture of potato-starch, a considerable quantity of the product is 

 lost, owing to the strong affinity which the starch has for the fibre of the potato. 

 M. Anthon stated some years ago that the manufacturer obtains only two-thirds of 

 the starch, the remainder being left in the pulp. He suggested that this third may 

 be utilised, by converting it into sugar by means of either malt or dilute sulphuric 

 acid. By employing 10 per cent, of the acid to the dry fibre, the saccharinVation is 

 complete in about two hours and a half ; but if only 3 or 4 per cent, of acid is used, 

 the boiling must be continued for at least 6 hours. Ten per cent, of malt effected the 

 conversion in 6 hours. Mr. Calvert has given the following analysis of the potato : 

 Water, 74 ; starch, 20 ; the remainder being fibrous, earthy, and alkaline matters. 



