In the preparation of starch from potatoes (potato starch) and other like vegetable substances, the roots or tubers, after being washed and peeled, either by hand-labour or by machinery, are rasped by a revolving grater, and the pulp washed on hair sieves until freed from feculous matter. Successive portions of the pulp are thus treated until the vessel over which the sieves are placed, or into which the washings run, is sufficiently full. The starch held in suspension in the water having subsided to the bottom, the water is drawn off, and the starch stirred up with fresh water, and again allowed to subside. This operation is repeated several times, with fresh water, until the starch is rendered sufficiently pure for commercial purposes, when it is washed and dried as before. The waste fibres and the washing waters are used as manure.

The starch manufactory at Hohenziatz treated 1216 tons of potatoes for starch between the 4th October, 1874, and the 6th February, 1875. The waste water after passing through precipitating vats, &c., for the purpose of collecting all the particles of starch, was conducted into a reservoir and mixed with spring water. This water was conducted over a meadow of 18·5 acres, and then passed to a meadow of 4·95 acres, and from this to the third and last, which contained 6·19 acres. The 29·64 acres received the water from 1064 tons of potatoes, or for each acre 4·38 cwt. of potash, 1·26 cwt. of phosphoric acid and 1·27 of nitrogen.

The following table shows analysis (1) of potato water; (2) of the same diluted; (3) of water from the first meadow; (4) water from the second meadow; 1 litre contained

—

1.2.3.4.
mg.mg.mg.mg.
Whole solid matter1857·8323·8322·8262·0
Organic matter1134·2101·838·078·8
Inorganic matter723·8222·0348·8183·2
Potash212·555·041·28·2
Phosphoric acid56·65·5tracetrace
Nitrogen140·712·04·09·1
Ammonia37·4000
Nitric acid3·8tracetracetrace

The disappearance of ammonia and phosphoric acid in 2 is accounted for by the precipitation of phosphate of magnesium and ammonium on the addition of the spring water.

The harvest in hay before the use of potato water was 19·13 cwt. per acre, and afterwards 31·88 cwt. The composition of the hay is better than before, as will be seen by the following comparative table:—

12
Moisture15·0015·00
Woody matter22·6622·88
Mineral matter7·648·69
Sol. in ether2·002·30
Albumen10·8915·85
Extractable matter not containing nitrogen41·8135·34
——————
100·00100·00[192]

[192] ‘Dingl. Polyt. Jour.,’ ccxxv, 394-396 (‘Journ. Chem. Soc,’).

In the manufacture of starch from rice and Indian corn (rice starch, maize starch), a very dilute solution of caustic soda, containing about 200 gr. of alkali to each gallon of liquid, is employed to facilitate the disintegration and separation of the gluten and other nitrogenised matters. A weak solution of ammonia, or sesquicarbonate of ammonia, is also similarly employed with advantage. The gluten may be recovered by saturating the alkali with dilute sulphuric acid. Such starch does not require boiling, and is less apt than wheat starch to attract moisture from the atmosphere. Most of the so-called ‘wheaten starch’ of commerce used by laundresses is now prepared from rice.