Huck's sieve, Fig. 1287, is composed of three sieves a placed end to end, but sepa rated by cylindrical chambers b of greater diameter. The mesh of the sieves is of increasing degrees of fineness. The sieves rotate in the opposite direction to the brushes which impinge upon their surface, and to the iron arms in the intermediate cylinders. The paste from the rasper falls into the first sieve, where it is etrongly agitated by the brushes, while water is admitted by jets throughout the whole length of the sieve. In the intermediate cylinders b, the paste is stirred up with the water by the iron arms.
The sifted and washed starch is allowed to deposit itself in large tanks, and when this has sufficiently taken place, the water ie drained offi and the deposit is again washed with water. The milky liquid is drawn off in a thin stream and passed over an inclined plane, en which the starch deposita itaelf at varying distances from the head of the p/ane, according to its quality. It still requires a washing in clean water. Semetirnes centrifugal machines are employed. Fesca's is shown in plan in Fig. 1288; the drum o, made of Fin. sheet-iron, is dtiven by the belt b. Other centrifugal machines will be fiaind described under 131eaching (pp. 495-6) and Sugar.
Potato -starch is largely bleached by the application of sulphurio acid ; this being ab solutely requisite when tbe potatoes are at all decayed.
After the use ef the sulphuric acid, any possible remaining traces must be neutralized by ammonia or milk of lime, fixed caustic alkalies being inadmissible. Chlorine is also much used for bleaching starch, usually as a solution of calcium chloride in water soured by the addition of sulphuric acid ; this and some other salts cause the grains to swell, and render them soluble in eold water. Sal atnmeniac is another favourite agent.
The tnanufactured starch finally requires drying. This is primarily effected by spreading it on bricks or gypsum slabs, and then by laying it ou " hurdles " in a room which is thoroughly venti lated, and through which is passed air heated by a furnace beneath. An improved form of drying chamber by Laeambre and Persac is shown in Fig. 1289. The starch is introduced at a upon a series of linen trays b, all of which revolve at a uniform speed, so that the starch is gradually transmitted from one to the other till it reaches the receptacle c, having been completely dried in its passage by encountering the hot air derived from the furnace d.
According to Sehaer, potato-stareh when mixed with 10 parts by weight of a mixture of 2 parts hydrochloric acid sp. gr. I •I2 and I part water, forms a jelly which gives off a distinct odour Iike
that of French beans, by which it can easily be detected in presence of other starches.
(FR., Amidon de Riz ; GER., .Reisstarke).—The grain of the rice-plant (Oryza sativa) contains more starch than any other cereal, ranging between 75 and 85 per cent. The plant is raised in enormous quantities in irrigated fields in tropical and sub - tropical countries, notably India, China, Malaysia, Brazil, the S. States of America, and somewhat in Italy and Spain. Mere steeping and bruising do not suffice to sepo, rate the starch from the other components of the grain, and recourse is had to caustic alka line lyes for the purpose.
Orlando Jones' method is as follows. A Iye of caustic soda or potash is made of such a strength that 350 parts of water contain 1 of alkali ; 100 parts. of rice are steeped in 500 parts of this dilute lye, in a vessel of copper or tin-lined iron, fur nished near the bottom with a draw-off tap fitted with a gauze strainer. The liquor is drawn off after 21 hours, and twice the bulk of pure water is run in ; the whole is well stirred, and the water is again drawn off. The clean grain is drained through sieves, ground in a roller-mill or between millstones, and brushed through sieves, the coarse particles which refuse to pass being reground as often as necessary. The fine rice flour is next placed in a similar vessel to the first, with 10 times the quantity of alkaline lye, and the addition of auy solid matters which may have settled out from the water used to wash the whole grain ; 24 hours' agitation is then given to the mass, and it is allowed 70 hours' per fect rest for subsidence. The lowest lsyer formed consists of heavy mineral impulities, next follow the fragments of the broken hulls, and finally (top most) the starch, above which is a brownish-yellow turbid liquid contain ing the gluten in solution. This last is drawn off by a tin siphon when the operation is adjudged to be complete. The layer of starch is then mixed with water equal to twice the bulk of lye last used, the mass is allowed to sub side for an hour, and the milky fluid holding the starch is siphoned off through silken sieves into a series of large vats. The residues from the previous operation are treated again and again, to make thern yield the little staach they still contain. The milky liquid in the large vats deposits all its starch during 70 hours' rest. It is again washed with water, drained, and dried like wheat-starch.