(see Encycl.) is commonly made of wheat, and the very best starch can perhaps be made of nothing else. Wheat, however, is too valuable an article of food to be employed as the material of starch, when any thing else will answer the purpose; and it has long been known that an inferior kind of starch may be made of potatoes. Potatoes, however, are themselves a valuable article of food; and it is therefore an object of importance to try if starch may not be made of something still less useful.
On the 8th of March 1796, a patent was granted to Lord William Murray for his discovery of a method by which starch may be extracted from horse-chestnuts. That method is as follows:
Take the horse-chestnuts out of the outward green prickly husks; and then, either by hand, with a knife or other tool, or else with a mill adapted for that purpose, very carefully pare off the brown rind, being particular not to leave the smallest speck, and to entirely eradicate the sprout or growth. Next take the nuts, and rasp, grate, or grind them fine into water, either by hand, or by a mill adapted for that purpose. Wash the pulp, which is thereby formed in this water, as clean as possible, through a coarse horse-hair sieve; this again wash through a finer sieve, and then again through a still finer, constantly adding clean water, to prevent any starch from adhering to the pulp. The last process is, to put it with a large quantity of water (about four gallons to a pound of starch) through a fine gauze, muslin, or lawn, so as entirely to clear it of all bran or other impurities. As soon as it settles, pour off the water; then mix it up with clean water, repeating this operation till it no longer imparts any green, yellow, or other colour to the water. Then drain it off till nearly dry, and set it to bake, either in the usual mode of baking starch, or else spread out before a brisk fire; being very attentive to stir it frequently to prevent its burning, that is to say, turning to a paste or jelly, which, on being dried, turns hard like horn. The whole process should be conducted as quickly as possible.
Mention is here made of a mill which may be employed to grind the horse-chestnuts; but none is described as proper for that purpose. Perhaps the following mill, which was invented by M. Baume for grinding potatoes, with a view to extract starch from them, may answer for grinding horse-chestnuts.
He had a grater made of plate iron, in a cylindrical form (fig. 1.) about seven inches in diameter, and about eight inches high; the bars made by stamping the holes are on the inside. This grater is supported upon three feet AAA, made of flat iron bars, seven feet high, strongly riveted to the grater; the bottom of each foot is bent horizontally, and has a hole in which receives a screw, as at A, fig. 4. A little below the upper end of the three feet is fixed a cross piece B (fig. 1. and 4.), divided into three branches, and riveted to the feet. This cross piece not only serves to keep the feet at a proper distance from each other, and to prevent their bending; but the centre of it having a hole cut in it, serves to support an axis or spindle of iron, to be presently described.
The upper end of this cylindrical grater has a diverging border of iron C (fig. 1. 4. and 7.), about ten inches in diameter at the top, and five inches in height.
Within this cylindrical grater is placed a second grater (fig. 2. and 3.), in the form of a cone, the point of which is cut off. The latter is made of thick plate iron, and the bars of the holes are on the outside; it is fixed, with the broad end at the bottom, as in fig. 4. At the upper end of the cone is riveted a small triangle, or cross piece of iron, consisting of three branches D (fig. 2.), in the middle of which is made a square hole, to receive an axis or spindle; to give more resistance to this part of the cone, it is strengthened by means of a cap of iron E, which is fixed to the grater by means of rivets, and has also a square hole made in it, to let the axis pass through.
Fig. 3. represents the same cone seen in front; the base F has also a cross piece of three branches, riveted to a hoop of iron, which is fixed to the inner surface of the cone; the centre of this cross piece has also a square hole for the passage of the axis.
Fig. 5. is a spindle or axis itself; it is a square bar of iron about 16 inches long, and more than half an inch thick; round at the bottom, and also towards the top, where it fits into the cross piece I, fig. 7. and B, fig. 1. and 4.; in these pieces it turns round, and by them it is kept in its place. It must be square at its upper extremity, that it may have a handle, about nine inches long, fixed to it, by means of which the conical grater is turned round. At G, (fig. 5.), a small hole is made through the axis, to receive a pin H, by means of which the conical grater is kept at its proper height within the cylindrical one.
Fig. 6. is a bird's eye view, in which the mill is represented placed in an oval tub, like a bathing-tub. I is the fore-mentioned triangular iron cross, fixed with screws to the side of the tub; the centre of it has a round hole, for the axis of the mill to move in when it is used.
Fig. 7. represents the mill in the oval tub; it is placed at one end of it, that the other end may be left free for any operation to be performed in it which may be necessary. A part of the tub is cut off, that the inside of it, and the manner of fixing the mill, may be seen. That the bottom of the tub may not be worn by the ferrous which passes through the feet of the mill, a deal board, about an inch thick, and properly shaped, is placed under the mill.
When we wish to make use of this mill, it is to be fixed by the feet, in the manner already described; it is also fixed at the top, by means of the cross piece I, fig. 6. and 7. The tub is then to have water poured into it. into it as high as K, and the top of the mill is to be filled with potatoes, properly washed and cut; the handle L is to be turned round, and the potatoes, after being ground between the two graters, go out gradually at the lower part, being assisted by the motion produced in the water by the action of the mill.
It is not necessary, in the construction of such a mill, to be very particular with respect to its proportions; but, in order to make known those which experience has proved to be good ones, a scale is given with the figures, to which recourse may be had. With a mill of this size, 100 pounds of potatoes may be ground in the space of two hours.
We are persuaded that this mill will answer perfectly well for grinding horse chestnuts; and we hope, that where they can be had they will be used in preference to potatoes. We shall, however, give M. Baume's method of extracting starch from the ground potatoes, not only because it will be acceptable to those who have not horse-chestnuts, but also because those who have may, by following it, be able, perhaps, to make starch of them, without encroaching upon Lord William Murray's patent.
In order to prepare starch from potatoes, says M. Baume, any quantity of these roots may be taken, and soaked in a tub of water for about an hour; they are afterwards to have their fibres and shoots taken off, and then to be rubbed with a pretty strong brush, that the earth, which is apt to lodge in the inequalities of their surface, may be entirely removed; as this is done, they are to be washed, and thrown into another tub full of clean water. When the quantity which we mean to make use of has been thus treated, those which are too large are to be cut into pieces about the size of eggs, and thrown into the mill; that being already fixed in the oval tub, with the proper quantity of water; the handle is then turned round, and as the potatoes are grated they pass out at the bottom of the mill. The pulp which collects about the mill must be taken off from time to time with a wooden spoon, and put aside in water.
When all the potatoes are ground, the whole of the pulp is to be collected in a tub, and mixed up with a great quantity of clean water. At the same time, another tub, very clean, is to be prepared, on the brim of which are to be placed two wooden rails, to support a hair sieve, which must not be too fine. The pulp and water are to be thrown into the sieve; the flour passes through with the water, and fresh quantities of water are successively to be poured on the remaining pulp, till the water runs through as clear as it is poured in. In this way we are to proceed till all the potatoes that were ground are used.
The pulp is commonly thrown away as useless; but it should be boiled in water, and used as food for animals; for it is very nourishing, and is about 4ths of the whole quantity of potatoes used.
To return from this short digression. The liquor which has passed through the sieve is turbid, and of a brownish colour, on account of the extractive matter which is dissolved in it; it deposits, in the space of five or six hours, the flour which was suspended in it. When all the flour is settled to the bottom, the liquor is to be poured off and thrown away, being useless; a great quantity of very clean water is then to be poured upon the flour remaining at the bottom of the tub, which is to be stirred up in the water, that it may be washed, and the whole is to stand quiet till the day following. The flour will then be found to have settled at the bottom of the tub; the water is again to be poured off as useless, the flour washed in a fresh quantity of pure water, and the mixture passed through a silk sieve pretty fine, which will retain any small quantity of pulp which may have passed through the hair sieve. The whole must once more be suffered to stand quiet till the flour is entirely settled; if the water above it is perfectly clear and colourless, the flour has been sufficiently washed; but if the water has any sensible appearance either of colour or of taste, the flour must be again washed, as it is absolutely necessary that none of the extractive matter be suffered to remain.
When the flour is sufficiently washed, it may be taken out of the tub with a wooden spoon; it is to be placed upon wicker frames covered with paper, and dried, properly defended from dust. When it is thoroughly dry, it is to be passed through a silk sieve, that if any dotted lumps should have been formed they may be divided. It is to be kept in glass vessels stoppered with paper only. See Vegetable Substances, Suppl.
N.B. Almost all the flour of potatoes that is to be bought contains a small quantity of sand, which is perceived between the teeth; it is owing to the potatoes not having been properly washed; for the sand which lodges in the knobs and wrinkles of these roots, is not always easy to get out.
STIRLING'S, or STERLING'S, the name given to the strong pieces of timber which were driven into the bed of the river to protect the piles, on the top of which were laid the flat beams upon which were built the bases of the stone piers that support the arches of London bridge. In general, stirlings are large piles placed on the outside of the foundation of the piers of bridges, to break the force of the water, and to protect the stone work from injury by floating ice. They are otherwise called JETTES, which see in this Supplement; and their place is often supplied by large stones thrown at random round the piers of bridges, as may be seen at Stirling bridge when the river is low; and as was done by Mr Smeaton's direction round the piers of the centre arch of London bridge, when it was thought in danger of being undermined by the current. See Smeaton, Encycl.