STAR-FORT, a kind of redout inclosing an area, and having its lines of rampart or parapet disposed, on the plan, in directions making with each other angles which are alternately salient and re-entering, as a star is usually represented. This construction is adopted when the work is intended to contain, for some time, the stores of an army, or to secure some important part of the position which the army occupies. The magistral line of the work may be traced by first laying down a polygonal figure, regular or irregular, as the ground may permit, and then upon each of its sides forming an equilateral triangle : the interior capacity and the quantity of fire will evidently be increased as the polygon has a greater number of sides; but the importance of the work is seldom so great as to render it necessary to form it on a polygon superior to a hexagon or sn octagon ; and the latter polygon, while it admits of being easily traced, allows the re-entering angles between the sides of the triangles to have a degree of obtuseness sufficient to avoid the risk that the defenders of the faces on each side of such an angle might fire upon one another. As it is found that soldiers fire nearly perpendicularly to the face of the parapet behind which they stand, a greater obtuseness would cause the lines of fire to diverge so far from the direction of the adjacent face as to prevent the ditch of the latter from being effectually flanked.
A star-fort on an octagon may, if the ground is level, be traced by laying down a square, and, upon the middle of each of its sides, an equilateral triangle, whose base is one-third of the length of such side ; or, more regularly, by transferring half the diagonal of the square to each side, from the four angles ; the distances between the extremities of these half diagonals are the sides of an equilateral octagon, and upon these sides equilateral triangles may be formed. The subjoined cut represents the magistral line of half a star-fort with eight points, con structed in this last manner. If the polygon had more than twelve
sides, the re-entering angles would be acute ; and, agreeably to the above supposition concerning the direction in which soldiers fire, the defenders on the adjacent faces might annoy one another.
That the fire of musketry may be sufficiently effective, it is con sidered proper that the lengths of the several faces should not be less than thirty yards ; and a star-fort whose faces are of much greater position of the hilum, are always the same in any one kind of starch, but vary considerably in starch from various sources ; the microscope is therefore of considerable aid in detecting the admixture of au inferior with a superior variety, and in determining the origin of a starch.
Starch is insoluble in, and but very slightly acted upon by, cold water ; nor is it really soluble in hot water. When, however, it is heated with twenty or thirty times its weight of water its granules swell and finally burst; if the whole be diluted and set aside, the rent walls of the granules subside to the bottom of the containing vessel, while their contents are so thoroughly mixed with the water that the two can only be separated by very tedious processes. Starch is also insoluble in alcohol or ether. Acids and alkalies, even when cold and highly diluted, cause it to swell and form a paste and finally convert it into dextrin. Air-dried starch usually contains about eighteen per cent. of water ; if more than this is present the starch has a tendency to agglutinate when pressed between the finger and thumb ; moreover, when projected on to a metal plate heated to 212° Fahr., it agglo merates into hard lumps forming a sort of artificial tapioca, no such effect being produced if it has been properly air-dried. Exposed in vacuo at a temperature of 60° Fahr., the amount of water is reduced to fifteen per cent. and at 260° Fahr. to the minimum of eight and a half per cent. At a higher heat than this, starch is converted into dextrin.