114 SUGARS AND SOME ALLIED BODIES. VARIETY AND ORIGIN OF SUGAR. PRINCIPAL PROPERTIES. Crystallizes in four-sided prisms-is less soluble in water than grape sugar--is nearly insoluble in alcohol and ether-is precipitated from its solutions by ammoniacal acetate of lead-reduces the salts of copper, silver, and mercury, when its alkaline solution is boiled with them-produces right-handed rotation=56°4—is not directly susceptible of alcoholic fermentation-is converted into galactose by boiling with dilute acids-yields mucic and oxalic acids with nitric acid. Crystallizes in brilliant rectangular octohedra or in rhombic prisms-produces right-handed rotation = 220°-if heated quickly it fuses at 212, and at 266° (130° C.) loses H., and becomes solid-may be heated without decomposition to 410° (210° C.), when it melts again-loses its water of crystallization-is very soluble in water, and in hot alcohol-is sparingly soluble in cold alcohol and ether-is precipitated by ammoniacal acetate of leaddoes not reduce potassio-cupric tartrate - ferments slowly and imperfectly with yeast-yields dextrose when heated with dilute acids-does not give mucic with nitric acid, but when heated with it yields saccharic and oxalic acids. Crystallizes in short, hard, efflorescent rhombic prisms-is very soluble in water-sparingly soluble in alcohol, either hot or cold-insoluble in ether-has a sweetness about that of glucosefuses at 280° (138° C.)—is precipitated by ammoniacal acetate of lead-does not reduce the alkaline potassio-cupric tartrate-produces right-handed rotation=94°1-ferments with difficulty-yields dextrose when heated with dilute acids-gives no mucic acid with nitric acid. Crystallizes in slender prisms-is freely soluble in waterMelitose, slightly soluble in alcohol-is feebly sweet-melts and loses water at 260° (127°C.)-yields a precipitate with ammoniacal acetate of lead 12H2412, 2 H2;does not reduce an alkaline solution of potassio-cupric tartrate (Berthelot) from the Eucalyptus. exerts right-handed rotation=102°-undergoes alcoholic fermentation with yeast, at the same time half the sugar is separated in an unfermentable form as eucalin-furnishes mucic acid with nitric acid-is little affected by alkalies. Is not crystallizable-precipitates ammoniacal acetate of lead, and reduces the alkaline potassio-cupric tartrate when boiled with it-produces right-handed rotation = about 50°-is not susceptible of alcoholic fermentation with yeast-becomes brown when treated with alkalies-is not altered by boiling with dilute acids. Crystallizes in octohedra with a rectangular base-is very soluble in water-nearly insoluble in alcohol-sp. gr. 165-is fusible without loss of weight-gives a white precipitate with ammoniacal acetate of lead-reduces the alkaline solution of potassio-cupric tartrate on heating it with it-occasions left-handed rotation=-46°*9 -is not fermentable with yeast, but with cheese and chalk slowly yields lactic and butyric acids and alcohol-becomes brown when treated with alkalies-yields a red solution with oil of vitriol—is converted into oxalic and a little racemic acid by nitric acid. Crystallizes in radiated tufts-is soluble in water-insoluble in absolute alcohol and ether-loses water by heat, and fuses at +10° (210° C.)-has no rotatory power on polarized light-does not reduce the alkaline potassio-cupric tartrate when boiled with it—is not susceptible of alcoholic fermentation, but with cheese and chalk yields lactic and butyric acids-is not altered by boiling with dilute acids or alkalies-forms a precipitate with ammoniacal acetate of lead. SUGARS AND SOME ALLIED BODIES. 115 VARIETY AND ORIGIN OF SUGAR. PRINCIPAL PROPERTIES. Crystallizes in silky anhydrous four-sided prisms-is soluble in water and alcohol-fuses at 320° (160° C.)—gives a precipitate with ammoniacal acetate of lead-reduces the salts of silver or gold by heat-does not reduce the alkaline potassio-cupric tartrate when boiled with it-exerts no rotatory power on polarized light-is not easily fermentable-with nitric acid yields saccharic and oxalic acids-is soluble without coloration in oil of vitriol, and in alkaline solutions. Crystallizes in broad voluminous crystals of the pyramidal system -is soluble in water and in alcohol-fuses at 248° (120° C.)-has no rotatory power-gives no precipitate with ammoniacal acetate of lead-does not reduce the alkaline potassio-cupric tartrate-yields no mucic acid with nitric acid-is not fermentable. Crystallizes in brilliant prisms-is soluble in water and in alcohol -fuses at 356° (180° C.)—gives no precipitate with acetate or with subacetate of lead-does not reduce nitrate of silver or chloride of gold-produces no rotation on polarized light-is not susceptible of fermentation with yeast-is not affected by dilute alkalies-is converted into mucic acid by nitric acid. Crystallizes in transparent prisms-is soluble in water and dilute alcohol-is fusible at 420° (215°5 C.)-does not reduce the alkaline potassio-cupric tartrate-is not fermentable by yeast- is soluble without change of colour in oil of vitriol and in the alkalies -yields oxalic acid with nitric acid. Crystallizes slowly in hard hemispherical radiated masses-has a very sweet taste-is very soluble in water-is sparingly soluble in alcohol-gives a precipitate with ammoniacal acetate of leaddoes not reduce the alkaline potassio-cupric tartrate-sp. gr. 1'52 -produces right-handed rotation-is not fermentable-fuses below 480° (249° C.)-does not yield mucic with nitric acid. § II. VARIETIES OF STARCH AND Gum. (1092) STARCH Ꮎ (ЄH100).—The term starch, or amylaceous matter, or fecula, is applied to an organized substance which occurs in rounded or oval grains in the cellular tissue of certain parts of plants. It is met with in great abundance in all dicotyledonous seeds, particularly in those of leguminous plants, such as peas and beans. The monocotyledonous seeds of the Cerealia or corn tribe contain it still more largely; it is also abundant in the tubers of the potato, in the roots of the tapioca and arrowroot, and in a variety of other plants. On examining the grains. of starch with a magnifying power of 300 or 400 diameters, they are seen to consist of flattened ovate granules, which in the same plant are tolerably uniform in size, but which vary in magnitude in different species of plants; those of the canna, or tous les mois, No. 1, fig. 382, being about of an inch (o'1 millimetre) in diameter; those of the potato are somewhat smaller, but the grains become larger as the age of the plant increases; those of the arrow-root, No. 2, do not exceed of an inch; those of FIG. 382. wheat starch, No. 3, are more circular, and about of an inch (0.025 millimetres) in diameter, and do not exhibit rings; those of rice, No. 4, are angular and often adherent to each other; they do not usually exceed the 3 of an inch, whilst those contained in the cells of the beet-root are still smaller. Each of the larger grains exhibits a series of concentric rings; some observers consider this appearance to indicate that they have been formed by a deposition of successive layers of starchy matter within an external envelope; Busk believes that the rings are occasioned by a plication of the envelope itself: in many instances the hilum, or supposed point of attachment of the grain to the cellular tissue of the plant from which it was developed, is distinctly perceptible, as shown at a, a, fig. 382. The structure of the grains of starch is very beautifully displayed by placing some of them in contact with a drop of concentrated solution of chloride of zinc (tinged with a little free iodine), on the field of the microscope. No change takes place in the granules until a little water is added. They then become of a deep blue colour, and gradually expand; at first a frill-like plicated margin is developed around the globule; by degrees this opens out; the plications upon the globule may then be seen slowly unfolding, and may be traced in many cases into the ruga of the frill; ultimately the granules swell up to 20 or 30 times their original bulk, and present the appearance of a flaccid sac. During these changes no extrusion of anything within the STRUCTURE AND PROPERTIES OF STARCH. 117 granules is observed to take place (Busk, Quart. Jour. Microscop. Soc., vol. i.). The grains of potato starch, if illuminated by polarized light, with a Nicol's prism interposed between the object and the eye, present a well-marked black cross, the centre of which corresponds with the hilum. When wheat starch is subjected to a similar test this cross is not perceptible; its presence may therefore be of service as a means of distinguishing the fraudulent addition of potato starch or flour to wheat flour. If (1093) Properties.-As sold in the shops, starch exhibits the appearance of a white glistening powder, or of columnar masses which are easily reduced to powder; when pressed between the fingers it emits a peculiar sound, and produces a certain feeling of elasticity. Starch is heavier than water, having a sp. gr. of about 15. It is insoluble in cold water, alcohol, and ether. placed in a solution of soda or of potash which contains 2 per cent. or upwards of alkali, the granules of starch swell up and become converted into a tenacious paste. A mixture of starch and water may be preserved without alteration at ordinary temperatures for an indefinite period; but it undergoes a remarkable change when heated to a temperature a little above 140° (60° C.) Under these circumstances the exterior layer of the granules absorbs water, the grains swell up, and the mixture suddenly assumes a viscous, pasty condition, in which form it is extensively employed by laundresses for stiffening linen. If this paste be largely diluted with water, the swollen granules of the starch slowly subside, whilst a certain quantity of amylaceous matter remains in solution. The starch paste thus obtained does not, when evaporated, recover its former insolubility. Its solutions are precipitated by alcohol, and the precipitate may be redissolved by the immediate addition of water; but after a few hours the flocculi become more coherent and are no longer soluble in cold water. A solution of starch produces right-handed rotation of a polarized ray. The soluble portion of starch is often termed amidin, from the French amidon, starch. Soluble starch, free from dextrin, is readily obtained by boiling the grains of starch with a strong solution of chloride of zinc, or with glacial acetic acid. Prolonged boiling with water alone has a similar effect, but dextrin is gradually formed (Maschke). It is remarkable, that if starch be boiled under pressure, at about 302° (150° C.), with from 5 to 15 times its weight of water, a thin solution is obtained, which may be filtered from the insoluble portion; this liquid, as it cools, deposits minute spherical 118 PROPERTIES OF STARCH. granules, which, when dried, have the whiteness of starch without its glistening appearance. These granules are sparingly soluble in cold water, but are readily dissolved when the water is raised to 158° (70° C.) or upwards. Iodine tinges them blue, and alcohol causes a precipitate when added to their aqueous solution. Starch, in the form in which it is usually sold, contains about 18 per cent. of water; in order to render it anhydrous, it should be dried in vacuo, at a temperature of 260° (127° C.) When dry starch is heated sufficiently, it becomes soluble in cold water, and forms a ropy solution much resembling gum in properties. The grains of anhydrous starch may be heated to 320° (160° C.) without becoming soluble, but at 400° (204° C.) the change is complete in the course of an hour or two. Commercial starch, on the contrary, from the water which it retains, is rendered completely soluble by raising the temperature suddenly to 320°, and maintaining it at this point for some time. The change produced in these cases consists in the formation of a substance isomeric with starch, which is termed dextrin (1099). soluble torrefied starch is known under the name of British gum, and constitutes the leiogomme of the French manufacturers; it is largely employed by calico printers for mixing with their colours, in order to give them the requisite consistence. When starch is subjected to dry distillation, acetic acid and marsh gas are among the products. This Like most organized structures, starch appears to retain as an essential component a small quantity of saline matter, consisting partly of potash; and it likewise contains a perceptible amount of some azotised compound, which is present chiefly in the tegument of the grains (Jacquelain). A solution of tannic acid occasions a precipitate in one of starch. When a dilute solution of starch is mixed with one of the ammoniacal acetate of lead, an insoluble compound with oxide of lead (Є12H189,2PbO) is formed. Starch may be recognised when present by the deep blue colour which it acquires on the addition of free iodine to its solution; this colour disappears if the solution be heated, but it re-appears as the liquid cools (394). If boiled with diluted sulphuric acid, starch quickly loses its viscidity, and is ultimately converted into dextrose. Before the transformation is complete, it passes through the same modification that exists in British gum, which has received the name of dextrin, from its property of causing the rotation of a polarized ray from left to right. During germination, the diastase of the seed converts the starch into a soluble mixture, |