grouped in rosettes. The crystals contain two molecules of water of crystallisation. It has a sweet taste, is soluble in water, but not in absolute alcohol, or ether.

It is precipitated by a mixture of basic lead acetate and ammonia. It is capable of the lactic acid fermentation' but not of the alcoholic. Its solutions have no action on polarised light; it does not reduce metallic oxides; it gives no change of colour when boiled with caustic potash, neither is it decomposed by weak acids.

Tests. (1) Evaporate a little of its solution with a little nitric acid on a platinum dish; treat the residue with a little ammonia and calcium chloride, and evaporate to dryness at a gentle heat. A bright red or violet colour is produced. This test only succeeds with pure solutions (Scherer).2

FIG. 42.-Inosite crystals.

(2) Add a little mercuric nitrate to a solution of inosite, on a porcelain dish; a yellow precipitate is produced. On heating this gently, it will become red; on cooling the colour vanishes. Proteids, tyrosine, and sugar must be absent (Gallois).

3

CHOH

CHOH

CHOH

Constitution. From a study of its nitro-substitution and other products, Maquenne concludes that the graphic formula for inosite may be thus represented. It is in other words a hexatomic alcohol with six secondary alcohol groups arranged in a ring; this symmetrical construction excluding any power to rotate polarised light according to the theory of Le Bel and Van 't Hoff (see p. 45). It is not an aldehyde, nor an acetone, nor a polyphenol, though the closed chain suggests an aromatic structure.

CHOH

CHOH

CHOH

CANE SUGAR

This sugar is generally distributed throughout the vegetable kingdom in the juices of plants and fruits, especially the sugar cane, beetroot, mallow, and sugar maple. It is a substance of great importance

1 According to Hilger (Ann. Chem. Pharm. vol. clx. p. 333) the variety of acid formed is sarcolactic.

2 Ann. Chem. Pharm. vol. lxxiii. p. 322.

3 Compt. rend. civ. (1887), 225, 297, 1719, 1853.

as a food; after abundant ingestion of cane sugar, traces may be found in the blood and urine, but the greater part undergoes inversion.

Pure cane sugar holds cupric hydrate in solution in an alkaline liquid, i.e. with Trommer's test it gives a blue solution. But no reduction occurs on boiling. It crystallises in monoclinic prisms. Aqueous solutions are dextrorotatory. (a)=+73.8°. By boiling with water, or more readily by boiling with dilute mineral acids, or by means of inverting ferments, it undergoes inversion, i.e. it takes up water and splits into dextrose and levulose.

C12H22O11+H2O=C6H12O6+C6H12O6

With yeast, cane sugar is first inverted by means of a special soluble ferment produced by the yeast cell, and then there is an alcoholic fermentation of the glucoses so formed. Nitric acid oxidises cane sugar to saccharic acid.

Cane sugar may be estimated in the following way :-Take 40 c.c. of the solution of cane sugar; add 1 c.c. of a 25 per cent. solution of sulphuric acid, and boil for half-an-hour. Care must be taken not to char the sugar. Bring the solution of sugar to its original volume by adding water. Place it in the burette, and run it into boiling Fehling's solution, as in the estimation of dextrose. It may be necessary to add excess of soda or potash to the Fehling's solution, so that the sulphuric acid in the sugar solution may be fully neutralised. Every 95 parts of glucose found corresponds to 100 parts of cane sugar.

LACTOSE

Lactose or milk sugar occurs in milk. It has also been described as occurring in the urine of women in the early days of lactation or after weaning.

It crystallises in rhombic prisms, which contain a molecule of water of crystallisation. It is soluble in six parts of cold, and 2 parts of hot, water. It is thus much less soluble than cane sugar or dextrose. It has only a faint sweet taste. Aqueous solutions are dextrorotatory. (a)=+59·3°. FIG. 43.-Milk sugar crystals. It is insoluble in alcohol and in ether. Solutions of lactose reduce Fehling's solution, but less powerfully than dextrose. If it required seven parts of a solution of dextrose to

ᄆ

1 Most specimens of commercial cane sugar contain other forms of sugar as impurities, and these cause a small amount of reduction.

reduce a given quantity of Fehling's solution, it would require ten parts of a solution of lactose of the same strength to reduce the same quantity of Fehling's solution.

By boiling with water, or more readily by boiling with dilute acids, or by means of inverting ferments, as in the alimentary canal, it takes up water and is converted into a glucose called galactose:

With yeast, lactose is first inverted to galactose, and with this the alcoholic fermentation takes place; but this occurs slowly. With the lactic acid organism, that which brings about the souring of milk, the lactic acid fermentation is produced; this may also occur as the result of the action of putrefactive bacteria, e.g. in the alimentary canal. The lactic acid fermentation consists of the two stages represented by the following equations :---

Nitric acid oxidises lactose to mucic acid.

To detect lactose in milk.—Acidulate slightly with acetic acid, boil, filter, and test the filtrate with Fehling's solution, or by Böttger's bismuth test.

Το prepare lactose from milk.-Acidulate with acetic acid to precipitate the casein and fat; filter; boil again to precipitate albumin and filter again; evaporate the filtrate to a small bulk; set aside to crystallise; the crystals may be purified by recrystallisation.

MALTOSE

Maltose is the end product of the action of malt-diastase on starch, and can also be formed as an intermediate product in the action of dilute sulphuric acid on the same substance. It also appears to be the

chief

sugar formed from starch by the diastatic ferments contained in the saliva (ptyalin) and pancreatic juice (amylopsin).

Maltose can be obtained in the form of acicular crystals; aqueous solutions are strongly dextrorotatory. (a) +150°. Solutions of maltose reduce alkaline solutions of copper, bismuth and other metallic salts; but its reducing power as measured by Fehling's solution is one third less than that of dextrose.

By prolonged boiling with water, or more readily by boiling with a

dilute mineral acid, or by means of an inverting ferment, such as occurs in the intestinal juice, it is converted into dextrose.

Starch is widely diffused through all parts of the vegetable world. It occurs in nature in the form of microscopic granules; these vary in appearance and size according to their source, but each consists of a central spot around which are more or less parallel rings of starch proper or granulose, alternating with layers of cellulose. A variety of granulose is present in small amount, which gives a red colour with iodine; it is called erythro-granulose (Brücke).

It is nearly insoluble in cold water. When boiled with water, the granules burst, and an imperfect opalescent solution is formed. If concentrated, this gelatinises on cooling. It is also insoluble in alcohol and in ether. It is a colloid substance; that is, it does not pass through animal membranes, or vegetable parchment.

Tests. (1) With iodine it gives a blue colour, which disappears on heating, the iodide of starch being dissociated at a high temperature: on cooling it reappears. In performing this test, care must be taken not to apply heat for too long a time, or all the iodine is driven off and consequently no blue colour reappears on cooling.

(2) Tannic acid gives a yellow precipitate, which dissolves on heating.

(3) Solutions of starch are dextrorotatory. (a)=+216°.

Decompositions. At 200° C. dry starch, at 160° C. solutions of starch, are changed into dextrin. Prolonged heating changes it into dextrose. It is rapidly converted into dextrose by heating it with dilute mineral acids. It may in this way be estimated quantitatively, 90 parts of the dextrose so formed corresponding to 100 parts of starch. By the action of diastatic ferments,' maltose is, as we have seen, the chief end product; here also dextrin is an intermediate stage. When starch is converted into dextrose by the action of acids, the following equation represents what occurs :

3C6H1005+ H2O = C6H12O6 + C6H10O5 + C6H10O5

[star:h]

[dextrose] [achroo-dextrin] [erythro-dextrin]

1 Raw starch is less readily acted on by ferments than boiled starch, and the starches from different plants vary much in digestibility.

If some starch solution be boiled with dilute mineral acids, or be acted on by diastatic ferments, the solution will become clear from the formation of a polymeride of starch, called soluble starch or amidulin; this like the original solution gives a blue colour with iodine; as the action progresses the blue colour becomes less and less intense, then mixed with a red tint to form violet, and then replaced by the red tint due to the presence of a form of dextrin called erythrodextrin. If the liquid be tested with Fehling's solution, reduction will show the presence of dextrose or maltose. Dextrin and sugar are produced simultaneously (see above equation). Testing the liquid a little later, the reduction with Fehling will be found much more abundant, and testing with iodine there will be no colouration : this is due to the conversion

of erythro-dextrin into sugar. If alcohol be added, a precipitate is produced; this consists of a form of dextrin which gives no colour with iodine, and which is consequently called achroo-dextrin. It is converted ultimately into sugar also, but with greater difficulty than is erythro-dextrin.

The formation of maltose from starch may be represented by the following equation (Brown and Morris) :

10(C6H1005)+4„H2O=4„C12H22O11+ (C12H20010)

Dextrin is the name given to the intermediate products in the hydration of starch, and Brücke distinguishes two varieties: erythrodextrin, which gives a red-brown colour with iodine, and achroo-dextrin, which does not. It is said to occur in small quantities in blood, muscle, and liver; also occasionally in diabetic urine (Reichardt).'

Dextrin is readily soluble in water, but insoluble in alcohol and ether. It is gummy and amorphous. It does not reduce Fehling's solution, nor does it ferment with yeast. It has a strong dextrorotatory action. (a)+138-88°. By hydrating agencies it is converted into glucose.

Dextrin gives the same, or a very similar, colour with iodine as glycogen does. It may be distinguished from glycogen by the want of opalescence of its solutions, and by its not being precipitable by basic acetate of lead. It is, however, precipitable by basic acetate of lead and ammonia.

Dextrin gives also a very similar colour to that given by erythrogranulose. That dextrin and erythro-granulose are not identical is shown by their having a different affinity for iodine. If a small

1 Reichardt, Zeit. Anal. Chem. 1875.