CHAMBERS'S INFORMATION FOR THE PEOPLE. 



to crystallise out. The formula of cane-sugar and 

 milk-sugar is C^H^O^ When cane-sugar is 

 boiled with dilute acids, or mixed with water and 

 * diastase ' (a peculiar substance contained in malt), 

 it takes up water, and is converted into dextrose 

 and levulose, two sugars of the first, or grape- 

 sugar, set: C 12 H 22 O 11 +H 2 O = C 6 H 12 O 6 -fC 6 H 12 O 6 . 

 Milk-sugar undergoes a similar change. 



The two sets of sugar are chiefly distinguished 

 from one another by the readiness with which 

 they undergo chemical change, the second set 

 being the more stable. Thus, in fermentation, 

 cane and milk sugars are first changed into sugars 

 of the grape-sugar set, and then these ferment. 

 Cane-sugar can be obtained in crystals, as in loaf- 

 sugar and sugar-candy ; when heated, it fuses, 

 and on cooling, forms a clear, glassy, non-crystal- 

 line mass, ' barley-sugar,' which, if long kept, goes 

 back into the crystalline form. More strongly 

 heated, it loses water, and is converted into a 

 dark-brown substance, called caramel, which is 

 largely used for colouring rum and brandy. 



2. Starch occurs in many parts of plants, as in 

 the seeds of cereal grains, in the tubers of the 

 potato, in the stems of the sago-palm, &c. When 

 starch is examined under the microscope, it is 

 seen to consist of small rounded granules ; these 

 granules vary considerably in size and shape in 

 different plants, so that it is possible, by means 

 of the microscope, to discover the source from 

 which a specimen of starch was derived. Starch 

 is insoluble in cold water ; when treated with hot 

 water, the granules swell up, and form a paste, 

 which, when diluted, has all the appearance of 

 a solution. Starch-paste is coloured blue by 

 iodine, and may thus be used as a test for free 

 iodine ; similarly, iodine is used as a test for 

 starch. W T hen starch is heated alone, or with a 

 small quantity of acid, it is converted into dextrine, 

 a soluble gummy substance, much used in the 

 arts under the name of British gum. Prolonged 

 boiling with dilute acids, and also contact with 

 some animal liquids, convert starch into dextrose, a 

 sugar of the grape-sugar set. The same change 

 takes place in the starch contained in seeds during 

 the process of germination. Thus, malt, which 

 is grain in which the process of germination has 

 been arrested, contains, not starch, but dextrine 

 and dextrose derived from starch. Malt also 

 contains a remarkable substance called ' diastase/ 

 which converts starch into dextrine and dextrose. 



Inulin resembles starch very much ; it occurs in 

 the Jerusalem artichoke, the roots of the dahlia, 

 chicory, &c. It dissolves in hot water, and does 

 not form a jelly like starch. By boiling with dilute 

 acids it is converted into levulose, a sugar of the 

 grape-sugar set Starch, inulin, and dextrine 

 have all the same composition (C 6 H 10 O 5 ). 



Gum-arabic is a compound of a base or bases, 

 generally lime, magnesia, and potash, with Arabic 

 acid (C 6 H 10 O 5 ). Gum-senegal, cherry-tree gum, 

 gum-tragacanth, all of which are exudations from 

 trees, have a similar composition. 



3. The last carbohydrate of which we shall treat 

 is cellulose. This substance has the same com- 

 position as starch, inulin, dextrine, and Arabic 

 acid namely, C 6 H 10 O 5 . It occurs in all plants, 

 nearly pure in cotton, wool, and young fibrous cells, 

 such as flax, hemp, &c. ; and more or less mixed 

 with resinous and other matters in wood. It is 

 quite insoluble in water. When treated with 



332 



strong sulphuric acid, it is converted into a jelly, 

 which dries up to a horny mass. If unsized 

 paper, which is almost pure cellulose, is dipped 

 for a few minutes in sulphuric acid diluted with 

 about half its volume of water, then washed and 

 dried, a substance called ' vegetable parchment ' 

 is formed, which consists of the fibres of the paper 

 matted together by means of the above-mentioned 

 horny substance. If the jelly is boiled with dilute 

 acid, it is slowly converted into a sugar of the 

 grape-sugar set. Strong nitric acid converts 

 cellulose into gun-cotton. There are several kinds 

 of gun-cotton, the most explosive having the 

 composition C 6 H 7 (NO 2 ) 3 O 5 . 



FERMENTATION. 



If a solution of sugar containing nitrogenous 

 matter is exposed to the air at temperatures 

 between 75 and 95 F. what is called fermenta- 

 tion takes place. There are several kinds of 

 fermentation to which sugar is liable : we shall 

 here consider only two namely, the vinous or 

 alcoholic, and the lactic. Each kind of fermenta- 

 tion is produced by the growth in the liquid of a 

 special kind of mould or small fungus, which is 

 called a 'ferment;' and fermentation can be pre- 

 vented by anything which prevents the growth of 

 the fungus : for instance, by keeping away from 

 the liquid the spores or germs from which the 

 fungus springs ; by the liquid being either too hot 

 or too cold ; by its containing too much sugar ; 

 or by the presence of substances which act as 

 poisons to the ferment, and are hence called 

 ' antiseptics.' The fungus or ferment which pro- 

 duces the alcoholic fermentation is called ' yeast ;' 

 that which produces the lactic fermentation is 

 probably the mould called Penicillium glaucum, 

 the common ' blue mould.' The vinous fermenta- 

 tion proceeds most favourably between 75 and 85 

 F. ; the lactic, between 85 and 95. In the vinous 

 fermentation, the sugar is changed into alcohol 

 and carbonic acid gas, the latter escaping in 

 bubbles from the surface, and giving rise to an 

 appearance of frothing, whence the name ' fermen- 

 tation.' Some other substances, ' secondary pro- 

 ducts of fermentation,' are produced at the same 

 time in small quantity. The chief chemical 

 change may be represented by the equation, 



C 6 H 12 6 



Glucose. 



2C 2 H 6 O 



AlcohoL 



2CO 2 . 

 Carbonic Acid. 



In the lactic fermentation, the sugar is changed 

 into lactic acid thus : 



C 6 Hj 2 O 6 = 2C 3 H 6 O 3 . 



Glucose. Lactic Acid. 



The alcoholic fermentation occurs in the making 

 of bread. See CHEMISTRY APPLIED TO THE ARTS. 

 Alcohol is obtained from fermented liquors by 

 distillation (see p. 306). Pure alcohol is a col- 

 ourless liquid, of specific gravity 0-794, boiling 

 at 173 F. Its composition is indicated by the 

 formula C 2 H 6 O. It is inflammable, burning with 

 a feebly luminous flame, and producing carbonic 

 acid and water. It is capable of dissolving many 

 substances, and is used as a solvent for resins : 

 an alcoholic solution of shellac is the common 

 4 spirit varnish.' 



Alcohol acts upon acids in a manner very similar 

 to that of bases. Thus, with hydrochloric acid, 



