242 



THE POPULAR EDUCATOR. 



obtained from flour by making it into a paste with water, then 

 washing this, tied in a muslin bag, in a gentle stream of water ; 

 the starch is removed in suspension, and this is being carried 

 on so long as the water runs through the bag milky. Upon 

 opening the bag a grey, sticky, tenacious substance is found 

 adhering to it, which is mainly gluten. It evidently is a com- 

 pound of at least two substances, one of which is soluble in 

 hot alcohol, the other is not. Liebig regards this latter 

 substance as vegetable fibrine ; the former, which is deposited 

 from the alcohol as it cools, has been termed gluten. 



Starch (C 6 H 10 5 ) n ; or amylaceous matter, occurs in a large 

 proportion in seeds, roots, and stems of certain plants. It 

 appears in grains : those in wheat (Fig. 55) are i^th of an 

 inch in diameter ; those of arrowroot (Fig. 56), g^th ; while those 

 of rice are much smaller, and they are also angular (Fig. 

 57). As sold in the shops, it is either in a white glistening 

 powder, or in peculiar angular masses, which are easily 

 crushed ; it is insoluble in cold water. If the water contain 

 2 per cent, of alkali, the starch becomes converted into a 

 tenacious mass; or if the water be heated to 60 Cent., it 

 suddenly assumes a pasty condition, in which state it is used by 

 the laundress. Under the microscope the grains seem to be con- 

 structed in layers ; but it is possible that this appearance is 

 due to folds in the skin which encloses them. The point a 

 (Fig. 55) is called the hilum, and is supposed to be the point 

 of attachment of the grain to the cellular tissue of the plant. 

 Starch is readily prepared from potatoes, of which root it forms 

 rather more than 80 per cent, of the solid matter, by causing 

 them to be rasped ; the pulp is then washed on a sieve, and the 

 water, milky with the granules of the starch in suspension, is 

 received into vats, where the amylaceous matter subsides. 

 After several washings and strainings, it is finally dried. 



Rice starch is more difficult to procure, from the fact that it 

 is associated with 7 per cent, of gluten in the seed. This 

 gluten is dissolved by a weak alkaline solution, which leaves 

 the starch untouched. 



The presence of starch is easily determined by the action of 

 iodine, which, as has been already noticed, turns it blue. 



From what we have seen of the insolubility of starch, it 

 must be evident that this substance is unfitted for the food of 

 the young shoot which the germinating plant puts forth, as 

 all food, to enter the minute vessels of either the animal or 

 vegetable frame, must be in a state of solution, and yet, were 

 the starch soluble, the rain would wash away the contents 

 of the husk as soon as it burst. These difficulties are solved by 

 one of the most wonderful of arrangements 



Dextrine. When a solution of starch is boiled with a little 

 dilute sulphuric acid, it becomes thin and limpid, and does 

 not give the blue compound with iodine ; the starch has become 

 dextrine, a substance closely resembling gum, and is indeed 

 sold as British gum, in those useful bottles of " mucilage." 



If this boiling with dilute acid be continued for some time, a 

 further and still more remarkable change takes place the 

 dextrine becomes grape sugar, or glucose (C 6 H 1!( O 6 ,H a O). 



This very same result is produced in seeds by a minute 

 quantity of a ferment, diastase, which is probably albumen or 

 gluten in a particular stage of decomposition; one part of 

 diastase can convert 2,000 parts of starch into sugar. In the 

 germinating plant this conversion is not sudden, but gradual, 

 thus supplying the rootlet with proper aliment as it requires it. 



In brewing, this natural process is taken advantage of to 

 convert the starch of the barley into sugar, and this sugar as 

 will be explained in the next lesson suffers, by fermentation, 

 a further change, becoming alcohol, carbonic acid gas, and 

 water. The barley is " steeped" in water, and then spread out 

 on a floor; here it begins to germinate, and by continually 

 turning the bed with wooden shovels, this germination goes on 

 uniformly. The acrospire is watched, and as soon as it is 

 "bout half an inch long, and is going to bifurcate, the vitality of 

 the seed is destroyed by rapidly drying the grain, experience 

 having taught the maltster that at this point all the starch has 

 become sugar ; the malt is then mixed with water, and allowed 

 to ferment. 



The saline matters plants contain they obtain directly from 

 the soil in which they grow, and are those phosphates, etc., of 

 which the mineral structures of the body are composed. The 

 great use of artificial manure is to supply soil which is deficient 

 in such salts with those peculiarly required by the nature of the 



crop proposed to be raised. The decay of the large cities, such 

 as Nineveh and Babylon, has been ascribed to the fact that 

 the land in their neighbourhoods became exhausted of its phos- 

 phates, and in time refused to grow cereal crops. The means 

 of importation being very imperfect, the population gradually 

 decreased, or emigrated. We renew the exhausted soil by sup- 

 plying it with guano, bone-earth, phosphate of lime, and other 

 artificial manures. 



Those constituents of the plant which we have noticed, which 

 are not of a mineral character, are assimilated by the plant 

 from carbonic acid gas, nitrogen, water, and oxygen. The 

 process by which these changes are effected is wholly unknown. 

 The green colouring matter of the leaf has the property, in 

 sunlight, of decomposing the carbonic acid which the leaves 

 the lungs of the plant inhale. The oxygen is thrown off in 

 a pure state, fit for animal respiration, while the carbon is re- 

 tained. Some of it forms the woody tissues of the plant ; some 

 of it, with the elements of water, and occasionally a little 

 nitrogen, concurs to produce gluten, starch, sugar, and the 

 other organic constituents of plants. 



Cellulin or Cellulose (C 18 H 30 O 15 ). This substance is the " base- 

 ment tissue " of all vegetable structures ; it occurs nearly pure 

 as cotton, linen, elder pith. The particles of woody matter are 

 deposited in the meshes of this cellulin. 



Pyroxyline, or Gun Cotton (C, 8 H al .9NO a ,0 ls ). When cellulin 

 is immersed in a mixture of equal measures of strong nitric acid, 

 whose specific gravity is 1'5, and sulphuric acid, it undergoes a 

 remarkable change. As may be seen by the above formula, 

 one of the oxides of nitrogen is introduced into its composition. 

 Apparently the fibre is not changed, but it has assumed the 

 property of rapid combustion. 



To prepare Gun Cotton. The mixed acids are allowed to cool to 

 the ordinary temperature of the air ; the cotton, paper, or sawdust, 

 is then immersed for some minutes ; the material must not be 

 immersed in large quantities, but piecemeal the paper, sheet 

 after sheet. After ten minutes it is removed, and thoroughly 

 drained from the acid, by pressing it between two porcelain 

 plates in an inclined position. It is now washed in cold 

 water, until not a trace of acid is left, and dried with care, at a 

 temperature not above 100 Cent. The rapidity of its explosion 

 may be shown by igniting a little gun-cotton resting on gun- 

 powder the latter is generally not fired. Although this 

 property renders it peculiarly adapted for blasting brittle rock, 

 yet for military purposes an explosive is required of slower 

 combustion, in order to heave the shot. Gun-cotton exerts its 

 propulsive force but for a short time, and distresses the 

 ordnance. This difficulty is now being overcome by com- 

 pressing the fibre, which renders the inflammation slower. It 

 possesses great advantages over gunpowder; it can be kept 

 without injury any length of time damp, and speedily dried for 

 use ; it leaves no " train " when carried about ; it is light, and, 

 above all, yields no smoke upon explosion. It will explode 

 when violently struck. When dissolved in ether, it forms the 

 collodion of the photographer. 



Lignine is the encrusting matter in the cellular tissue which 

 gives hardness to wood. 



