SUBSTANCES PRODUCED BT PLANTS. 55 



and is termed Dextrin. In the vegetating barley, therefore, 

 there must exist some agent which is not to be found in the 

 unmalted grain and which is capable of effecting this impor- 

 tant transformation. It is a truly brilliant achievement for 

 modern science to have succeeded in investigating this curious 

 subject, and to have ascertained that the agent which pro- 

 duces the change is a peculiar substance named Diastase, rich 

 in nitrogen, and which you shall presently see performs an 

 important office in the first period of vegetable Hfe. 



But science, though it can trace and regulate the changes 

 produced by this curious agent, is unable to form it from its 

 elements, but can merely employ it as developed by nature 

 in the vegetating grain. A method, however, has been dis- 

 covered, which enables us to a certain extent to imitate its 

 effects ; and as the process is of very great interest and may 

 yet become of practical impoitance to these countries, I will 

 briefly describe it. 



67. If we place in a porcelain dish over a lamp some 

 water containing a few drops of vitriol, and when the water 

 boils add gradually to it a small quantity of starch previously 

 beaten into a paste with water, the starch, instead of becom- 

 ing a jelly, as when boiled with pure water (65), is rendered 

 liquid, and after a few minutes' boiling, a drop of the solution, 

 taken out and touched with the solution of iodine, no longer 

 displays the blue colour which is characteristic of starch, 

 but a wine-red tinge, such as that exhibited in the solution 

 of the gum produced by the action of malt. If we continue 

 the boiling a few minutes longer, the iodine will produce no 

 change in the liquid, and if we now take the dish fi*om the 

 lamp, and add to it some powdered chalk until the acid taste 

 of the solution be destroyed, and allow the mixture to settle 

 that the compound which the chalk and the acid forms (46) 

 may subside, the clear liquid will be found perfectly sweet, 

 and crystals of sugar may be procured from it by careful 

 evaporation. 



68. Starch also undergoes transformation fiom the action 

 of other agents: thus, when it is heated to a temperatun^ 

 somewhat higher than that at which water boils, as is prac* 

 tised in the preparation of what is called British gum, it is 

 converted into dextrin ; some sugar is also produced in the ope- 

 ration, and even the simple exposure of starch jelly to the air 

 for a long period has been found to produce tlie same changes. 



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