STARCH. 



417 



III. 



INDIFFERENT SUBSTANCES. 



There are a great number of so-called "indifferent" substances to which 

 \ve cannot be indifferent. Such bodies as these have neither acid nor basic 

 properties, and stand no comparison with salts. They are of great import- 

 ance, forming, as they do, the principal nutriment of animals. Some contain 

 nitrogen, some do not ; they may therefore be divided into nitrogenous and 

 non-nitrogenous substances ; the former for solid portions of the body, the 

 latter for warmth. 



We will take the latter first, and speak of some of them such as 

 starch, gum, sugar, etc. 



STARCH is found in the roots 

 of grain, in the potato, dahlia, arti- 

 choke, etc., and by crushing the 

 parts of the plant, and washing 

 them, the starch can be collected as 

 a sediment. In cold water and in 

 spirits of wine starch is insoluble. 

 The various kinds of starch usually 

 take their names from the plants 

 whence they come. Arrowroot is 

 obtained from the West Indian plant 

 Maranta A rundinacea. Cassava and 

 tapioca are from the manioc ; sago, 

 from the sago palm ; wheat starch, 

 and potato starch are other examples. 



If starch be baked in an oven 

 at a temperature of about 300 

 it becomes, to a great extent, 

 soluble in cold water, forming what is called "British gum"; this is 

 largely used for calico printing and other purposes ; if boiled in water 

 under great pressure, so that the temperature can be raised to the same 

 degree, it is also changed into an adhesive sort of gum, " mucilage " ; 

 this is the substance made use of by the government officials to spread 

 over the backs of postage and receipt stamps to make them adhere. 

 The starch of grain, during germination, or growth, contains diastase, which 

 converts the starch into gum and sugar ; the same effect can be produced 

 by heating starch with diluted sulphuric acid. 



GUM found in plants is chiefly procured from the Mimosa trees, from 

 which it flows in drops, and is called Gum Arabic. There are other 

 so-called " gums," but this is the one generally referred to. 



27 



ig. 428. Plantation ot sugar-canes. 



