? REPARATION AND DECOMPOSITION OF STARCH. 10''' 



3°. When the raw potato is peeled and grated on a fine grater, aiid 

 the pulp thus produced well washed with water, potato starch is ob- 

 tained in the form of a fine white powder, consisting of rounded, glossy 

 and shining particles. 



4°. When the roots of the Maranta Arundinacea of the West India 

 Islands are grated and washed like the potatoe, they yield the arrow 

 root of commerce. From the root of the Manioc, the cassava is pro- 

 cured by a similar process, and this, when dried by agitation on a hot 

 plate, is the tapioca of the shops. By this method of drying, both sago 

 and tapioca undergo a partial change, which will be explained in a sub- 

 sequent section (see p. 113.) 



The substances to which these several names are given are, when 

 pure, similar in their properties, and identical in their chemical consti- 

 tution. They are all colourless, tasteless, without smell, when dry 

 and in a dry place may be kept for any length of time without under- 

 going alteration, are insoluble in cold water or alcohol, dissolve readily 

 in boiling water, giving a solution which gelatinizes (becomes a jelly) 

 on cooling — and in a cold solution of iodine* they all become blue. 



When dried at 212°, they consist, according to Dr. Prout, with wliose 

 analysis those of other chemists agree, of 



Carbon 44-0 per cent., or 12 atoms. 



Hydrogen .... 6-2 per cent., or 10 atoms. • 



Oxygen ..... 49-8 per cent., or 10 atoms. 



100 

 Starch, therefore, may be represented by the formula C^a Hjo Oio» 

 which is identical with that deduced in the preceding section for the 

 cellular fibre of Payen. Both substances, therefore, contain the same 

 elements (carbon, hydrogen and oxygen), united in the ^ame propor- 

 tions, and in both, as well as in the common fibre of wood, the hydrogen 

 and oxygen exists in the proportion to form water. 



That starch constitutes a large portion of the weight of grains and roots, 

 usually grown for food, will appear from the following table, which ex- 

 hibits the quantity present in 100 lbs. of each substance named : 



Starch per cent. 



Wheat flour 39 to 77 



Rye ♦* 50 to 61 



Barley " 67 to 70 



Oatmeal 70 to 80 



Rice flour 84 to 85 



Maize •♦ 77 to 80 



Buckwheat 52 



Pea and Bean meal 42 to 43 



Potatoes, containing 73 to 78 of water, . 13 to 15 

 It thus exists most largely in the seeds of plants, and in some roots. 

 It is frequently deposited, however, among the woody fibre of certain 

 trees, as in that of the willow, and in the inner bark of others, as in 



• Iodine is a solid substance, of a lead-grey colour, possessed of a peculiar powerftil 

 odour, and forming when heated a beautiful violet vapour. It exists in small quantity in sea 

 water, and in some marine plants. Its solution in water readily shows the presence of 

 starch, hy the blue colour it imparts to i;. 



