68 THE POTATO CHOP. 



there occur in large proportions. They are by Mr. Thos. J. 

 Herapath, and include five different varieties, all grown 

 under exactly the same conditions of soil and climate. 



If we take the foregoing analyses as the bases of our 

 calculations, and assume that an average crop of potatoes 

 consists of 8 tons of tubers and say 3 tons of tops, the 

 former of which are removed from the field and the latter 

 left on it, we should find that it had abstracted from the soil 

 about 175 Ibs. of mineral or inorganic matter, in about 

 the following proportions : 



Potash, 90 



Soda, 8 



Lime, 5 



Magnesia, 8 



Sulphuric acid, 34 



Phosphoric acid, '20 



Chlorine, 10 



175 



The organic composition of the potato is that, however, 

 in which we are more directly interested, as upon that 

 depends the value of the tubers to us, either as articles of 

 food or for manufacturing purposes. 



The potato contains water, albumen or caseine, starch, 

 gum, sugar, fatty matters, fibre, and certain inorganic or 

 mineral matters which have just been described; and the 

 proportions of all these several substances vary greatly 

 with the different varieties and the different conditions as 

 to soil and climate under which they are grown. We 

 have, however, enough evidence, deduced from the great 

 number of analyses that are before us, to assign some- 

 thing like an average composition for the potato, which 

 may be given as follows : 



Water, about 75'00 



Nitrogen compounds (as album en, &c.),.. 2'00 



Starch, IS'OO 



Gum and sugar, ,, 1'75 



Fatty matters, '25 



Fibre, ,, 5'00 



Ash, 1-00 



10000 



