CHEMISTRY OF THE POTATO. 



69 



Arranging these several compounds in the manner al- 

 ready adopted with the other crops, they would stand 

 thus: 



Compounds containing nitrogen (flesh -formers), 2'QO 1 



Compounds not containing nitrogen (heat-givers and fat-formers), 



as starch, 15'00 



gum, sugar, fat, &c., 2'00 



fibre, 5-00 



Ash (mineral matters), 1-00 



Water, 75'OQ 



100-00 



The proportion of nitrogen compounds present would 

 indicate rather a low feeding value to the potato, not 

 superior, indeed, to that of the turnip or mangold, were 

 it not for the large proportion of starch present, in addi- 

 tion to the other carbonaceous compounds, as gum, sugar, 

 &c. These make up the proportion of its solid consti- 

 tuents to about 25 per cent., or about double that of 

 the roots referred to. 



For all purposes of consumption, however, whether as 

 food or for economic use, the starch is the compound of 

 most importance to us, and upon the proportion of this 

 substance contained in the tuber we are accustomed to 

 base our estimate of its value. 



In this we find great variations exist, for instance 



New Potatoes contained 5'53 per cent. 2 



South Americans, 

 Ash-leaved Kidneys,. 



Ked Dons, 



White East Lothian 



Bed Ayrshire, 



Bed Lanark, 



Cups Argyleshire, ... 



Ked Perthshire, 



Orkney Potatoes, 



Cups (unknown) , 

 Buffs Forfarshire, .. . 



Canadians, , 



Cups Mid-Lothian, . 



8-14 

 9-52 

 1075 

 12-24 

 13-08 

 14-08 

 15-14 

 16-53 

 17-42 

 18-94 

 20-71 

 20-92 

 23-82 



1 Johnston gives 1'41 per cent, as the mean of several analyses, Horsford 

 and Krocker give 2*43 per cent, as the mean proportion of nitrogen compounds. 



2 " Chemical Investigation of the Potato," by Dr. Fromberg. High. Soc. 

 Trans., 1847, p. G69. 



