NORTH-CAEOLINA GEOLOGICAL SURVEY. 67 



LB8. 



Phosphoric acid, 12.00 



Sulphuric acH, 0.30 



Chlorine, trace, 



Lime, 0.80 



Magnesia, 4.00 



Potash and soda, 7.00 



Silica, 0.04 



Oxide of iron, 0.00 



In the straw the proportions are : 



Phosphoric acid, 5.00 



Sulphuric acid, 1.50 



Chlorine, 1.00 



Lime, 15.00 



Magnesia, 9.00 



Potash and soda, 17.00 



Silica, 121.00 



Oxide of iron, 1.75 



One remark may be made in this place, that the phosphoric- 

 acid of the grain greatly exceeds that of the straw ; while 

 the lime of the straw is in much greater proportion than it is 

 in the grain, and the silica is reduced in the grain to the 

 smallest percentage, but greatly abounds in the straw. We 

 have in this, as in many other instances, the exercise of a 

 species of elective affinity, by which the elements select their 

 appropriate organic materials. 



A potatoe crop, when dried, weighs, in tubers, 2828 Ibs., 

 and gives, in ashes, 4 per cent., and weighs 113 Ibs. per acre. 

 The percentage of composition is : 



LB8. 



Phosphoric acid, 13.00 



Sulphuric acid, 8.00 



Chlorine, 3.00 



Lime 2.00 



Magnesia, 6.00 



Potash and soda, 58.00 



Silica, 6.00 



Oxide of iron, 17.00 



The percentage in tops, 5042 Ibs., with 6 per cent, of ash, 



