AND AGRICULTURE. 77 



of starch, eighteen pounds of gluten, and six 

 pounds of oil. 



The principal constituent of potatoes and tur- 

 nips is water. Of the first, one hundred pounds 

 contain seventy-five pounds of water ; and of the 

 second, one hundred pounds yield about eighty- 

 eight pounds of water. The quantity of starch 

 in potatoes is about fifteen to twenty pounds to 

 the hundred pounds. 



The proportions of the several substances con- 

 tained in different lots of the same kind of pro- 

 duce will often be found to vary considerably. 

 Some samples of wheat may contain more gluten, 

 some varieties of oats more oil, and some kinds 

 of potatoes more starch. 



We have already seen that when vegetables 

 or grain are burned there remains a small quan- 

 tity of inorganic matter, or ashes. The ashes 

 contain the phosphates of potash, soda, lime, and 

 magnesia ; they also contain common salt, and 

 some other saline substances. 



Questions. How much water do one hundred pounds 

 of potatoes contain ? How much in one hundred pounds of 

 turnips ? How much starch in one hundred pounds of pota- 

 toes ? Do different lots of the same kind of grain always 

 contain the same proportion of starch, fat, &c. ? 



7* 



