114 



THE COMPOSITIOX OF CROPS IN 



than nine-tenths of this latter consist of water, whereas the 

 grain consists of what may be called dry matter. If we bring 

 them to a level in this respect, we have 2016 lbs. of the one, 

 and 4032 lbs. (or as it happens, just double the weight) of the 

 other. But this immense quantity of water in the turnip crops 

 does not exist there as pure water (although the chemist can 

 draw it off as such in his hot-water bath) ; it is in intimate 

 combination with a large amount of organic matter, and holds 

 in solution, so to speak, a large amount of mineral salts. If 

 we reduce the dry matter in both cases to '' ash," we get ten 

 times as much from the turnips as we get from the grain : or, 

 in point of fact (taking the average of ash), we get 34 lbs. in 

 the one case, and 350 lbs. in the other. But, reverting to the 

 phosphoric acid per cent, in each, — one-tenth of 350 is just some- 

 thing^ more than twice as much as one-half of 34. The round 

 numbers here used come pretty near the averages — which we 

 must take in all such cases ; — but the ash of wheat does not 

 contain quite 50 per cent., but only 45 per cent, of phosphoric 

 acid, whereas the ash of turnips contains pretty exactly 10 per 

 cent, of that substance. In this case the difference in the amount 

 of ash yielded by the two crops is very great ; but even when there 

 is no such difference in the gross amount of ash which the crops 

 yield, and when we compare one cereal crop with another, we 

 find that the relative percentage of a substance in the ash does 

 not indicate the relative amount of that substance which the 

 crop draws from an acre of land. But, before makinof such 

 comparison, it seems necessary for the sake of clearness, and by 

 way of illustration of what has just been said, and of what we 

 propose to add, — to note down in the usual form the composition 

 of the ash of three of our most common crops as follows : — 



Composition of oxe hundred parts of Ash. 



