RECAPITULATION. 63 



RECAPITULATION AND GENERAL REMARKS ON THE FOREGOING ANALYSES. 



1. It will be observed that the potato contains a large percentage of water, averaging 



seventy-one or two per centum. In this respect it exceeds the cereals, and hence is 

 inferior to them in equal weights as a nutritious food. It contains, however, less 

 water than the beet, carrot or turnip ; and there is a closer resemblance in composi- 

 tion between the potato and the cereals, than between the latter and the other root 

 crops. The potato, for instance, contains a large amount of starch, an element 

 which renders it a highly important article for food. The potato furnishes, in the 

 chlorides which are formed in the analyses, phosphates possessing the same characters 

 as that found in the grains, a phosphate which is insoluble in water, and fusible at a 

 low red heat. This is not found, however, where the phosphoric acid is obtained in 

 combination with a base, as iron. It is not thrown down by ammonia, with phosphate 

 of iron, lime and magnesia, and hence appears among the last results of analysis in the 

 chloride. I have given it as insoluble matter in the chlorides. It contains a trace of 

 silex and phosphate of lime, but consists of phosphate of potash and soda. The grains 

 and the potato always furnish this product, in which respect they resemble each other ; 

 but the beet and carrot, though they may give a small amount of insoluble matter, yet 

 it consists principally of soluble silica and organic matter. 



2. The nitrogenous matters, in an equal weight of the potato and the cereals, are much 



less in the former ; yet the latter give a greater amount upon the acre. This fact, it 

 appears to me, decides the question as to the real value of the crop. The percentage 

 of the nitrogenous or proteine bodies, as they are usually termed, appear small when 

 compared with the other elements, or with those of the grains : they rarely amount 

 to more than 1" 50 or 2 per centum. The albumen and casein, which represent the 

 proteine bodies, seem liable to some considerable variation by circumstances. They 

 are liable, for example, to spontaneous changes in the course of the analysis ; for, in 

 some instances, very little albumen is obtained, and the whole product for proteine 

 matter may be coagulated and thrown down by acetic acid. This result, however, 

 does not alter or change the fact in regard to their existence in the potato. It will be 

 observed, also, that there are differences in the amount of albumen and casein in dif- 

 ferent varieties. For cooking, and suiting the palate, it is not perhaps necessary that 

 the kind of potato should be that which is richest in proteine compounds ; but for 

 feeding stock, it is a matter of more consequence. I doubt much, indeed, whether 

 the use and value of the starch in this esculent is well understood ; that it is merely 

 intended for the support of respiration and animal heat, may well be doubted. These 

 purposes, it is true, are important, and highly so ; still, animals fatten rapidly upon 

 potatoes. We may, I think, without danger of falling into a gross error, admit that 

 the nutritive properties of the potato are not due alone to the proteine bodies. 



