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X. — On Modes of Comparing the Nutritive Values of different 
Crops. By W. H. Hyett. 
It is well known tliat different esculent roots, and probably dif- 
ferent varieties of the same root, differ in their weight with refer- 
ence to equal bulks; and there are some reasons for thinking 
that this difference (called their specific gravity) might,* when 
ascertained, afford an easy, though somewhat rough, method of 
estimating some of their relative powers of nourishment. Water, 
with sugar, starch, gluten, and albumen, are the constituents which 
make up, with trifling exceptions, the mass of our common agri- 
cultural roots. In 1000 parts of the potato more than 700 are 
water. About 274 have been found to be composed of the above- 
named vegetable principles, said to be positively nutritious — the 
remainder consisting of a very trifling amount of soluble salts, and 
still less of insoluble earths and oxides. In the same manner 
1000 parts of mangold wurzel, of swedes, and of turnips, give by 
analysis respectively 139, 64, and 42, of these nutritive ingredi- 
ents — the large proportion of the remainder being water, with 
which all the pores of a healthy and perfect root, when fresh taken 
from the ground, seem to be filled. Though it must perhaps be 
admitted that the elements of water, as food, have some effect on 
the animal economy, it is the other constituent principles of vege- 
• The published tables of specific gravities enumerate a great variety of 
stones, metals, woods, earths, salts, acids, oils, gases, wines, &c., with many 
of which the specific gravity is used as the best practical measure of their 
various qualities. The amount of nutritious ingredient contained in milk 
and wort is measured by an instrument expressly made to take the specific 
gravity. But in none of these lists can I discover that any of our agricul- 
tural productions are noticed ; nor in our best and most recent works on 
these subjects, such as Thomson's 'Vegetable Chemistry,' where 35 of the 
" principal roots employed in medicine and the arts " are treated of, can I 
find the general proportions of the proximate principles of any of our com- 
monest agricultural roots, with the exception of the potato, and yet these 
principles are supposed to contain the primary essentials of all animal nou- 
rishment. It is true the proportion of sugar in beet, and the peculiar 
proximate composition of carrot juice, is given chiefly from the elaborate 
investigations of Eynhoff, but no notice whatever is taken of the turnip, 
swede, nor (except that of beet) of any of the varieties of mangold wurzel. 
T by no means presume to point to this omission as any disparagement of 
works of such research and reputation. The information seems not to have 
been required by those most interested, and consequently has not been 
thought worth making public. It cannot be doubted, now that agriculture 
invites the attention of so many eminent men, that all such deficiencies will 
soon be supplied. Dr. Daubeny's table of the 'Constituents of Crops,' com- 
piled from the works of Boussingault and Sprengel, and published in the 
last volume of the Royal Agricultural Society's 'Journal,' conveys most 
useful information ; but were the proportions of the proximate principles of 
vegetables appended, it would be rendered far more valuable. — W. H. H. 
