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VI. — On the Tlieoretical and Practical Value of Purchased Foody 
and of its Residue as Manure. By Dr. Augustus Voelcker, 
F.R.S. 
In the capacity of Consulting Chemist to the Royal Agricultural 
Society I frequently receive for analysis samples of oilcakes, 
cereal-grains, and other kinds of food for stock, and am requested 
not only to determine their nutritive value but also to express an 
opinion with regard to their money-value. 
The questions put to me may appear simple enough and not 
difficult to answer ; and yet I am bound freely to confess that no 
inquiries are, in my judgment, more difficult to answer satis- 
factorily than those with respect to the comparative money-value 
of various articles of food. 
There is no difficulty in determining by analysis with toler- 
able precision the fertilising and commercial value of guano, 
sulphate of ammonia, nitrate of soda, superphosphate of lime, 
and other portable manures, because the commercial value of 
artificial manures depends mainly upon their composition. The 
amount of ammonia, nitric acid, soluble and insoluble phos- 
phate of lime, or potash, in a manure, can be ascertained with 
certainty by analysis. The various constituents upon which 
the fertilising properties of the various kinds of artificial manures 
mainly depend may either be bought separately — some in the 
form of simple saline compounds, others in commercial products, 
which, like dried blood or wool-refuse, owe their fertilising 
properties to the nitrogen they contain — or they may be pur- 
chased in articles of commerce, which, like bone-dust, contain 
more than one manuring element. In either case, we have to do 
with commercial products, the money-value of which is regulated 
by the kind and amount of the real fertilising constituents con- 
tained in them ; and although the market-price of ammonia or 
of phosphate of lime, &c., is subject to fluctuations, the money- 
value of compound artificial manures can, nevertheless, be ascer- 
tained by analysis with sufficient precision to guard the purchaser 
against frauds on the part of the dealer. 
But a far more difficult case is submitted to the agricultural 
chemist when he is requested to analyse an article of food and 
to give an opinion of its nutritive and money-value. By appro- 
priate analytical processes the proportions of starch, albumen, 
gluten, oil, woody-fibre, and other constituents which enter into 
the composition of feeding-stuffs, may be determined readily 
enough ; but as these constituents are not sold separately in a 
form in which they may be used economically by the feeder of 
stock, it is not possible to assign a separate money-value to them. 
