Agricultural Chemistry. 
467 
ment." Whereas our own statement is, that, however small the 
amount of phosphates contained in a removed crop of turnips, 
they require a large amount for their development. And if it be 
really a well-established fact, that, however small may be the 
quantity of phosphates lost to the farm by the growth of turnips, 
still a much more liberal supply is required in the soil for the 
production of a full agricultural crop of them than of corn, it is 
then obviously impossible, that the progressive exhaustion of the 
phosphates, could be the cause of the extended cultivation of the 
former. In fact, there can be no doubt, that such an exhaustion 
would be a far greater obstacle to the extended growth of roots 
than of corn. 
But with regard to the effects of an artificial supply of phos- 
phates, upon the increased production of corn, Baron Liebig 
further says : — 
"We believe that the importation of 1 cwt. of guaiw is equivalent to the 
importation of 8 cwt. of wheat ; the hnndredwcight of gnano assumes in a 
time which can be accurately estimated, the form of a quantity of food 
corresponding to 8 cwt. of wheat. The same estimate is applicable in the 
valuation of bones. 
" If it were possible to restore to the soil of England and Scotland the phos- 
phates w'hich during the last fifty years have been carried to the sea hy the 
Thames and the Clyde, it would be equivalent to manuring with millions of 
hundredweights of bones, and the inodiice of the land ivoidd increase one- 
third, or perhaps double itself, in five to ten years. 
"We cannot doubt that the same result would follow -i/" i/(e pn'ce of the 
guano admitted the application of a quantity to the surface of the fields, con- 
taining as much of the 2)hosphates as have been ivithdrawn from them in the 
same period." — Letters, 3rd edition, pp. 523, 524. 
How far the increase in the produce of wlieat by the use of 
guano, is measurable by the amount of phosphates it supplies, 
the practical farmer may judge from the fact, to which we have 
before called attention, namely, that 1 cwt. of Peruvian guano loill 
supphj as much phosphoric acid as would be contained in about 18 
bushels of wheat and their equivalent of straw, say 1800 lbs.; and 
that of nitrogen, 1 cwt. of guano will contain about as much as 
11 bushels of wheat and 1100 lbs. of straw. But, if we were to 
assume, that one-third to one-half only, of the nitrogen supplied 
in manure for the growth of wheat will be obtained in the in- 
crease produced, we should have on this calculation, 4 or 5 
bushels of corn, and their equivalent of straw, by the use of 1 
cwt. of guano. We leave it with the practical man to judge, 
whether these last amounts, or 18 bushels of corn with their 
equivalent of straw, are more nearly those which in practice he 
obtains, by the use of 1 cwt. of guano. 
Baron Liebig proceeds : — 
" If a rich and cheap source of phosphate of lime and the alkaline phos- 
phates were open to England, there can be no question that the imiiortation 
