Mineral Manures and Manuring. 
285 
stituent of bones ; and in accordance with his mineral theory, 
which is still greatly misunderstood, he advised that the bones 
should be dissolved with sulphuric acid. The preparation of 
superphosphate, which was thus based upon purely theoretical 
principles, has stood the test of experience. The manufacture of 
artificial manures at the present day consists almost exclusively 
in the preparation of superphosphate, and is an important 
industry in nearly every civilised country. 
This advice of Liebig's caused Mr. Lawes to commence 
experiments on superphosphates, which he has continued up to 
the present day. It may without hesitation be said that these 
experiments at Rothamsted have done more towards the practical 
solution of the mineral theory, and the promotion of a rational 
system of manuring-, than has been done at any other experi- 
mental station. Although the quantities of manure which have 
been used are neither economical nor practical, yet, so numerous 
and varied are the experiments that they supply a clear practical 
answer to almost every question. Were it not for these experi- 
ments of Messrs. Lawes and Gilbert we should at the present 
day merely know that crops were benefited by the addition of 
superphosphate and potash, either separately or together, whether 
with or without ammonia. As to what are the conditions 
under which this improvement takes place, what crops are most 
benefited, and how the individual factors act in a long series of 
years — on all these points we should still know nothing. 
Upon the discovery and opening of the rich potash-beds in 
Germany, Liebig pointed out the necessity of adding potash to 
manures. Its use was unprofitable 30 years ago because it was 
not then an article of commerce, and subsequently when em- 
ployed it became unprofitable because it was applied in excessive 
and irrational quantities. If employed in limited quantities, 
it will be no longer unremunerative, but as profitable and as 
necessary for the cultivation of light soils as is superphosphate. 
Even where phosphates alone operate, their action is generally 
augmented by the addition of potash-salts, because the amount 
of potash naturally in the soil is not sufficient to bring the 
whole of the phosphates into operation. 
A series of experiments, conducted at Rothamsted, shows how 
great is the action of potash combined with phosphates upon 
permanent pasture, even on a heavy soil. 
These experiments are not all that could be desired, because 
only for the last two years do we know the total produce of 
the plots. We may, however, draw definite conclusions from 
the preceding years, when the hay-harvest alone was gathered 
in, and the aftermath eaten off, if we suppose the aftermath to 
be equal to half the yield of hay. 
