Report on the Analysis of the Ashes of Plants. 595 
A knowledge of the mineral composition of every plant and 
each part of such plant, would be the only sure guide to the use 
of artificial manures — more especially those of an entirely mineral 
character. 
It would enable us to add to the soil exactly that which we 
had taken from it. In the case of the cereals we should know 
that in every bushel of wheat or barley we had removed from the 
soil so much potash, so much silica and phosphoric acid, which 
must in some shape or other be returned ; for we hold it to be 
no less the duty than the interest of the farmer to restore to his 
fields an equivalent for the mineral matter of which he robs them 
in the grain sent into the large towns, of which at present nothing 
is returned. 
. It is true that many soils ai-e found when the time for the corn 
crop comes round possessed of the requisite materials for ils 
perfect growth ; these having by the action of the intervening 
green crops become fitted to serve as food for the cereal. But it 
is not wise to trust to this, and it is not just to remove from the 
land twice in every four or five years, as the case may be^ valu- 
able mineral matter which is in no way replaced.* 
The use of bones for the turnip crop is a partial but most 
valuable restitution, and the further addition of silicate of potash 
at some period of the rotation would probably be attended with 
similar advantages. 
But whilst all the materials of the grain are for the most part 
lost to the soil, the mineral matter of the straw and the chaff finds 
its way without much loss back to the land from the manure 
heap. And this leads us to remark that a thorough acquaintance 
with the mineral constitution of all cultivated plants will afford 
a corresponding amount of information respecting the inorganic 
contents of natural manures. For the manure formed from a ton 
of turnips or a ton of hay must contain the mineral matter of 
these crops, deducting that trifling proportion which in the 
case of growing animals is retained for the formation of their 
bones, &c. 
From the known composition of different parts of plants, we 
might be led to apply them to particular purposes in farm 
economy, and the manure thus formed might be kept apart and 
reserved for special applications. Thus Boussingault informs us 
that the bran of wheat, which, according to his experiments, con- 
stitutes on an average from 13 to 20 per cent, of the dry wheat, 
* Some allowance must be made for this statement in cases where 
foreign substances (as oil-cake) are introduced into a farm ; the mineral 
matter contained in these is eventually added to the soil, and is some, 
although an inadequate, compensation for that carried off in the grain 
crops. 
