SILICA. 219 | 
more abundant in culms, and most plentiful in | use of sulphated bones for the turnip crop might 
_ the sheltering chaff-coats of the ripening grain. | be beneficially followed by a top-dressing of sili- 
The quantity of soluble silica in most soils, | cate of soda upon the young corn of the follow- | 
or of silica under conditions which render it | ing year. But the propriety of incurring the ex- | 
capable of solution and readily available for the | pense of such an application along with bones 
use of plants, is so great as to render special ap- | in all cases is very doubtful. Here also much 
plications of it altogether unnecessary. The small | will depend upon the actual constitution of the 
proportion of it, too, which is carried off by the | soil; for it would be a waste to add anything 
seeds of field crops, and not returned in the por- | which the soil already contains abundantly, and || 
tions of farm-yard manure which consist of | in a state in which it can readily minister to the 
leaves and culms and chaff, is, in general, far | wants of the plant. Now, if a portion of soil be 
more than compensated by the disintegration of | burned, in order to destroy the organic matter 
part of the insoluble silicious constituents of | it contains, and be then boiled in distilled water 
the soil in the operations of fallowing and tillage, | for a length of time, and the filtered solution be 
and by the bringing up of soluble silica from the | afterwards evaporated to dryness, and the resi- 
lower parts of the soil in the absorptive process | due heated to redness to burn off the organic 
of root crops, and allowing it to remain on the | matter, a minute but variable quantity of saline 
| 
field by carrying away only their bulbs or tubers | matter will remain, in which a trace of silica will 
or taps. “ Between corn crops,” as Liebig sug- | usually be found. Most soils, therefore, contain 
gests, “we may grow mangel-wurzel or even | some silica in a state in which it may be taken 
potatoes, if we remove only the tubers of the | up by water. Again, if, after boiling with water, 
latter, and allow the plant itself, which contains | the soil be digested for two or three hours with 
much silica, to remain on the field.” But, in | concentrated muriatic acid till it is perfectly col- 
fact, most fields contain such a large natural | ourless, and if the filtered solution be treated 
store of available silica, that no care respecting | with ammonia and oxalate of ammonia, to sepa- 
it needs to be entertained, and no expedient for | rate the oxide of iron, alumina, and lime, and be 
any special supply of it needs to be adopted, for | then evaporated to dryness, an appreciable quan- | 
centuries to come. Almost the only soils, or at | tity of silica will be found in the saline matter 
least the chief ones, which may now and stated- | which remains. Or,if the acid solution be at 
ly require direct applications of it, are peat lands | once evaporated to dryness, and then treated 
and other predominantly humous grounds, which | with water, some silica will remain insoluble. 
contain a comparatively small proportion of mine- | Soils, therefore, generally contain a further ap- 
ral matter, and which produce such soft and flexu- | preciable quantity of silica, in a state in which 
ous corn-culms as want sufficient strength and | it is soluble in acid solutions.” He then states 
firmness to resist the buffetings of the weather. | that, of five specimens of different soils which 
Yet many scientific farmers, and even some dis- | he analyzed, one contained 0:19 per cent. of 
tinguished agricultural chemists, contend that | silica soluble in acid solutions, another 0°16 per 
artificial silicates should be applied to all soils,— | cent., a third 0:2 per cent., a fourth 0:17 per 
that they form an indispensable ingredient in | cent., and the fifth at top 0°84 per cent., and 
any compound special manure which is intended | at bottom 0°42 per cent.; and he adds :—“I 
to serve as a substitute for farm-yard manure,— | could have given many other such results ; but 
and that they form a fit and sometimes necessary | these show both the presence of silica in this 
preparation for a wheat crop on any land which } state in our cultivated soils, and how much it 
| has suffered an appreciable abstraction of its | varies in different soils. The quantity present 
| soluble silica by the crops of the immediately | in the first and third instances—1-5th of a per 
preceding years. The question thus brought | cent., or one pound in 500 lbs. of soil—appears 
into dispute is one of very considerable practical | very small when compared with the whole soil, 
importance, and requires much knowledge and | and yet it proves to be large when we come to 
very comprehensive thought for its proper inves- | calculate how much an acre of soil will contain, 
tigation. Let us hear the reporter of the Agri- | and how much a crop of corn will carry off from 
cultural Chemistry Association of Scotland upon | that acre. A square yard of soil 12 inches deep, 
it :— will weigh about 700 lbs., so that this extent of 
“Tt may be said by some that guano and | soil will contain 13 lb. of silica soluble in acids, 
bones are both alike deficient in silica, which | which amounts to 6,700 lbs. in an acre! The 
exists so largely in our grasses and in the stems | straw of our grain crops leaves, on an average, 
of our corn plants; and, therefore, that some | less than five per cent. of ash, of which less than 
soluble silicate might with advantage be added | one-half usually consists of silica, and a crop of 
to either of these manures, when crops of corn | straw rarely exceeds 3,000 lbs. per imperial acre. 
are to be improved by them. There is much | If we take these numbers as tolerable approxi- 
show of reason in this when considered theoreti- | mations, the quantity of silica carried off by a 
cally, and there are, no doubt, cases in which an | crop of straw amounts to 75 lbs. per acre, while 
admixture of one-fifth of its weight of silicate of | the silica soluble in acids, and which it is be- 
{ 
the flesh of succulent roots, less scarce in leaves, | soda would improve a guano, or in which the 
| 
