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As to the heat required, silicates may be produced in the moist way at about incipient red heat, whereas to form the same in the dry way would require a much higher temperature.
As the material melts the lime and silicates form a slag which fuses rapidly and covers the iron and steel in the crucible, so that the molten bath is protected from the action of the gases which are liberated and the oxygen in the atmosphere.
Again, though I consider it desirable to defer the application of soluble silicates until vegetation has made a fair start in the spring, yet in one instance I delayed the application of it so long that there was not moisture to dissolve it until the end of June, and then the plant began to send up suckers from the roots, and the crop was seriously injured by it; but this was in an exceedingly dry spring, and may not happen again for many years.
If we furnish the soil with ammonia, and the phosphates, which are indispensable to the cerealia, with the alkaline silicates, we have all the conditions necessary to ensure an abundant harvest. The atmosphere is an inexhaustible store of carbonic acid.
Hypersthene. Bronzite. Olivine. Olivine. The minerals which form the chief constituents of these igneous rocks are few in number. Next to quartz, which is nearly pure silica or silicic acid, the most important are those silicates commonly classed under the several heads of feldspar, mica, hornblende or augite, and olivine.
An analysis of the Nile alluvium, which has accumulated in the course of ages to a thickness of from three to four feet above the old river-bed, shows that it contains a considerable percentage of such fertilising substances as carbonate of lime and magnesia, silicates of aluminum, carbon, and several oxides. Where the water has to be raised to higher levels, two processes are used.
The northern cases are numbered from 31 to 37. In the first case are varieties of felspar; in the second case are micaceous and other mineral substances; in the third case are basaltic hornblende, tremolite, &c.; in the fourth case are varieties of asbestus, which defies the action of fire; jeffersonite; jenite from the Elba, &c.; in the fifth case are various pyroxenic minerals; in the sixth case are various kinds of garnets, including the lime and chrome varieties; and in the 37th case are the silicates, including beryls, and the emerald.
About this age, probably, when really dry land began to appear, came the first formation of mineral lodes, and the waters, heavily charged with silicates, carbonates of lime, sulphides, etc., in solution, commenced to deposit their contents in solid form when the heat and pressure were removed.
The cerealia require the alkalies and alkaline silicates, which the action of the lime renders fit for assimilation by the plants. If, in addition to these, there is any decaying organic matter present in the soil supplying carbonic acid, it may facilitate their development; but it is not essential to their growth.
For hard stones, such as sand and free stones, rock, etc., the solution should mark 7° to 9° Baume; for soft stones with coarse grit, 5° to 7°; for calcareous stones of soft texture, 6° to 7°. The last coating should always be applied with a more dilute solution of 3° to 4° only. Authorities are divided upon the successful results of the preservation of stone by silicates.
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