If, however, phosphoric acid is present in the original substance,we may here obtain a precipitate of the phosphates of the remaining metals, together with aluminium, chromium and ferric hydrates.
Bog iron ore is an impure limonite, usually formed by the influence of micro-organisms, and containing silica, phosphoric acid and organic matter, sometimes with manganese.
The phosphates of aluminium, chromium and iron are precipitated, and the solution contains the same metals as if phosphoric acid had been absent.
Although, therefore, different, and sometimes very large, amounts of these typical mineral constituents are taken up by the various crops of rotation, there is no material export of any in the saleable products, excepting of phosphoric acid and of potash; and, so far at least as phosphoric acid is concerned, experience has shown that it may be advantageously supplied in purchased manures.
Sir John Murray finds the source of the phosphoric acid to be the decomposition of large quantities of animal matter, and he illustrates this by the well-known circumstance of the death of vast shoals of fish when warm Gulf-Stream water displaces the cold current which usually extends to the American coast.
He explained and simplified the process of obtaining phosphorus from urine, and made some admirable observations on phosphoric acid; but though he noted the increase in weight that attends the conversion of phosphorus into phosphoric acid he was content to remain an adherent of the phlogistic doctrine.
Some other glycerides isolated from natural sources are analogous in composition to tristearin, but with this difference, that the three radicals which replace hydrogen in glycerin are not all identical; thus kephalin, myelin and lecithin are glycerides in which two hydrogens are replaced by fatty acid radicals, and the third by a complex phosphoric acid derivative.
If phosphoric acid is absent, aluminium, chromium and ferric hydrates are precipitated.
That it shall have a great excess of the strong base, ferrous oxide, FeO, for the phosphoric acid to unite with, lest it be deoxidized by the carbon of the iron as fast as it forms, and so return to the iron, following the general rule that oxidized bodies enter the slag and unoxidized ones the metallic iron.
In the basic Bessemer process, also, unforeseen variations in the siliconcontent are harmful, because the quantity of lime added should be just that needed to neutralize the resultant silica and the phosphoric acid and no more.