INVESTIGATION OF SOILS. 
227 
The muriates of soda and of lime are detected by nitrate of silver, which 
carries down the muriatic acid : and the ammonia is developed by a separate 
process, upon a fresh portion of soil, by means of caustic soda and quick lime. 
All soils contain iron ; but in some it exists in the lower state of oxidation, 
called protoxide, and then the tint of the loam is of a pale or greyish-drab ; in 
others, the red, purple, or rich brown hue indicates its saturation with oxygen. 
These conditions can be ascertained by the test commonly termed prussiate of 
potassa, added to a solution of the soil in muriatic acid. When the iron exists as 
a protoxide, it appears as a pale bluish precipitate ; but the peroxide yields the 
deep tint of Prussian blue, which, in fact, is produced by the action of the 
Prussiate. 
This test is most delicate, and may be relied on as an indicator of iron when in 
acid or neutral solutions of soil ; but it is not now used as the precipitant 
in analysis. 
Peat — that is, properly speaking, heath or moor-soil — contains some iron, 
generally in the lowest state of combination with oxygen ; and this is readily 
accounted for by the presence of black vegetable matter as one of the chief 
components of such earths. It may not be required to analyse these soils by 
chemical tests, because combustion at a red heat in an open capsule or evaporating 
basin will suffice to carry off the vegetable organic matter, leaving the bulk of 
white sand — so abundant in such soils — remaining in the vessel, combined with 
the oxide of iron. But the investigation by fire should always be made, as thereby 
the proportions of the sand and organic substances that exist in different samples 
will be determined. A curious and instructive series of experiments can be made 
with heath-soils, by digesting an ounce of each in half a pint of boiling rain-water, 
adding to one sample a few grains of salt of tartar, or soda ; to another, a few 
drops of caustic ammonia : a deepening of tint will immediately take place, owing 
to the action of the alkalies upon the humic extractive of the soils. The infusion 
being strained off through a piece of coarse muslin, will be found, in some instances, 
of the colour of porter ; but by the addition of a little quick lime, or even of strong- 
lime-water, this tint will disappear, the humic matter being most strongly 
attracted by the lime, uniting with it as humate of lime, and falling as an insoluble 
precipitate. These experiments teach us the true use of lime in land over glutted 
with vegetable matter ; it acts as a specific corrective, by combining with the 
redundant matters which poison the soil of a garden, and render bog and peat- 
lands quite barren. 
Leaf -mould — always rejecting that of the laurel — is a good substitute for 
heath-soil, provided it be mixed with abundance of pure white, silicious sand. 
Tested chemically by alkalies, it will yield colouring matter, which is acted upon 
and precipitated by lime, as in the case above alluded to. But there is one 
circumstance which must not be overlooked. Leaves of trees that grow in loams 
contain definite proportions of lime, alkalies, iron, and other of the earths soluble 
