10 ANALYSIS OF SOILS. 
should be accurately weighed, and it is convenient to take some determined 
quantity of grains, as 1000, 500, or 250, according to the accuracy of the 
instruments at hand. This portion should be put into a shallow earthen or metal 
vessel, and heated over the fire or a lamp, for about ten minutes, stirring it with a 
chip of dry wood : the heat should not be so great as to discolour the wood. It 
may then be allowed to cool, and be weighed again : the loss of weight indicates 
the water which remained uncombined after the soil appeared quite dry : this is 
the first thing to be noted." 
The power of retaining water is insisted upon with great judgment : a certain 
quantity of it may be held pertinaciously, without the least appearance of moisture, 
but this capacity is not the same in all the earthy constituents, the matter of pure 
clay (alumina) possesses it in the highest degree, that of pure flint (silex) in the 
lowest : hence the rapidity with which sands become parched and arid. Chalk 
retains water with great energy ; and it is from an experimental knowledge of this 
fact that we are able to account for the verdure which prevails in chalky districts 
during hot dry summers, when the pastures and grass lands over clays and gravel 
are scorched by the sun's power. 
The substance, which of late years has been called humus, is stated to be 
most retentive of water ; it is that residual, decomposable body, which results from 
the fermentation of the dunghill, and the laboration of the vegetable, fibrous 
matters in old turf-heaps. It is not earth, properly considered as such, nor can 
we define, accurately, what is its real nature ; for humus cannot be imitated by 
the art of man. Correctly speaking, it is a product of the ground ; for, although 
the blackened spit-dung of the mixen contains, or rather is itself the essence of 
this singular combination of carbon, oxygen, and hydrogen, yet it requires the 
presence of the earths proper, and the active principle of vegetable life, exerted 
through the radical organs of the gTowing plant, to eftect the due laboration of 
manuring substances, and their conversion into perfect humus. Humus, then, if 
we rightly appreciate its properties and origin, is the aliment of the vegetable 
being, convertible into all its common and laborated juices and secretions ; but 
entirely obscure in its nature, and removed from the ken of man's researches, 
inasmuch as it appears never to be fully formed, until, at the moment of its 
development, it is taken up by the vegetable absorbent system, wherein it is 
immediately converted into sap. 
( To be continued. J 
