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loam, and many different modifications of clay in soils. In 
their natural state they may be boiled in concentrated sulphuric 
acid, without sensible change ; but, if feebly burned, as is done 
with the pipe clay in many alum manufactories, they dissolve 
in the acid with the greatest facility, the contained silica being 
separated like a jelly in a soluble state. Potters’ clay belongs 
to the most sterile kinds of soil, and yet it contains within itself 
all the constituent elements essential to a most luxurious 
growth of plants; but their mere presence is insufficient to 
secure this end. The soil must be accessible to the atmos- 
phere, to its oxygen, to its carbonic acid ; — these must pene- 
trate it, in order to secure the conditions necessary to a happy 
and vigorous development of the roots. The elements present 
must be brought into that peculiar state of combination which 
will enable them to enter into plants. Plastic clay is wanting 
in these properties; but they are imparted to it by a feeble 
calcination.” 
“At Hardwicke Court, near Gloucester, I have seen a garden 
(Mr. Baker’s) consisting of a stiff clay, which was perfectly 
sterile, become by mere burning extremely fertile. The oper- 
ation was extended to a depth of three feet. This was an 
expensive process, certainly ; but it was effectual.” 
“The great difference in the properties of burnt and unburnt 
clay is illustrated by what is seen in brick houses, built in moist 
situations. In the town of Flanders, for instance, where most 
buildings are of brick, efflorescence of salts cover the surfaces of 
the walls, like a white nap, within a few days after they are 
erected. If this saline incrustation is washed away by the 
rain, it soon re-appears ; and this is even observed on walls 
which, like the gateway of Lisle, have been erected for centuries. 
These saline incrustations consist of carbonates and snlphates, 
with alkaline bases; and it is well known these act an impor- 
tant part in vegetation. The influence of lime in their pro- 
duction is manifested by their appearing first at the place 
where the mortar and brick come into contact.” 
“ I have now, I trust, explained to your satisfaction, that 
the mechanical operations of agriculture, — the application 
of lime and chalk to lands — and the burning of clay, depend 
upon one and the same scientific principle : they are means of 
accelerating the decomposition of the alkaline clay silicates, in 
