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the radicle fibres of plants. The vegetable alkali 
likewise has a strong attraction for water, and even 
in small quantities may tend to give a due degree 
of moisture to the soil, or to other manures ; though 
this operation, from the small quantities used, or 
existing in the soil, can be only of a secondary 
kind. 
The mineral alkali or soda is found in the ashes 
of sea-weed, and may be procured by certain che- 
mical agencies from common salt . Common salt 
consists of the metal named sodium, combined with 
chlorine ; and pure soda consists of the same metal 
united to oxygene. When water is present which 
can afford oxygene to the sodium, soda may be 
obtained in several modes from salt. 
The same reasoning will apply to the operation 
of the pure mineral alkali, or the carbonated alkali, 
as to that of the vegetable alkali ; and when com- 
mon salt acts as a manure, it is probably by enter- 
ing into the composition of the plant in the same 
manner as gypsum, phosphate of lime, and the 
alkalies. Sir John Pringle has stated, that salt in 
small quantities assists the decomposition of animal 
and vegetable matter. This circumstance may 
render it useful in certain soils. Common salt 
likewise is offensive to insects. — That in small 
quantities it is sometimes a useful manure, I believe 
is fully proved ; and it is probable that its efficacy 
depends upon many combined causes. 
Some persons have argued against the employ- 
ment of salt ; because when used in large quan- 
tities, it either does no good, or renders the ground 
sterile ; but this is a very unfair mode of reasoning, 
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