200 
my which alkaline matter seems destined to perform. 
The experiments of Mr Davy prove that lime, as 
well as alkali, is present in the vegetable fluids * ; 
and it has been shewn to exert similar effects on the 
colourable juices (401.) of the leaves; so that we 
possess evidence, not only of its existence in the plant, 
but of its capacity to effect a necessary change in the 
vegetable juices. Such views explain why lime is 
useful in every kind of soil that is deficient in calca- 
reous matter ; and account, also, for its gradual dis- 
appearance or exhaustion. Is the large quantity of 
alkali, which green vegetables afford, obtained only 
in some compound form, from potassa existing in the 
earth ? or, in the process of vegetation, is lime, 
which resembles it in so many of its properties, ac- 
tually transmuted into it ? The more hidden secrets 
of nature are but just beginning to be disclosed ; and 
the dreams of alchemy are, perhaps, destined to take 
form and substance, from the researches of modern 
chemistry. 
473. The analogy between the chemical operation 
of the different electricities of the Voltaic pile, and 
the calorific and chemical rays of light, which we 
have thus endeavoured to support, will, we conceive, 
derive confirmation from the results of certain elec- 
trical experiments, which have been made on vege- 
table matters. For the different electricities rapidly 
change vegetable colours, by developing, in all 
cases, as we believe, acid or alkaline matter, precise- 
Phil. Trans. 1807. 
