EUCALYPTUS TREES. 57 
being especially needed in the soil for all kinds of root- 
crops, for vine and maize ; nor can most other plants 
live without it altogether, although the quantity re- 
quired may be small; but I must add, for manuring, 
potash by itself would be far too valuable. 
Almost every kind of forage affords potash salts, 
these being among the necessaries for the support of 
herbivorous animals. Their undue diminution in food 
is the cause of various diseases, both in the animal 
and vegetable world; or predisposes, by abnormal 
chemic components of the organisms, to disease. 
The muscles of the human structure require a com- 
paratively large proportion of carbonate of potassa ; it 
is also absolutely required in blood, predominating in 
the red corpuscles. Piants grown in soil of rocks con- 
taining much feldspar—such as granite, gneiss, syen- 
ite, some porphyries, diorite—are always particularly 
productive in potash, potassium entering largely into 
felspatie compounds, The latter mineral yields, in 
most cases, from twelve to fourteen per cent. of po- 
tassa, which, if changed to carbonate, would become 
augmented by nearly one half more. It is fixed chiefly 
to silicic acid in feldspar, and thus only tardily set free 
through disintegration, partly by the chemic action 
of air, water, and various salts, partly through the 
mechanic force of vegetation.* The importation of 
potash into Victoria during 1870 was only one hun- 
dred and seventy tons, but,. with the increase of 
chemic factories, we shall require much more. 
It has justly been argued that the chemic analysis 
affords a very unsafe guidance to the artisan, as re- 
gards the quantity of potash obtainable from any kind 
* The proverb of chemistry — ‘‘ Cerpora non agunt, nisi jluida”’ — is here 
also applicable, 
