A PRIZE ESSAY. 
51 
we take away. First, wc take away all the acids 
except the phosphoric. Secondly, we take away 
nearly all the potash and soda. What is left ? All 
the other bases and phosphoric acid. It is evident, 
therefore, that the strength of ashes can never be 
wholly leached out, if that depends upon the salts. 
In spent ashes, we have nearly all the bonedust left; 
and, besides this, a portion of what is usually consid¬ 
ered the real strength, that is, the potash. This is 
chemically united to certain of the other constituents 
of ashes. You cannot leach it out, leach you ever so 
long. Upset your leach tubs, shovel over your spent 
ashes, mix it up with fermenting manure, where a 
plenty of fixed air is given off. Here is the secret of 
the value of spent ashes, so far as the potash or ley 
strength is concerned. This exposure to air, to car¬ 
bonic acid, lets loose the potash, which was chemically 
combined with the other matters. Water would 
never have done this. Mark now a practical lesson, 
taught here by chemistry, and confirmed by experi¬ 
ence. Leached ashes must never be used on wet soil, 
if we want its alkali to act. The close wet soil, per¬ 
haps even half covered at times with water, excludes 
the air. The carbonic acid of air, that which alone 
extracts the alkali from spent ashes, cannot here act. 
There is this other lesson to be learned from, these 
facts, that it is chiefly the alkaline action which is 
wanted from spent ashes. Hence no one who thus 
understands the source, and the true value of ashes, 
will allow the alkaline portion to be first leached out, 
unless he can find a more economical use for it than 
its application as a fertilizer. Perhaps no fact speaks 
louder, that the great action of spent ashes is that of 
its potash, than this, that where we prevent that from 
being extracted, the spent ashes are of little value. 
If, then, spent ashes derive their great value from the 
potash, much more will unleached ashes derive their 
value from their potash. 
Now, reader the point to which I have led you, 
