A PRIZE ESSAY. 
47 
We have said so much, upon the action of ammonia 
and nitrogen, that you will perceive how important a 
part nitre is likely to play in manure. Not only does 
the nitrogen act here, but the oxygen, the other com¬ 
ponent of the acid, also acts. It acts upon the mould 
as air itself would. Besides, the mould of soil and 
manure imbibes and condenses this oxygen in its 
pores, and consequently heats a little; so that saltpe¬ 
tre. whether added as such to soil, or formed in ma¬ 
nure, as it is always, helps to warm a little the soil, 
like fermenting manure. So far as these effects are 
desirable they may be expected from the use of salt¬ 
petre. But this, reader, if you buy your saltpetre, is 
procuring a small effect at a great price. The action 
of the alkali of saltpetre is not different from alkali in 
other shapes, and therefore if you have money to lay 
out for salts, let me advise you, reader, to spend it 
rather for ashes than for saltpetre. 
SECTION XI. 
OF ARTIFICIAL EITRB BEDS. 
But there is a fashion in manures as well as in other 
things, and saltpetre is now so fashionable that you 
may be inclined to use it. Be it so. I will show you, 
reader, how to make it for yourself, and at the same 
time form a large pile of capital mould. But as you 
have begun to inquire a little into the reason of things, 
let us go a little into the reasons why the earth under 
all barns where cattle are kept, why the plaster of old 
houses and cellar walls, always afford saltpetre. You 
well know that this is the case, and why ? We have 
already told you, that the acid of saltpetre, that is, the 
aqua-fortis, is formed of the air we breathe. Now 
