A PRIZE ESSAY. 
43 
assuredly burn your crop, as the puddle formed by a 
cow burns the grass upon which she empties her 
watering pot. Here the urine, forming caustic am¬ 
monia, acts as would caustic potash, or a lump of stone 
lime, left to slack upon the grass. You want to 
change this burning or caustic ammonia into mild am¬ 
monia, or to combine it with some substance which 
has not only that effect, but also keeps it from flying 
away. Unless you understand, then, the principles 
of these actions, and apply them too, your labor is all 
vanity, when you attempt to save your own or your 
cattle’s urine. 
These principles are in number, two. First, the 
principle which changes caustic to mild ammonia is 
carbonic acid, derived from air, or decomposing mould. 
Second, the principles which render ammonia less 
volatile, or wholly fixed, are certain acids, formed in 
mould, as sour mould, or certain salts which give up 
their acid to the ammonia. Plaster of Paris does this, 
by changing its lime for ammonia. Now let us go 
into the reason of this a little, and see if we can un¬ 
derstand it. Very slowly, and supposing moisture 
present, the oil of vitriol of the plaster quits its lime, 
and unites to the ammonia, and so changes a volatile 
into a fixed salt. Now this is a change which has 
been of late much insisted on, and the practice recom¬ 
mended, of strewing the stable and barn cellars, and 
even the privies, with plaster, to save the ammonia, 
which escapes in these places. But it is doubtful 
whether the saving is as great as is usually supposed, 
for the ammonia arising from the urine is caustic, it 
flies off as caustic ammonia, that has no effect upon 
plaster. To produce this mutual effect of ammonia 
and plaster, the caustic ammonia must previously have 
been made mild. However, this plan is applicable 
only on a small scale. Copperas, alum, common salt, 
potashes, and wood ashes, all act.to fix the volatile 
ammonia, and have all been recommended for this 
purpose. But it is easily seen, that, in employing 
