and the Constituents of Well- and River-waters. 207 
cannot be separated by filtration, are of two classes: one non- 
nitrogenous, the other nitrogenous. The former consist of car- 
bon, oxygen and hydrogen, and in the natural progress of decay 
are resolved into carbonic acid and water; the other class con- 
tains in addition, nitrogen, sulphur and phosphorus. These 
elements unite in progress of time with hydrogen, and form 
ammonia, sulphuretted hydrogen and phosphuretted hydrogen. The 
ammonia, which is always formed in considerable quantity, is 
ultimately resolyed by combination with oxygen into nitrous acid 
and water, according to the following equation :— 
NH?+60=NO0?+3H0. 
If Thames water, which, as is well known, contains a large 
quantity of nitrogenous organic matter, be allowed to remain for 
some time exposed to the air in an open vessel, the nitrogen of 
the organic matter will unite first with hydrogen to form am- 
monia ; and this base may be readily detected by slightly acidula- 
ting the water with hydrochloric acid, evaporating to dryness on 
a water-bath, and testing the residue with potash. In progress 
of time, however, a portion of the ammonia is resolved, accord- 
ing to the above equation, into nitrous acid, which unites 
with an equivalent of ammonia, and may be found in the water 
as nitrite of ammonia. If to a portion of Thames water which 
has been exposed for some time to the atmosphere, a little pure 
potash is added and the water is then evaporated to dryness, 
abundance of nitrous acid may be found in the residue by first 
placing it in a flask, adding dilute sulphuric acid, and placing 
in the neck of the flask a slip of paper moistened with acidulated 
starch-paste and iodide of potassium. In a few seconds the 
paper will become intensely lve. In warm weather this change 
takes place in a few days, and may be effected almost instan- 
taneously by application of heat. 
When Thames water is distilled, the complicated organic sub- 
stances contained in it are speedily resolved into more simple 
compounds, and amongst these ammonia and nitrous acid occupy 
a prominent position. On testing the first portions of water 
distilled from a 20-gallon still, it was found to be decidedly acid 
to test-paper. Two gallons of this water were neutralized with 
pure alcoholic potash, evaporated to dryness, and the residue 
tested for nitrous acid; the paper became blue instantly. To 
another two gallons of the same distilled water, acid to test-paper, 
was added a few drops of hydrochloric acid, and the water eva- 
porated to dryness on a water-bath. On testing the residue 
with pure potash, abundance of ammonia was evolved. The ex- 
periment was repeated on the first four gallons of water distilled 
from six separate twenty gallons of Thames water, with the same 
