ON THE AIR AND WATER OF TOWNS. 23 
and soil where there is also little flow of water. It might however be viewed 
_as an oxidation, with excess of oxygen also where the large extent of surface 
presented by the porous materials gives an increased facility for oxidation, 
‘or rather presents compressed oxygen, so as to be more effective. 
_ It will be of interest to know what becomes. of the carbon and hydrogen 
‘in these cases, if they are removed together. These nitrates do not occur 
toany extent in purifying large bodies of water, nor do they occur in 
filtering through rocks or sand as in nature, but they occur in more close 
situations, under streets and houses and in undrained ground, according as 
it is saturated with animal matter. It is found in sewer water, in the Thames 
_ water, and in all dirty streams into which sewers empty themselves: perhaps 
the reason of its not being found in larger quantities in streams from drained 
land is simply the want of animal matter, or it may not be formed more 
rapidly than the plants can use. It is found however in wells which are 
_ situated in well-manured gardens, and in all wells at the backs of houses, 
without any exception, yet met with by me. 
The wells of private houses, and we may say wells generally, are placed 
in that spot which of all others is the worst, the cesspools and the wells 
_ always too near, generally close to each other. I was first led to examine 
_ this from a complaint made in Manchester, where a case of this kind fur- 
_ nished water of an oily appearance, containing about 90 grains of matter in 
a gallon, and being excessively disagreeable. The same well was examined 
_ in summer, and the matter had risen up to nearly an ounce in a gallon. The 
_ well was of course not ft for use in this state. 
_ Inthe same neighbourhood was a churchyard, and around it I examined 
_ five wells, one of them especially, sufficiently far removed from cesspools to 
_ make me believe that the churchyard was the only cause of the impurity. 
The wells of London al! contain nitric acid to a certain extent, but they vary 
exceedingly in the amount. The following have only a small quantity :—Ex- 
change, Rood Lane, Eastcheap, St. Paul’s Churchyard, Tower Hill, Covent 
Garden, Lincoln’s-Inn Court, St. Clement’s, Strand, Aldgate Pump, and Bow 
Church. It seemed to me from the situation of the old well at Clerkenwell, 
that it was very well fitted for obtaining nitrates, and on examination it was 
found to be exceedingly well-filled with earthy salts, containing 148 grains 
of solid matter to the gallon, of which several were nitrate of lime. The 
3 water of this neighbourhood would contain about 20 grains to the gallon in 
_ a natural state, if we may judge from the water generally found in the valley 
of the Thames. 
_ Another well in North Street, Tottenham Court Road, was examined, as 
_ from the state of the drainage I expected it to contain a considerable quan- 
tity of earthy salts. Here also I was not deceived, having got 130 grains of 
alphates, chlorides and nitrates in a gallon; the water itself a fluid which I 
_ There is then a constant formation of nitric acid under towns. It is a 
little surprising that organic matter, properly so called, should not be found 
‘in those wells; the nearest to a source of organic matter do actually con- 
tain the least, because in these cases it is more readily converted into 
hitric acid, which may very properly be called here oxidized organic matter. 
At the same time also it must be remembered, that the nitrates decompose 
“ar y organic matter present if heat be applied, so that no blackening of the 
ea can be perceived. Those wells of London first mentioned do not 
_ eontain much of these salts, but sufficient to deprive them of organic matter, 
