resulting
in the production of nitrites. The nitrifying organisms first produce
nitrous acid products (nitrites), and in the further development of the
nitrifying process these are changed to nitrates. The ammonia formed as
the result of the decomposition of nitrogenous organic matter readily
undergoes nitrification changes. Nitrates and nitrites alone are not
injurious in water, but they are usually associated with objectionable
bacteria and generally indicate previous contamination.[90]

267. Interpretation of a Water Analysis.--"Total solid matter"
represents all the mineral, vegetable, and animal matter which a water
contains. It is the residue obtained by evaporating the water to dryness
at a temperature of 212 deg. F. Average drinking water contains from 20 to
90 grains per gallon of solid matter. "Free ammonia" is that formed as a
result of the decomposition of animal or vegetable matter containing
nitrogen. Water of high purity usually contains less than 0.07 parts
per million of free ammonia. "Albuminoid ammonia" is derived from the
partially decomposed animal or vegetable material in water. The greater
the amount of nitrogenous organic impurities, the higher the albuminoid
ammonia. A good drinking water ought not to contain more than 0.10 part
per million of albuminoid ammonia. An abnormal quantity of chlorine
indicates surface drainage or sewage contamination, or an excess of
alkaline matter, as common salt. Nitrites should not be present, as they
are generally associated with matter not completely oxidized. Nitrites
are usually considered more objectionable than nitrates; both are
innocuous unless associated with disease-producing nitrooerganisms.

268. Natural Purification of Water.--River waters are sometimes dark
colored because of large amounts of dissolved organic matter, but in
contact with the sun and air they gradually undergo natural purification
and the organic matter is oxidized. However, absolute reliance cannot be
placed upon natural purification of a bad water, as the objectionable
organisms often have great resistive power. There is no perfectly pure
water except that prepared in the chemical laboratory by distillation.
All natural waters come in contact with the soil and air, and
necessarily contain impurities proportional to the extent of their
contamination.

269. Water in Relation to Health.--There are many diseases, of which
typhoid fever is a type, that are distinctly water-born. The t