The relation between the time of reduction at 20° C. and that at 37° C.
is approximately two to one, but if an observer incubates at 37° C. he
should work out his own comparative 37° C. table or factor.
A relative stability of 75 signifies that the sample examined contains a
supply of available oxygen equal to 75 per cent of the amount of oxygen
which it requires in order to become perfectly stable. The available
oxygen is approximately equivalent to the dissolved oxygen plus the
available oxygen of nitrate and nitrite. Nitrite in sewage is usually so
low as to be negligible.