The shape of the curve obtained with a colour of 40 p.p.m. somewhat resembled that of a mono-molecular reaction and the results were calculated accordingly. The mathematical expression of this law is _dN_/_dt_ = _KN_ where _N_ is the concentration of the available chlorine in parts per million. Integrating between _t__{1} and _t__{2} the formula _K_ = log(_N__{1}/_N__{2})/(_t__{2} - _t__{1}) is obtained. If the compound absorbing the chlorine were simple in character, and the chlorine were present in large excess, the value of _K_ would be constant. In the experiments recorded, _K_ constantly decreases, due to the decreasing concentrations of the reacting substances and the complex nature of the organic matter. The results show the effect of organic matter on the reduction of the chlorine concentration available for germicidal action and also the importance of avoiding a local excess of chlorine (_vide_ p. 41). An effort has been made by some observers to find a quantitative relation between the organic matter, expressed as oxygen absorbed in parts per million, and the chlorine required for oxidation, but without definite result. Some of the results obtained are given in Table VII. TABLE VII.--OXYGEN TO CHLORINE RATIO -------------------------+------------------------- | Oxygen Absorbed Observer. | Ratio -----------------. | Chlorine Absorbed -------------------------+------------------------- Rouquette | 1 Bonjean | 0.5 Orticoni | Less than 1 Valeski and Elmanovitsch | 0.4 Race | 0.4 Theoretical | 0.22 -------------------------+------------------------- The value of 0.4 (0.39) obtained by the author is the average of over one hundred determinations covering a period of two years. The experiments of Zaleski and Elmanovitsch were made with the water of the Neva River. The divergence in the ratios affords additional evidence in favor of reaction (2) mentioned on page 28 and also shows that the chlorinated compounds are less readily oxidized than those from which they are produced. Heise[8] has found that the amount of chlorine consumed is usually proportional to the concentration in which it is added though not necessarily a function of the concentration of the organic matter. =Temperature.= The evidence regarding the effect of temperature upon the dosage required is somewhat conflicting. Ellms (_vide supra_) found that the velocity of the germicidal action varied directly with the temperature and this has also been the author's experience with laboratory experiments. Typical examples of these are given in Tables VIII and IX. TABLE VIII.[A]--EFFECT OF TEMPERATURE AVAILABLE CHLORINE 0.4 PART PER MILLION