[A] Corrected for the alkali produced by HClO + 2KI = KCl + KOH + I_{2}. Although every precaution was taken to exclude carbonic acid, a portion of the hydrolysis was probably due to this acid, which would remove calcium hydrate from the sphere of action and consequently alter the equilibrium. The above figures are only applicable to the particular sample used; other samples containing different excesses of base would yield different hydrolytic values. The results are in agreement with the hypothesis presented and confirm the theoretical deduction that very dilute bleach solutions are completely hydrolysed if no salts are present that will dissociate and increase the OH' concentration. Hydrolysis is reduced by caustic alkalies and alkaline carbonates, and increased by acids and acid carbonates that reduce the OH' concentration. The effect of chlorides is anomalous and no adequate explanation for their action can be given at present. The addition of small quantities of sodium chloride (0.1 per cent) increases the hydrolysis of bleach solutions but much larger quantities tend to the opposite direction. The effect of these substances upon the velocity of the germicidal action of bleach solutions is in the same direction as the hydrolysing effect.[4] Sodium chloride in quantities up to 10 parts per million has a very limited effect but larger quantities (90 p.p.m.) increase the velocity of the reaction. Sodium chloride, in the absence of hypochlorites, was found to have no influence upon the viability of _B. coli_ in water. In quantities up to approximately 5 p.p.m., sodium hydroxide has but little influence; 5-10 p.p.m. reduce the velocity to a marked degree, but when the quantity of caustic is still further increased the germicidal action of the alkali commences to be appreciable and may nullify the retarding action on the hypochlorite. Normal carbonates tend to reduce the velocity of the germicidal action and bicarbonates to increase it. Sulphuric acid, even in very small quantities (5 p.p.m.), has a marked accelerating effect and the total effect produced is much greater than can be accounted for by the germicidal activity of the acid alone. Weak acids such as carbonic acid and acetic acid are also effective accelerators. In one experiment a 0.01 per cent solution of bleach was found to be 40 per cent hydrolysed. By passing carbonic acid gas this was increased to 95 per cent and the velocity of the germicidal action of this solution was found to be approximately 100 per cent greater than that of the uncarbonated one. Norton and Hsu[5] have shown that the germicidal activity of some disinfectants is a function of the hydrogen ion concentration, but this factor is insufficient to account for the effect of acids on bleach solutions.