When chlorine gas was treated with a 0.5 per cent solution of ammonia in the proportion of 1 molecule of chlorine to 1.90-1.95 molecules of ammonia, Noyes and Lyon[8] found that nitrogen and nitrogen-trichloride were formed in equimolar quantities.

12NH3 + 6Cl2 = N2 + NCl3 + 9NH4Cl.

Bray and Dowell[9] showed that this reaction depended upon the hydrogen ion concentration and proceeded in accordance with the following equations:

(i).Acid solution 4NH3 + 3Cl2 = NCl3 + 3NH4Cl
(ii).Alkaline solution 8NH3 + 3Cl2 = N2 + 6NH4Cl.

In (i) with a ratio of chlorine to ammonia of 3 : 1 by weight, one-half of the chlorine is lost as ammonium chloride and one-half forms nitrogen trichloride, concerning which comparatively little is known; in (ii) the whole of the chlorine forms ammonium chloride, which has no germicidal value.

The effect of ammonia on the germicidal action of a solution of chlorine gas is shown in the [Table IV].

TABLE IV.[D]—EFFECT OF AMMONIA ON
CHLORINE GAS SOLUTION

Conditions. Colour of water 40 p.p.m. Turbidity, 5 p.p.m.
Contact
Period.		Available Chlorine 0.20 p.p.m., Ammonia.
Parts Per Million.
Nil.0.050.100.20
Nil.130.........
10mins.135140130135
1hour130130128120
4hours120112110105
24hours120145160170
[D] Resultsare B. coli per 10 c.cms.

Even when the ratio of Cl : NH3 was 4 : 1 by weight, practically the same as was used in the experiments of Noyes and Lyon, and Bray and Dowell, quoted above, the germicidal action was totally destroyed and the 24-hour results showed aftergrowths which were somewhat proportional to the amount of ammonia added. This was probably due to the formation of ammonium chloride, which provided additional nutriment for the organisms.