According to Raschig[1] two competing reactions occur when ammonia is in excess.
| (1) | NH2Cl + NH3 = N2H4HCl hydrazine hydrochloride | |
| and | (2) | 3NH2Cl + 2NH3 = N2 + 3NH4Cl. |
When the excess of ammonia is large, as on the addition of ammonia fort, the second reaction predominates and the yield of nitrogen gas is almost quantitatively proportional to the quantity of available chlorine present. As ammonium chloride has no germicidal action, and hydrazine a carbolic coefficient of only 0.24 (Rideal), the formation of these compounds should be avoided.
The dosage of chloramine can be checked by titration of the available chlorine (see [p. 82]) immediately after treatment or by the estimation of the increment in the total ammonia (free and albuminoid). Routine determinations of the latter made in Ottawa show that practically the whole (90-95 per cent) of the added ammonia can be recovered by distillation with alkaline permanganate and that 85-90 per cent is in the “free” condition.
In operating the chloramine process it is important that the pipes used for conveying the chloramine solution should be of ample dimensions and provided with facilities for blowing out the lime that deposits from the solution.
Ca(OCl)2 + 2NH3 = 2NH2Cl + Ca(OH)2.
The marked activity of chloramine as a chlorinating agent could be predicated from its heat of formation, which is 8,230 calories. The other possible chloramines should be even more active as the heat of formation of these compounds are:
| Dichloramine | NHCl2 | — | 36,780 calories. |
| Nitrogen trichloride | NCl3 | — | 65,330 calories. |
Dichloramine is unknown but nitrogen chloride has been prepared and is a highly explosive yellow oil that decomposes slowly when kept under water in the ice box. NCl3 can be easily prepared by passing chlorine gas into a solution of ammonium chloride and this process would suggest that a method might be found of utilising chlorine and ammonia as gases for the production of nitrogen trichloride as a germicide for water chlorination. NH4Cl + 3Cl2 = NCl3 + 4HCl.
The “available” chlorine content of the chloramines is double the actual chlorine content as each atom of chlorine will liberate two atoms of iodine from hydriodic acid.