MODUS OPERANDI
Before considering the "modus operandi" of chlorine and hypochlorites,
it will be advisable to take up the composition of the latter substances
and particularly that of "bleach." Bleach is manufactured by passing
chlorine gas over slaked lime and the ensuing reactions are often
represented by the equation Ca(OH)_{2} + Cl_{2} = CaOCl_{2} + H_{2}O.
This represents the substance formed as a pure oxychloride of calcium
which contains approximately 50 per cent of chlorine, but the article
commercially produced never contains this amount of chlorine, the usual
percentage being from 35-37. The general composition of commercial
bleach is fairly uniform. This is shown in the following analyses of
which two are of German bleach examined by Lunge and one of Canadian
manufacture analysed by the author.
-------------------------------+----------------+--------
| Lunge. | Race.
-------------------------------+--------+-------+--------
| % | % | %
Available chlorine | 37.00 | 38.30 | 37.50
Chlorine as chlorides | 0.35 | 0.59 | 0.52
Chlorine as chlorates | 0.25 | 0.08 | 0.18
Lime | 44.49 | 43.34 | 44.12
Magnesia | 0.40 | 0.31 | 1.28
Iron oxide | 0.05 | 0.04 | 0.11
Alumina | 0.43 | 0.41 | 0.46
Carbon dioxide | 0.18 | 0.31 | 0.22
Silica | 0.40 | 0.30 | 0.52
Water and undetermined | 16.45 | 16.32 | 15.09
-------------------------------+--------+-------+--------
From these analyses the constitutional of commercial bleach might be
represented by the formula
4CaOCl_{2}.2Ca(OH)_{2}.5H_{2}O
which assumes it to contain:
68.0 per cent of calcium hypochlorite,
20.0 per cent of calcium hydroxide,
and 12.0 per cent of water.
In this formula calcium hypochlorite has been written CaOCl_{2}, but
this substance actually contains one atom of oxygen less than the true
hypochlorite, which has the constitutional formula ClO-Ca-OCl. This
difference led some of the earlier chemists to regard CaOCl_{2} as a
mixture of equal molecules of calcium chloride and calcium hypochlorite
(CaCl_{2} + Ca(OCl)_{2} = 2CaOCl_{2}), but it has been definitely
established that no calcium chloride exists in the free state in dry
commercial bleach.
Since the very earliest days when the process of bleaching was
investigated it was considered to be a process of oxidation and it is
not surprising that Lavoisier and his pupils, who had noted the strong
decolourising action of the gas discovered previously by Scheele, should
regard it as a compound that contained oxygen. They were confirmed in
this view by the fact that an aqueous solution of the gas slowly evolved
oxygen when placed in bright sunlight, and lost its bleaching
properties. Watt disproved this and showed that the evolution of oxygen
was due to the action of the chlorine on water.
Cl_{2} + H_{2}O = 2HCl + O.
The bleaching action was not due to the chlorine "per se" but to the
nascent oxygen produced in the presence of moisture. Later, when bleach
and other chlorine compounds came into use as deodourisers, their action
was attributed to the oxygen produced and when their germicidal
properties became known it was natural to assume that the destruction of
bacteria was due to the same cause. Some of the earlier experimental
work supported this view. Fischer and Proskauer[1] found that humidity
played an important part in chlorine disinfection, probably because it
favoured oxidation. In air saturated with moisture micro-organisms were
killed by 0.3 per cent of chlorine in three hours but when the air was
dry practically no action occurred. They concluded that chlorine was not
directly toxic. Warouzoff, Winogradoff, and Kolessnikoff[2] were unable
to confirm the results of Fischer and Proskauer and found that a mixture
of chlorine gas and air killed tetanus spores in one minute.
The nascent oxygen hypothesis was clearly and succinctly expressed by
Prof. Leal during the hearing of the Boonton, N. J., case and the
following abstracts have been taken from his evidence:
"... That on the addition of bleach to water the loosely formed
combination forming the bleach splits up into chloride of calcium and
hypochlorite of calcium. The chloride of calcium being inert, the
hypochlorite acted upon by the carbonic acid in the water either free or
half bound, splits up into carbonate of calcium and hypochlorous acid.
The hypochlorous acid in the presence of oxidisable matter gives off its
oxygen; hydrochloric acid being left. The hydrochloric acid then drives
off the weaker carbonic acid and unites with the calcium forming
chloride of calcium.
"That the process was wholly an oxidising one, the work being done
entirely by the oxygen set free from the hypochlorous acids in the
presence of oxidizable matter....
"We have used during our investigations, the term 'potential oxygen' as
expressing its factor of power. When set free, it is really nascent or
atomic oxygen and is, in its most active state, entirely different from
the oxygen normally in water...."
The reactions suggested are expressed in the following equations:
(i). 2CaOCl_{2} = CaCl_{2} + Ca(OCl)_{2}
(ii). Ca(OCl)_{2} + CO_{2} + H_{2}O = CaCO_{3} + 2HClO
(iii). 2HClO = 2HCl + O_{2}
(iv). CaCO_{3} + 2HCl = CaCl_{2} + CO_{2} + H_{2}O.
Phelps, during the hearing of this case, suggested that hypochlorites
were directly toxic to micro-organisms but this view was not supported
by any definite evidence and the nascent oxygen hypothesis met with
almost universal acceptance. Investigations made by the author in 1915,
1916 and 1917 have produced data which cannot be adequately explained by
the nascent oxygen hypothesis.[3]
The disinfecting action of bleach can be most conveniently considered by
regarding it as a heterogeneous mixture of the reactants and resultants
of the reaction
CaO + H_{2}O + Cl_{2} <=> CaOCl_{2} + H_{2}O
which is in equilibrium for the temperature and pressure obtaining
during the process of manufacture. Under suitable physical conditions
the chlorine content can be increased to 40-42 per cent but such a
product is not so stable as those represented by the analyses on page 14
and which contain approximately 20 per cent of excess hydrate of lime.
The stability of bleach depends upon this excess of base (Griffen and
Hedallen[4]) and although magnesia can be partially substituted for this
excess of lime, a minimum of 5 per cent of free hydrate of lime is
required to ensure stability.
On dissolving bleach in water the first action is the decomposition of
calcium oxychloride into an equal number of molecules of calcium
hypochlorite and calcium chloride.
2CaOCl_{2} = Ca(OCl)_{2} + CaCl_{2}.
In dilute solution these salts are dissociated and hydrolysis tends to
occur in accordance with the equations
2Ca(OCl)_{2} + 4H_{2}O <=> 2Ca(OH)_{2} + HOCl + HCl and
CaCl_{2} + 2H_{2}O <=> Ca(OH)_{2} + 2HCl.
Calcium hydrate and hydrochloric acid are both practically completely
dissociated, i.e. there is a large and equal quantity of H^{.} and OH',
and the product is much greater than K_{_w_} (ionic product of water),
and hence there is a combination of these ions, leaving the solution
neutral and no undissociated acid or base exists. This statement is only
approximately correct as hydrochloric acid is slightly more dissociated
than calcium hydroxide (ratio 9:8) and the solution is consequently
slightly acid, i.e. the H^{.} concentration is greater than 1 x 10^{-7}.
Hypochlorous acid is only very slightly dissociated, especially in the
presence of the OCl' ion due to the dissociation of the Ca(OCl)_{2}, as
compared with Ca(OH)_{2} and hydrolysis of the Ca(OCl)_{2} proceeds with
increased dilution. The action is best represented by the equation
2Ca(OCl)_{2} + 2H_{2}O <=> CaCl_{2} + Ca(OH)_{2} + 2HOCl
The hydrolytic constant of hypochlorous acid has apparently not been
determined but as the acid is weaker than carbonic acid, which has a
hydrolytic constant of 1 x 10^{-4}, the value is probably between 1 x
10^{-3} and 1 x 10^{-4}. From the formula _x_^{2}/(1 - _x_)_v_ =
_k__{_wv_} in which 1 mole of pure Ca(OCl)_{2} is dissolved in _v_
litres, _x_ is the fraction hydrolysed, and _k__{_wv_} is the hydrolytic
constant, complete hydrolysis occurs (_x_ = 1) when _v_ is not greater
than 1 x 10^{4} litres. This is equivalent to a concentration of not
less than 7.1 p.p.m. of available chlorine. Solutions of pure
hypochlorites are alkaline in reaction because of the excess of hydroxyl
ions (minimum concentration 1 x 10^{-4}). In solutions of bleach the
hydrolytic action is retarded by the OH' due to the free base, and
accelerated by the excess of H^{.} caused by the dissociation and
partial hydrolysis of CaCl_{2}; the final result is determined by the
relative proportions and the effect of the free base usually
preponderates. The addition of any substance that reduces the OH'
concentration enables hydrolysis to proceed to completion and affords a
rational explanation of the fact that solutions of bleach, on
distillation with such weak acids as boric acid, yield a solution of
hypochlorous acid. It also explains why the addition of an acid is
necessary in Bunsen's method (_vide_ p. 79) of analysing hypochlorite
solutions. It has been stated that when hydrochloric acid is employed
the increase in the oxidising power is due to the action of the acid
upon calcium chloride but this never occurs under ordinary conditions;
weak acids such as carbonic or acetic will give practically the same
result as hydrochloric acid in solutions of bleach of the strength used
in water treatment. The slightly higher result obtained with strong
acids is due to the decomposition of chlorates.
The effect of dilution alone is shown by the data given below. A 2 per
cent bleach solution, containing very little excess base, was diluted
with distilled water and the various dilutions titrated with
thiosulphate after the addition of potassium iodide. In one series the
solutions were titrated directly, and after acidification in the other.
The results[A] were as follows:
HYDROLYSIS OF BLEACH SOLUTION
-----------------------------------+-----------------------
Strength of Solution. Grams Bleach | Direct Titration x 100
Per 100 c.cms. | --------------------.
| Acid Titration
-----------------------------------+-----------------------
2.0 | 30.8
0.2 | 34.3
0.1 | 41.8
0.02 | 67.5
0.002 | 100.0
-----------------------------------+-----------------------
[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.
The effect of sodium chloride on the bacteriological results, like that
on the hydrolytic constant, is anomalous. Similar effects have been
observed on the addition of this salt to phenol and other disinfectants.
The _raison d'etre_ of the increased activity is obscure but it is
possible that the salt renders the organisms more susceptible to the
action of the germicide.
Ammonia, though decreasing the hydrogen ion concentration of bleach and
other hypochlorite solutions, markedly increases the velocity of the
reaction; chlorinated derivatives of ammonia (chloramines), which have a
specific germicidal action, are formed. These will be discussed at
length in Chapter IX, p. 115.
Rideal[6] has shown that the addition of ammonia to sodium hypochlorite
destroys the bleaching activity in acid solution. This has been found by
the author to be also true for calcium hypochlorite (bleach). If the
bleaching effect is due to oxidation, the oxidising power of
hypochlorites must be considered to be destroyed by the addition of
ammonia. The property of oxidising organic matter in water is also
destroyed; this is well illustrated in Table II which shows the rate of
absorption of chlorine and chloramine by the Ottawa River water. The
water used in this experiment contained 40 p.p.m. of colour and absorbed
9.5 p.p.m. of oxygen (30 mins. at 100 deg. C.).
TABLE II.[A]
------------------+-------------------------------------------------
| ABSORPTION OF AVAILABLE CHLORINE AT 63 deg. F.
Time of Contact +----------------------+--------------------------
Minutes. | Chlorine as Bleach. | Chlorine as Chloramine.
------------------+----------------------+--------------------------
Nil. | 10.00 | 9.98
5 | 6.50 | 9.98
10 | 5.91 | 9.90
20 | 5.18 | 9.90
40 | 4.47 | 9.84
60 | 3.90 | 9.84
80 | 3.65 | 9.84
20 hours | .... | 9.68
------------------+----------------------+--------------------------
[A] Results are parts per million.
From a consideration of these and other experiments made by the author
in January, 1916, it became apparent that the nascent oxygen hypothesis
entirely failed to explain the results obtained, and that they must be
attributed to a direct toxic action of the chlorine or chloramine.
Dakin et al.[7] arrived at a similar conclusion from a consideration of
the results obtained during the use of hypochlorite solutions in the
treatment of wounds by Carrel's method of irrigation. They attributed
the marked beneficial action to the formation of chloramines _in situ_
by the action of hypochlorous acid upon amino acids and proteid bodies.
Compound chloramines (chlorinated aminobenzoic acids) were prepared in
the laboratory and found to give excellent results in reducing wound
infection. Later, other compounds were prepared for the purpose of
sterilising small quantities of water for the use of mobile troops (see
p. 128).
Rideal[6] was the first to note the strong germicidal power of
chloramine and attributed the persistent germicidal activity of
hypochlorites in sewage to the formation of chloramine and chloramine
derivatives.
Further evidence against the nascent oxygen theory of chlorine
disinfection is to be found in the fact that such active oxidising
agents as sodium, potassium, and hydrogen peroxides have a much lower
germicidal activity than chlorine when compared on the basis of their
oxygen equivalents. Table III shows chlorine to be approximately five
times as active as potassium permanganate when compared on this basis.
TABLE III.[A]--COMPARISON OF BLEACH AND POTASSIUM PERMANGANATE
-----------+------------------+-------------------
| BLEACH |
|Available Chlorine| POTASSIUM
Contact | 0.35 p.p.m. | PERMANGANATE.
Period. +------------------+-------------------
|Oxygen Equivalent. Parts Per Million.
+--------+---------+---------+---------
| 0.08 | 0.133 | 0.266 | 0.400
-----------+--------+---------+---------+---------
Nil | 140 | ... | ... | ...
30 mins | 90 | 122 | 115 | 110
1 hour | 68 | 115 | 100 | 80
1-1/2 hours| 63 | 108 | 95 | 75
4 hours | 50 | 95 | 80 | 50
-----------+--------+---------+---------+---------
[A] Results are _B. coli_ per 10 c.cms.
The germicidal activity of oxidising agents has been shown by Novey and
others to be somewhat proportional to the energy liberated during the
reaction but even when this factor is taken into consideration chlorine
compounds are more active than other oxidising agents. Hypochlorous acid
is far superior to hydrogen peroxide as a germicidal agent and is as
active as ozone, which liberates a greater amount of energy.
2HClO = 2HCl + O_{2} + 18,770 calories
2H_{2}O_{2} = 2H_{2}O + O_{2} + 46,120 calories
2O_{3} = 3O_{2} + 60,000 calories.
Again, solutions of chlorine gas and hypochlorites having the same
oxidising activity, as determined by titration with thiosulphate after
the addition of potassium iodide and acid, i.e. contain equal amounts of
available chlorine, show approximately the same germicidal activity in
water. On the addition of ammonia, the hypochlorite solutions retain
their ability to liberate iodine from potassium iodide (Wagner test) but
the property of oxidising such dyestuffs as indigo is destroyed and the
germicidal activity is increased. Ammonia, when added to solutions of
chlorine gas, diminishes the property of liberating iodine from
potassium iodide, the bleaching effect on dyestuffs, and the germicidal
action. It is often assumed that chlorine forms hypochlorous acid on
solution in water Cl_{2} + H_{2}O = HClO + HCl but the results obtained
on the addition of ammonia indicate that either very little hypochlorous
acid is formed or that ammonia and hypochlorous acid do not form
chloramine in the presence of hydrochloric acid.
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.
12NH_{3} + 6Cl_{2} = N_{2} + NCl_{3} + 9NH_{4}Cl.
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 4NH_{3} + 3Cl_{2} = NCl_{3} + 3NH_{4}Cl
(ii). Alkaline solution 8NH_{3} + 3Cl_{2} = N_{2} + 6NH_{4}Cl.
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.[A]--EFFECT OF AMMONIA ON CHLORINE GAS SOLUTION
_Conditions._ Colour of water 40 p.p.m. Turbidity, 5 p.p.m.
---------+----------------------------------------
|Available Chlorine 0.20 p.p.m., Ammonia.
Contact | Parts Per Million.
Period. +---------+---------+----------+---------
| Nil. | 0.05 | 0.10 | 0.20
---------+---------+---------+----------+---------
Nil. | 130 | ... | ... | ...
10 mins. | 135 | 140 | 130 | 135
1 hour | 130 | 130 | 128 | 120
4 hours | 120 | 112 | 110 | 105
24 hours | 120 | 145 | 160 | 170
---------+---------+---------+----------+---------
[A] Results are _B. coli_ per 10 c.cms.
Even when the ratio of Cl:NH_{3} 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.
It has often been assumed that hypochlorite solutions are decomposed on
addition to water containing free or half-bound carbonic acid with the
production of free chlorine, but no evidence has been adduced in
support. Free chlorine can be separated from hypochlorous acid in
aqueous solution by extraction with carbon tetrachloride and when this
solvent is shaken with a carbonated hypochlorite solution it is found
that only traces of chlorine are removed.
Hypochlorous acid reacts with hydrochloric acid with the evolution of
free chlorine HClO + HCl = Cl_{2} + H_{2}O but in very dilute solution
the amount of free chlorine formed is exceedingly minute. Jakowkin[10]
has shown that this reaction does not proceed to completion and that the
concentration of free chlorine can be calculated from the equation HClO
x H^{.} x Cl' = 320Cl_{2} in which the reactions are expressed in gram
molecules per litre. The hydrogen ions and chlorine ions are obtained
from the dissociation of carbonic acid (H_{2}CO_{3} <=> H^{.} +
HCO_{3}') and chlorides (NaCl <=> Na^{.} + Cl') and also by the
dissociation of hydrochloric acid produced by the interaction of
hypochlorous acid and organic matter. HClO = O + HCl <=> H^{.} + Cl'. If
the formula of Jakowkin can be correctly applied to solutions containing
fractions of a part per million of hypochlorous acid the free chlorine
liberated by the addition of 1 p.p.m. of bleach to a water low in
chlorides would be of the order 10^{-7}-10^{-8} p.p.m.
_Sodium hypochlorite_ is probably hydrolysed in dilute solution in a
manner similar to that of bleach.
2NaOCl = NaCl + NaOH + HClO.
For solutions containing equal amounts of available chlorine,
electrolytic sodium hypochlorite is more dissociated than bleach because
of the absence of an excess of base, and this, together with the
presence of sodium chloride, accounts for the slightly higher germicidal
velocity obtained. The experience of pulp mills, with bleach and
electrolytic hypochlorites, confirms this: the latter is a much quicker
bleaching agent than bleach and it is often so rapid as to make it
desirable to reduce the velocity by the addition of soda ash.
Regarding hypochlorite solutions a phenomenon of more scientific
interest than of practical importance has been noted by Breteau[12] who
found that alkaline solutions of sodium hypochlorite containing 0.94 per
cent of available chlorine lost 3.6 per cent of their titer on dilution
with 80 volumes of water; also that this loss was increased by the
addition of small quantities of salt (sodium chloride) and more so by
carbonates and bicarbonates. The author has noted similar losses on
diluting bleach solutions and that the loss increased on standing. The
loss can be explained by the decomposition of hypochlorous acid, in the
presence of light, into hydrochloric acid and oxygen. 2HClO = 2HCl +
O_{2}
CHLORINE WATER. When a solution of chlorine in water is used as a
germicide the chemical reactions that occur differ materially from those
of hypochlorite solutions. On solution in water, hydration or solvation
probably takes place with the production of heat. Cl_{2}.Aq. = 2,600
calories. Chlorine water is comparatively stable but decomposes under
the influence of light in accordance with the equation Cl_{2} + H_{2}O =
2HCl + O; a similar reaction occurs in the presence of organic matter or
any substance capable of oxidation. Chlorine water contains only minute
traces of hypochlorous acid and there is no evidence that the
endothermic reaction
Cl_{2}.Aq + H_{2}O = HClO.Aq + HCl.Aq
-2600 - 68,460 = -29,930 - 39,315 - 1815
occurs in a measurable degree.
From thermochemical considerations hypochlorous acid and chlorine water
should be about equally active as oxidising agents.
2HClO.Aq = 2HCl + O_{2} + 18,770 calories
2Cl_{2}.Aq + 2H_{2}O = 2HCl + O_{2} + 15,340 calories
2Cl_{2}. + Aq + 2H_{2}O = 2HCl + O_{2} + 20,540 calories
When a solution of chlorine or hypochlorite is added to water as a
germicidal agent, a variety of reactions occur the character of which is
determined by the nature of the mineral and organic matter in the water
and the type of chlorine compound added. The general reactions are of
three types (1) oxidation of the organic matter, (2) direct chlorination
of the organic matter, and (3) a bactericidal action.
In the treatment of waters that contain appreciable amounts of organic
matter almost all the chlorine is consumed in reaction (1) and even with
filter effluents it is probably true that oxidation accounts for the
greater portion of the chlorine consumed. The author has found that a
dosage of 0.02 part per million of available chlorine was more effective
in destroying _B. coli_ in distilled water than 0.40 p.p.m. in a water
absorbing 9.5 p.p.m. of oxygen (30 mins. at 100 deg. C.).
Reaction (1) can be adequately explained by the nascent oxygen
hypothesis and it is this reaction that determines the dosage required
for effective sterilisation. (See Chap. III.)
Very little information is available regarding reaction (2) but there is
little doubt that a direct chlorination of the organic matter does occur
and it is more than probable that these chlorinated derivatives are
largely responsible for the obnoxious tastes and odours produced in some
waters. It has been suggested that these were due to the formation of
chloramines. This view was formerly supported by the author but the
chloramine treatment at Ottawa and other places has demonstrated the
inadequacy of this explanation. It is true that the odour of chloramine
is stronger and more pungent than that of chlorine, but chloramine in
the Ottawa supply, even with doses as high as 0.5 part per million of
available chlorine, has caused no complaints.
The odour of some of the organo-chloro compounds is more penetrating and
obnoxious than those of chlorine and chloramine, and it is quite
possible that some of the higher homologues of chloramine are in this
class. It should be noted, however, that some of the chloro-amido
compounds prepared by Dakin are white, odourless, crystalline
substances.
Practically nothing is known regarding the specific nature of the
mechanism involved in reaction (3). The hypothesis that chlorine, and
chlorine compounds, exert a direct toxic action on the micro-organisms
marks an advance in the science of water treatment but does not indicate
the physiological processes involved. Cross and Bevan[11] have shown
that chloro-amines have a tendency to combine with nitrogenous molecules
and to become fixed on cellulose; it is therefore possible that reaction
is a cytolytic one in which the chlorine attacks and partially or wholly
destroys the membranous envelope of the organisms. A portion of the
chlorine or chlorine-compound may also penetrate the membrane and
produce changes that result in the death of the organism.
BIBLIOGRAPHY
[1] Fischer and Proskauer, Rev. d'Hyg., 1884, 6, 515.
[2] Warouzoff, Winogradoff, and Kolessnikoff. Russkaia medicina, 1886,
Nos. 3 and 32.
[3] Race. Jour. Amer. Water Works Assoc., 1918, 5, 63.
[4] Griffen and Hedallen. Jour. Soc. Chem. Ind., 1915, 34, 530.
[5] Norton and Hsu. Jour. Inf. Dis., 1916, 18, 180.
[6] Rideal, S. Jour. Roy. San. Inst., 1910, 31, 33.
[7] Dakin, Cohen, Duafresne, and Kenyon. Proc. Roy. Soc., 1916, 89B,
232.
[8] Noyes and Lyon. Jour. Amer. Chem. Soc., 1901, 23, 460.
[9] Bray and Dowell. Jour. Amer. Chem. Soc., 1917, 39, 905.
[10] Jakowkin. Zeit. f. Phys. Chim., 1899, 19, 613.
[11] Cross and Bevan. Jour. Soc. Chem. Ind., 1898, 28, 260.
[12] Breteau. Jour. Pharm. Chim., 1915, 12, 248.