iodine concentration of 8 mg/l. A major ad-
vantage of tetraglycine hydroperiodide tablets
is their convenience. A small bottle of fifty
tablets can be carried easily. Sealed bottles
can be stored for months with little loss of io-
dine. The manufacturer of Potable-Aqua
®
claims four years.
The principal disadvantage of tetraglycine
hydroperiodide is its tendency to dissociate
after exposure to air. In studies to document
their stability, tetraglycine hydroperiodide
tablets placed in a single layer in an open dish
at 60ºC (140ºF) lost 40 percent of their iodine
in seven days. At room temperature and 100
percent humidity, the tablets lost 33 percent of
their iodine in four days. Studies to determine
the rate of dissociation of tablets in a small
bottle opened several times a day for one or
two weekends a month, the pattern of week-
end outdoorsmen, have not been reported.
Tetraglycine hydroperiodide tablets (and
other iodine preparations) add a definite
brown color to the water if 8mg/l is present.
Tightly capping and refrigerating bottles of
the tablets may help retard iodine loss, but
they probably should be discarded a few
months after opening. The manufacturer of
Potable-Aqua
®
recommends a year.
Saturated Aqueous Iodine Solution
In 1975 Kahn and Visscher described a
procedure for disinfecting water with a satu-
rated aqueous solution of iodine. Iodine crys-
tals (2 to 8 g, USP grade, resublimed) are
placed in a 30 cc (1 oz) clear glass bottle with
a paper lined Bakelite cap. (The details are
important.) The bottle is filled with water,
shaken vigorously, and allowed to stand for
one hour to produce a saturated solution. One
half of this saturated solution (15 cc) is poured
into one liter of water to be disinfected. If the
temperature of the water in the 30 cc bottle is
20ºC (68ºF) or higher, which can be achieved
easily by carrying the bottle in a shirt pocket,
the iodine concentration in the disinfected wa-
ter would be about 9 mg/l.
Saturated aqueous iodine solutions have
two distinct advantages:
The bottle contains enough iodine to disin-
fect up to 8,000 liters of water, depending on
how it is used;
If crystals can be seen in the bottom,
enough iodine for disinfection is known to be
present, so the system is totally reliable.
This technique for water disinfection has
been denounced, even in terms such as "it can
kill you," because in decanting the super-
natant, iodine crystals could be poured into
the water to be consumed. This hazard ap-
pears insignificant. Iodine is so weakly toxic
that three or four crystals would not be ex-
pected to produce any symptoms. Individuals
who have used this technique extensively
have found that small flakes of iodine are
commonly caught by surface tension in the
small bottle, poured into the large bottle, and
ingested without producing any detectable ill
effects. A jar with a sleeve in its neck to pre-
vent decanting the iodine crystals, "Polar
Pure," is commercially available. On its sur-
face this jar also has a temperature indicator
and data for calculating the volume of satura-
ted iodine solution that would contain 8 mg of
iodine. However, this jar is too large to fit into
a shirt pocket.
A saturated aqueous solution of iodine has
been singled out as being uniquely ineffective
at low temperatures for eradicating giardia
cysts. However, all of the disinfectants tested
in that study produce their antimicrobial ef-
fects by releasing diatomic iodine. A differ-
ence in effectiveness when all act through the
