Irish Sea are about 30 per mille.
English Channel are about 31 "
Beyond the Eddystone are 32 "
As the requirement for a potable sea water does not arise except in
mid-ocean, the proportion of 32 per mille must be taken as the basis of
calculation.
This represents as near 20 per mille of chlorine as possible.
From the analysis shown it will be perceived that the chlorides of
sodium and magnesium are in great preponderance.
It is to the former of these that the baneful effects of sea water when
drunk are to be ascribed, for chloride of sodium or common salt produces
thirst probably by its styptic action on the salivary glands, and scurvy
by its deleterious action on the blood when taken in excess.
Sodium chloride being the principal noxious element in sea water, and
soda in combination with a vegetable or organic acid, such as citric
acid, tartaric acid, or malic acid, being innocuous, the conclusion is
that the element of evil to be avoided is _chlorine_.
After describing various experiments, and calling attention to the power
of earthy matters in abstracting salts from solutions by which he hoped
the process would be perfected, an imperial pint of water from beyond
the Eddystone was shown mixed with 960 grains of citrate of silver and 4
grains of the free citric acid.
Each part of the chlorides requires three parts by weight of the silver
citrate to throw down the chlorine, thus:
3NaCl + Ag_{3}C_{6}H_{5}O_{7} = Na3.C_{6}H_{5}O_{7}+3AgCl.
The silver chloride formed a dense insoluble precipitate, and the
supernatant fluid was decanted and filtered through a rubber tube and
handed round as a beverage.
It contained in each fluid ounce by calculation about:
18 grains of citrate of soda.
1-1/2 " " magnesia.
1/2 " " potash.
1 " sulphate of magnesia.
1/2 " " lime.
1/5 " citric acid.
with less than half a grain of undecomposed chlorides.
To analyze this liquid therapeutically, it may be broadly stated that
salts of potash are _diuretic_, salts of magnesia _aperient_, and salts
of soda _neutral_, except in excessive doses, or in combination with
acids of varying medicinal action; thus, soda in nitric acid, nitrate
of soda, is a _diuretic_, following the law of nitrates as nitrate of
potash, a most powerful diuretic, nitrous ether, etc.; while soda in
combination with sulphuric acid as sulphate of soda is _aperient_,
following the law of sulphates, which increase aperient action, as in
sulphate of magnesia, etc.
Thus it would seem that soda holds the scales evenly between potash and
magnesia in this medical sense, and that it is weighed, so to speak, on
either side by the kind of mineral acid with which it may be combined.
With non-poisonous vegetable acids, and these slightly in excess, there
is not such an effect produced.
Sodium is an important constituent of the human body, and citric acid,
from its carbon, almost a food. Although no one would advocate saline
drinks in excess, yet, under especial circumstances, the solution of it
in the form of citrate can hardly be hurtful when used to moisten the
throat and tongue, for it will never be used under circumstances where
it can be taken in large quantities.
In the converted sea water the bulk of the solids is composed of inert
citrate of soda. There is a little citrate of potash, which is a feeble
diuretic; a little citrate and sulphate of magnesia, a slight aperient,
corrected, however, by the constipatory half grain of sulphate of lime;
so that the whole practically is inoperative.
The combination of these salts in nature's proportions would seem to
indicate that they must be the best for administration in those ailments
to which their use would be beneficial.
Citrate of silver is an almost insoluble salt, and requires to be
kept from the light, air, and organic matter, it being very easily
decomposed.
A stoppered bottle covered with India-rubber was exhibited as indicating
a suitable preserver of the salt, as it affords protection against
light, air, and breakage. As one ounce of silver citrate will convert
half a pint of sea water into a drinkable fluid, and a man can keep
alive upon it a day, then seven ounces of it will keep him a week, and
so on, it may not unreasonably be hoped, in proportion.
It is proposed to pack the silver citrate in hermetically sealed rubber
covered bottles or tubes, to be inserted under the canisters or thwarts
of the life-boats in ocean-going vessels, and this can be done at a
simple interest on the first outlay, without any loss by depreciation,
as it will always be worth its cost, and be invaluable in case of need.
* * * * *