Our readers are well aware that water as found naturally is never
absolutely free from dissolved impurities; and in ordinary cases it
contains solid impurities derived both from the inorganic and organic
kingdoms, together with gaseous substances; these latter being generally
derived from the atmosphere.
By far the purest water which occurs in nature is rain-water, and if
this be collected in a secluded district, and after the air has been
well washed by previous rain, its purity is remarkable; the extraneous
matter consisting of little else than a trace of carbonic acid and other
gases dissolved from the air. In fact, such water is far purer than any
distilled water to be obtained in commerce. The case is very different
when the rain-water is collected in a town or densely populated
district, more especially if the water has been allowed to flow over
dirty roofs. The black and foully-smelling liquid popularly known as
soft water is so rich in carbonaceous and organic constituents as to be
of very limited use to the photographer; but by taking the precaution of
fitting up a simple automatic shunt for diverting the stream until the
roofs have been thoroughly washed, it becomes possible to insure a good
supply of clean and serviceable soft water, even in London. Several
forms of shunt have been devised, some of these being so complex as
to offer every prospect of speedy disorganization; but a simple and
efficient apparatus is figured in _Engineering_ by a correspondent who
signs himself "Millwright," and as we have thoroughly proved the value
of an apparatus which is practically identical, we reproduce the
substance of his communication.
A gentleman of Newcastle, a retired banker, having tried various filters
to purify the rain-water collected on the roof of his house, at length
had the idea to allow no water to run into the cistern until the roof
had been well washed. After first putting up a hard-worked valve, the
arrangement as sketched below has been hit upon. Now Newcastle is a very
smoky place, and yet my friend gets water as pure as gin, and almost
absolutely free from any smack of soot.
[Illustration]
The sketch explains itself. The weight, W, and the angle of the lever,
L, are such, that when the valve, V, is once opened it goes full open. A
small hole in the can C, acts like a cataract, and brings matters to a
normal state very soon after the rain ceases.
The proper action of the apparatus can only be insured by a careful
adjustment of the weight, W, the angle through which the valve opens,
and the magnitude of the vessel, C. It is an advantage to make
the vessel, C, somewhat broader in proportion to its height than
represented, and to provide it with a movable strainer placed about half
way down. This tends to protect the cataract hole, and any accumulation
of leaves and dirt can be removed once in six months or so. Clean soft
water is valuable to the photographer in very many cases. Iron developer
(wet plate) free from chlorides will ordinarily remain effective on the
plate much longer than when chlorides are present, and the pyrogallic
solution for dry-plate work will keep good for along time if made with
soft water, while the lime which is present in hard water causes the
pyrogallic acid to oxidize with considerable rapidity. Negatives that
have been developed with oxalate developer often become covered with a
very unsightly veil of calcium oxalate when rinsed with hard water, and
something of a similar character occasionally occurs in the case of
silver prints which are transferred directly from the exposure frame to
impure water.
To the carbon printer clean rain-water is of considerable value, as he
can develop much more rapidly with soft water than with hard water;
or, what comes to the same thing, he can dissolve away his superfluous
gelatine at a lower temperature than would otherwise be necessary.
The cleanest rain-water which can ordinarily be collected in a town is
not sufficiently pure to be used with advantage in the preparation of
the nitrate bath, it being advisable to use the purest distilled water
for this purpose; and in many cases it is well to carefully distill
water for the bath in a glass apparatus of the kind figured below.
[Illustration]
A, thin glass flask serving as a retort. The tube, T, is fitted
air-tight to the flask by a cork, C.
B, receiver into which the tube, T, fits quite loosely.
D, water vessel intended to keep the spiral of lamp wick, which is shown
as surrounding T, in a moist condition. This wick acts as a siphon, and
water is gradually drawn over into the lower receptacle, E.
L, spirit lamp, which may, in many cases, be advantageously replaced by
a Bunsen burner.
A small metal still, provided with a tin condensing worm, is, however, a
more generally serviceable arrangement, and if ordinary precautions are
taken to make sure that the worm tube is clean, the resulting distilled
water will be nearly as pure as that distilled in glass vessels.
Such a still as that figured below can be heated conveniently over an
ordinary kitchen fire, and should find a place among the appliances
of every photographer. Distilled water should always be used in the
preparation of emulsion, as the impurities of ordinary water may often
introduce disturbing conditions.--_Photographic News_.
[Illustration]
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