a saucepan, and is kept cool
by the external application of cold water; and in this case the still takes
the form represented by the subjoined diagrams; such compact and portable
stills being largely employed in Ireland for the private manufacture of
whisky.

[Illustration]

It is scarcely necessary to say that the condensed water trickles down on
the inside of the cone, and flows out at the spout.

An extemporized arrangement of a similar character may be made by passing a
tobacco pipe through the side of a tin saucepan as shown below, and
inverting the lid of the saucepan; if the lid is now kept cool by frequent
changes of water inside it, and the pipe is properly adjusted so as to
catch the drippings from the convex side of the lid, a considerable
quantity of distilled water may be collected in an hour or so.

The proportion of solid impurities present in water as ordinarily met with
is extremely variable: rain water which has been collected toward the end
of a storm contains only a minute fraction of a grain per gallon, while
river or spring water may contain from less than thirty grains per gallon
or so and upward. Ordinary sea water generally contains from three to four
per cent. of saline matter, but that of the Dead Sea contains nearly
one-fourth of its weight of salts.

[Illustration]

The three impurities of water which most interest the photographer are lime
or magnesia salts, which give the so-called hardness; chlorides (as, for
example, chloride of sodium or common salt), which throw down silver salts;
and organic matter, which may overturn the balance of photographic
operations by causing premature reduction of the sensitive silver
compounds. To test for them is easy. Hardness is easily recognizable by
washing one's hands in the water, the soap being curdled; but in many cases
one must rather seek for a hard water than avoid it, as the tendency of
gelatine plates to frill is far less in hard water than in soft water. It
is, indeed, a common and useful practice to harden the water used for
washing by adding half an ounce or an ounce of Epsom salts (sulphate of
magnesia) to each bucket of water. Chlorides--chloride of sodium or common
salt being that usually met with--may be detected by adding a drop or two
of nitrate of silver to half a wineglassful of the water, a few drops of
nitric acid being then added. A slight cloudiness indicates a trace of
chlorides, and a decided milkiness shows the presence