r Rivulets near a Camp, and the Men are
supplied from Wells, if the Water is not pure, very often the digging
of deep Pits, and covering the Bottom and Sides with large Stones, and
over these a Lay of Sand, Gravel, or Chalk, will make the Water pure
in a few Hours.

In fixed Camps, where the Water is bad, _Portius_[144] proposes
straining it thro' Sand, and has given Figures of Machines to be used
for that Purpose; but the Method proposed by Dr. _Lind_ is still more
simple, which is, to get a broad Cask with one End struck out; then
put a longer Cask, with both Ends struck out, in the Middle of it;
fill the short Cask one-third with Sand, and the inner longer Cask
above one-half; fill the Rest of the inner Cask with the Water, which
will filter through the Sand, and rise above the Sand in the outer
Cask, where it may be allowed to run off into Vessels placed to
receive it, by Means of a Cock, put into the Side of the outer Cask,
fifteen or twenty Inches above the Level of the Sand.

[144] See the Treatise published by Dr. _Luc. Anton. Portius_
in 1686, _de Militis in castris sanitate tuenda_, _part._ ii.
_cap._ vi. In this Book we have many useful Things mentioned
relative to the Health of Soldiers.

Where there are no such Conveniences for purifying the Water, what is
used for Drink ought to be mixed with a small Proportion of Spirits,
or Wine, or with Vinegar, or Cream of Tartar, when neither of the
other two can be got; and if the Water be previously boiled, it will
be so much the better.

In Expeditions into warm Countries, where fresh Water is difficult to
be had, a few Stills, with a proper Apparatus, ought to be carried
out; and after a Landing is made, the Stills ought to be set to work
for distilling fresh Water from Sea Water in the Manner mentioned by
Dr. _Lind_[145]; and although a sufficient Quantity cannot be
distilled for serving the whole Army, yet enough may be got in this
Way for the Use of the Sick.

[145] Dr. _Lind_ relates a Number of Experiments of his
having distilled Sea Water in different Manners, as
recommended by others; and concludes, that the best Way of
getting fresh Water from Salt, is to distil the Sea Water by
itself, without any Mixture; and he proposes having a Still
Head to the Coppers or Iron Pots in which the Meat is dressed
aboard a Ship. _Ibid. note to p. 84_, &c.

When Men are very warm, after long Marches, and other hard Duties