The Earl of Dundonald's Method of Purifying Sea Salt

THE EARL OF DUNDONALD’S METHOD OF PURIFYING SEA SALT.
               [From the Edinburgh Philosophical Transactions.]
HIS Lordship’s process proceeds upon
this observation: That the common
sea salt possesses a mixture of ingredients,
which render it in a great degree unfit for
preserving victuals. These ingredients ap-
pear, by experiment, to be nauseous, bit-
ter, and cathartic salts, having an earthy
basis, which are intimately mixed with the
proper sea salts.
    To purify salt, by dissolving it in water,
decompounding the bitter salts, and preci-
pitating their earthly basis, by adding a fix-
ed alkali, is a tedious process, too expen-
sive, and even imperfect.
    Lord Dundonald observed, that hot wa-
ter, saturated with sea salt, will still dis-
solve a great part of the bitter earthy salts.
His method, therefore, of purifying com-
mon salt from these bitter salts is, to take
a conical vessel, having a hole in the small
end, which is to be undermost; to place
it, filled with common salt, in a moderate
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heat; to take one twentieth part of the
salts contained in it, and putting it in an
iron pan, to dissolve it in such a proportion
of water, as that the water shall be com-
pletely saturated with the salt; then pour
this solution boiling hot on the salt in the
conical vessel, which is to be purified.
The boiling water being already saturated
with sea salt, will dissolve no more in it,
but will dissolve much of the bitter earthy
salts, and this solution will gradually drop
out at the hole at the bottom of the case.
When it ceases to drop, the same process
is to be repeated by means of fresh porti-
ons of the same parcel of salt, already
partly purified, till it be brought to the
required degree of purity.
    The superiority of salt thus purified is 
obvious to the taste, and by its effect in 
preserving, fish, flesh, and butter; for it
has been often and carefully tried.