urities, and then
evaporated back again into salt, precisely as we are doing now.'

"`What colour is the salt-rock, papa?'

"`When pure it is white; but it assumes various colours, according to
what substances may be found mixed with it. It is often yellow, and
flesh-coloured, and blue.'

"`How pretty it must be!' exclaimed Harry; `like precious stones, I
declare.'

"`Yes, it is a precious stone,' rejoined his brother; `more precious, I
take it, than all the diamonds in the world. Is it not, papa?'

"`You are quite right,' I replied. `Salt-rock is more valuable to the
human race than diamonds; though they, too, have an _absolute_ value,
besides their value as a mere ornament. There are some important uses
in arts and manufactures to which they can be applied.'

"`But, papa,' again inquired Frank, determined to know everything he
could about the article of salt, `I have heard that salt is made of
sea-water. Is it so?'

"`Vast quantities of it.'

"`How is it made?'

"`There are three ways of obtaining it:--First, in warm climates, where
the sun is strong, the sea-water is collected into shallow pools, and
there left until it is evaporated by the sun's rays. The ground where
these pools are made must neither be muddy nor porous, else the salt
would get mixed with the mud and sand. Of course the people who
manufacture it in this way take care to choose firm, hard ground for the
bottoms of their pools. There are sluices attached to these pools by
which any water that may not evaporate is drawn off. Salt is made in
this manner in many southern countries--in Spain and Portugal, in
France, and other countries that lie around the Mediterranean; also in
India, China, Siam, and the island of Ceylon.

"`The second way of making salt from sea-water is precisely the same as
that I have described--except that, instead of these artificial pools,
the evaporation takes place in broad tracts of country over which the
sea has spread in time of high springtides. When the sea falls again to
its proper level, it leaves behind it a quantity of water in these
tracts, which is evaporated by the sun, leaving behind it fields of pure
salt. Nothing remains to be done but to scrape this salt into heaps and
cart it off; and at the next spring-tide a fresh influx of sea-water
produces a new crop of salt, and so on. This kind is better than that
which is made in the artificial pools--though neither of them is equal
to the salt