interior countries with salt, a scarce and valuable commodity, as I
frequently and painfully experienced in the course of my journey.
Considerable quantities of this article, however, are also supplied
to the inland natives by the Moors, who obtain it from the salt pits
in the Great Desert, and receive in return corn, cotton cloth, and
slaves.

In their early intercourse with Europeans the article that attracted
most notice was iron. Its utility, in forming the instruments of
war and husbandry, make it preferable to all others, and iron soon
became the measure by which the value of all other commodities was
ascertained. Thus, a certain quantity of goods, of whatever
denomination, appearing to be equal in value to a bar of iron,
constituted, in the traders' phraseology, a bar of that particular
merchandise. Twenty leaves of tobacco, for instance, were
considered as a bar of tobacco; and a gallon of spirits (or rather
half spirits and half water) as a bar of rum, a bar of one commodity
being reckoned equal in value to a bar of another commodity.

As, however, it must unavoidably happen that, according to the
plenty or scarcity of goods at market in proportion to the demand,
the relative value would be subject to continual fluctuation,
greater precision has been found necessary; and at this time the
current value of a single bar of any kind is fixed by the whites at
two shillings sterling. Thus, a slave whose price is 15 pounds, is
said to be worth 150 bars.

In transactions of this nature it is obvious that the white trader
has infinitely the advantage over the African, whom, therefore, it
is difficult to satisfy, for conscious of his own ignorance, he