There are three times that the Constitution, as it was originally written, mentions slavery. Note however, that the word slavery was never used. First, the 3/5th Clause allowed for three out of every five slaves to be used for population in determining the number of representatives from each state. Second, is the outlawing of the international slave trade in 1808. Finally, there is the fugitive slave law which states that runaway slaves must be returned to their owners even if they are living in free states.
Historically Speaking 