The condition of the slave was a little different then the conditions of the factory workers. Majority of the slaves in the south worked in the cotton fields, which in 1840 accounted for half the value of all America exports. The slaves planted and picked all the cotton that formed the foundation of the 19th century, and the southern economy. Now since the slaves were exposed to the elements all the time a large portion of them was wiped out because of sickness and disease. Slavery rooted from racism and economic exploitation.
In my opinion to call a factory worker back then a wage slave is a correct term to use for them. They were slaves in a factory. A large number of those workers were children under the age of ten, and some times they got brutally wiped. The workers were not allowed to form a union so obviously they were under paid and over worked.