Mary Beth Norton et al., A People and A Nation: A History of the United States, 4th ed. (Boston: Houghton Mifflin Company, 1994), 361-362.
The ranks of free people of color were constantly increased by ex-slaves. Some, like Fredrick Douglass and Harriet Tubman, were fugitives. Douglass had paid his owner $3 a month for the privilege of hiring himself out as a ship caulker in Baltimore. Living among free workers gave him an opportunity to escape slavery. By masquerading as a free black with the help of borrowed seaman’s papers, he bluffed his way to Philadelphia and freedom. Tubman, a slave in Maryland, escaped to Philadelphia in 1849 when it was rumored that she would be sold out of the state. Within the next two years she returned twice to free her two children, her sister, her mother, and her brother and his family. Other slaves were voluntarily freed by their owners. Some, like a Virginia planter named Sanders who settled his slaves as freedmen in Michigan, sought to cleanse their souls by freeing their slaves in their wills. Others freed elderly slaves after a lifetime of service rather than support them in old age. Whites who inherited the parents of the slave Isabella (Sojourner Truth), for example, freed them to avoid supporting the father, who was too old to work.