A Massive Resource which I have used to examine the character of Pennsylvania Dutch Slavery. Along with the accounts of Peter Williamson and Benjamin Franklin, Irish Old News paints a brutal picture of soul-devouring toil under the Christian whip of the profit-centric protestant Congregationalist pyramid scheme known as Penn's Woods; a forested slave plantation ordained by greed, policed by savage, heathen Indians, blessed by God—a pit into which a million or more souls were fed into the fires of avarice over a century. The sin that was Pennsylvania paved the way for modern corrections systems, municipal licensing, bounty hunting and ultimately the cult of the American frontiersman, as the most able slaves worked, ran or fought their way over the Appalachians, then down the Ohio River and conquered a land dozens of times larger than the slave islands they had been shipped out of.

"Irish Emigration to America, 1723-1773" from Journal of American Irish Historical Society, 1927

...Passing over twenty years, during which there was a constant stream of emigration from Ireland to America, I find another interesting document chronicled under date of May, 1751:

“One hundred and fifty Passengers, including 50 Irish Servants (many of them Catholics who were bound as Servants before the Lord Mayor of Dublin) sailed for Philadelphia, on board the Homer, Captain John Slade, Commander.” The list of names is not complete, owing to damp, but I have made out the following as among those who sailed on the Homer from Dublin, in May, 1751: John O’Toole, Thomas Cassidy, James Fennell, James O’Neill, James Hickey, Edward Doran, John Callaghan, Catherine Cullen, Eleanor Cody, John Connery, Catherine Lawler, William Coffey, John Slattery, Philip MacNeill, Giles Power, Anne Connolly.

O'Malley, Mike. "Runaway from Freedom?" Runaway from Freedom. (30 Aug 2005)

Benjamin Franklin estimated that at the time of the American Revolution, roughly one half of Pennsylvania’s labor force was legally unfree—bound to someone else as property, for many years or for a lifetime.

Such second and third hand sources are available via the link below, along with numerous transcribed slave catcher ads from the 1700s.