Knapp's name disappears from the masthead as printer of The Liberator as of January of 1840. In the July 24, 1840, issue, there is an advertisement for the abolitionist printers Dow and Jackson "successors to Isaac Knapp".
We do not have Knapp's story of how and why this happened. Garrison described him as "a most loving, faithful, devoted friend and brother.... He was naturally amiable, kind, and obliging even to excess.... He deserves pity rather than censure, and never can I find it in my breast to say a bitter word of him.... I am not sure that I could have commenced the printing of the Liberator, had it not been for his uniting with me in partnership, and participating in the labors and necessities of my lone situation." However, according to Garrison, "he was altogether too generous...and having no business adaptation, be consequently involved himself deeply in debt while attempting to carry on business. It was thus he became depressed in spirit, and, instead of calmly submitting to the stroke of adversity, vainly sought to find relief from his sorrows (as millions have done before) in the intoxicating bowl." "[H]is disconnexion with the Liberator ...[was] absolutely essential to the existence of the paper."
In 1841 Knapp complained that "he has been deprived of his interest in the Liberator unjustly--that Mr. Garrison and 'a certain rich man' have treated him badly--therefore he intends to print a paper to be called 'Knapp's Liberator'." Only one issue of this paper is known to have been published, on January 8, 1842 (only known copy at the Massachusetts Historical Society).
Titles listed: Abolition of the Slave Trade, Adams' Letters, Adams' Oration, Adin Ballou's Discourse, Anti-Slavery Catechism, Anti-Slavery Manual, Anti-Slavery Record, Archy Moore, Authentic Anecdotes of American Slavery, Barrows on the Slave Question, Birney's Second Letter, Bourne's Picture, British Apprenticeships, Channing on Slavery, Channing on Texas, Charles Ball, Chloe Spear, Crandall's Trial, Discussion, Dissertation on Servitude, Dresser, Stones' Letters, &c., Enemies of the Constitution Discovered, Evils and Cure, Godwin on Slavery, Granville Sharp, Gustavus Vassa, Important Pamphlet, James Jackson, Jay's Inquiry, Juvenile Poems, Kentucky Address, Lemuel Haynes, Liberty, Memoir of Phillis Wheatley, Miss Beecher Reviewed, Miss Grimke's Appeal, Miss Grimke's Epistle, Mott's Sketches, Mrs. Child's Appeal, Mrs. Stewart's Productions, Objections Answered, Our Liberties in Danger, Phillis Wheatley, Rankin's Letters, Right and Wrong in Boston, Slave Produce, Slave's Friend, Smith's Bible Argument, Songs of the Free, Stanton's Remarks, Stewart's West India Question, Testimony of God Against Slavery, The Fountain, The Generous Planter, The Negro Pew, The Oasis, Thompson at Manchester, Thompson in America, Thompson in G. Britain, Thompson's Lectures and Debates, Valuable Documents, Vigilance Committee, Whittier's Poems, Wilberforce.
^The National cyclopaedia of American biography, being the history of the United States as illustrated in the lives of the founders, builders, and defenders of the republic, and of the men and women who are doing the work and moulding the thought of the present time, edited by distinguished biographers, selected from each state, revised and approved by the most eminent historians, scholars, and statesmen of the day. 2. New York: James T. White. 1910.