Problem: Columbus Delano, (June 4, 1809 - October 23, 1896) was a lawyer, rancher, banker, statesman and a member of the prominent Delano family. Delano was elected U.S. Congressman from Ohio, serving two full terms and one partial one. Prior to the American Civil War, Delano was a National Republican and then a Whig; as a Whig he was identified with the faction of the party that opposed the spread of slavery into the Western territories, and he became a Republican when the party was founded as the major anti-slavery party after the demise of the Whigs in the 1850s. During Reconstruction Delano advocated federal protection of African-Americans civil rights, and argued that the former Confederate states should be administered by the federal government, but were not part of the United States until they met the requirements for readmission to the Union.

In 1875, Delano's reputation for personal honesty came under increasing scrutiny as revelations of corruption in the Grant administration continued to be the subject of investigations and media revelations. Westerners unhappy with Delano's rulings on land grants and other issues accused Delano's son John, an employee of the Interior Department, of corruption, bribery, and fraud. Governor Edward M. McCook of the Colorado Territory, claimed that John Delano had accepted a $1,200 bribe from a Colorado banker, Jerome B. Chaffee, to secure land patents from the Department of Interior. The New-York Tribune reported that John Delano was profiteering through Interior's Office of the Surveyor General by accepting partnerships in Wyoming surveying contracts without having been trained in surveying or map making, and without providing any meaningful contribution to the fulfillment of the contracts; the obvious implication was John Delano had taken extortion money from illicit contract agreements. In March 1875, the former chief clerk of the Surveyor's Office, L. C. Stevens, wrote to Benjamin Bristow, Grant's Secretary of the Treasury, stating that Surveyor General Silas Reed had made several corrupt contracts which financially benefited John Delano. Stevens also said both Reed and John Delano had blackmailed five deputy surveyors for $5,000. More damaging was Stevens' charge that Columbus Delano knew and approved of what Reed had done for John Delano. Both Bristow and Secretary of State Hamilton Fish demanded that Grant fire Delano. Grant declined, telling Fish, "If Delano were now to resign, it would be retreating under fire and be accepted as an admission of the charges." The controversy did not abate; by mid-August it became clear that Delano could not remain in office; Delano offered his resignation and Grant accepted, but Grant did not make it public. Grant finally announced his acceptance of Delano's resignation on October 19, 1875, after Bristow threatened to resign if Delano was not replaced. Grant replaced Delano with Zachariah Chandler, who quickly initiated civil service and other reforms in the Department of the Interior. Delano's administration was investigated by Congress, Chandler, and a special presidential commission; his personal conduct was exonerated, but his reputation as an honest, capable administrator was damaged, and Delano never again ran for office or served in an appointed one. In April 1876, The Committee on the Expeditures in the Interior Department confirmed that Reed had set up an illicit slush fund for John Delano's financial benefit, and that Delano thanked Reed while also telling him "to be careful to do nothing that would have the semblance of wrong."

why did he resign?

Answer with quotes: In 1875, Delano's reputation for personal honesty came under increasing scrutiny as revelations of corruption in the Grant administration continued to be the subject of investigations and media revelations.

Question:
Born in Scotland on 15 June 1792, he was son of John Mitchell of Carron Works and was brought up from childhood by his uncle, Thomas Livingstone of Parkhall, Stirlingshire. On the death of his uncle, he joined the British army in Portugal as a volunteer, at the age of sixteen. On 24 June 1811, at the age of nineteen, he received his first commission as 2nd Lieutenant in the 1st Battalion 95th Rifles (later the Rifle Brigade / Royal Green Jackets). Utilising his skills as a draughtsman of outstanding ability, he was occasionally employed in the Quartermaster-General's department under Sir George Murray.
Mitchell's fourth expedition was into Queensland in 1845-46. He was convinced that a significant river must flow north-west into the Gulf of Carpentaria, this being the main thrust of the endeavour. On 15 December 1845 Mitchell started from Boree (Buree in Mitchell's journal) with a large party including Edmund Kennedy as second in command (later speared to death at Escape River near Cape York). He struck the Darling River above Fort Bourke then continued to the Narran River, the Balonne, and the Culgoa. On 12 April 1846 he came to a natural bridge of rocks on the main branch of the Balonne which he called St.George Bridge, now the site of the town of St George. Kennedy was left in charge of the main body here, and was instructed to follow on slowly while Mitchell pushed ahead with a few men. Mitchell followed the Balonne to the Maranoa, and the Cogoon (now called Muckadilla Creek, near Roma). This rivulet led him to a magnificent pastoral district in the midst of which stood a solitary hill that he named Mount Abundance. He then crossed a low watershed to the Maranoa and awaited Kennedy's arrival. Kennedy rejoined Mitchell on 1 June 1846. Leaving Kennedy for a second time, he set out on an extensive excursion of more than four months. Mitchell traversed the country at the head of the Maranoa and discovered the Warrago River. Keeping north over the watershed, he traversed the Claude and Nogoa rivers, then reached the Belyando River, an upper reach of the Burdekin River. This had already been discovered by Ludwig Leichhardt on his expedition to Port Essington on 2 April 1845. Intensely mortified to find that he was on a tributary of the Burdekin River, and approaching the ground already trodden by Leichhardt, he returned to the head of the Nogoa and struck west, after dividing his party and forming a stationary camp. He continued west, making a new discovery which he was certain was the fabled north-west river. In honour of the sovereign of the time he decided to call it Victoria River. Having run out of time, he turned back towards the main party. It was here that Mitchell first noticed the well known grass that bears his name. On the homeward journey he trekked along the Maranoa River to St.George Bridge, arriving in Sydney 20 January 1847. Later that year, Kennedy proved beyond doubt that the Victoria did not continue north-west, but turned south-west and joined Cooper Creek. He renamed the watercourse the Barcoo River from a name mentioned by local Aborigines.
Answer this question using a quote from the text above:

How long did the expedition last?

Answer:
On the homeward journey he trekked along the Maranoa River to St.George Bridge, arriving in Sydney 20 January 1847.