James Mitchell joined the Army Medical Corps in 1810. He served in the Napoleonic wars.
Arrival in the Colony
In 1821 he joined the 48th Regiment and arrived in New South Wales as assistant surgeon to the 48th on the John Barry on 7th November 1821.
Colonial Medical Department
In 1823, James Mitchell was appointed to the Colonial Medical Department from the Half-Pay of the Army, which he had been placed on the reduction of the 48th Regiment in 1822, after having been for nine years actively employed in Spain, America, the Netherlands, and the West Indies.
On his appointment to the Colonial Service he was in charge of the Sydney Civil Hospital until September 1837, being over twelve years service. 
James Mitchell first came to the Hunter region in October 1822 on the Elizabeth Henrietta. In March 1823 he came again accompanied by Helenus and Robert Scott and John Cheers.
James Mitchell was granted 2000 acres of land which he selected at Glendon Brook near Singleton. His estate adjoined that of Helenus and Robert Scott.
He didn't settle on his Hunter River grant as he continued to work in the Colonial Medical Department at Sydney Hospital.
Augusta Maria Scott, sister of Robert, Helenus and Alexander Walker Scott, accompanied her mother to Australia in 1832 . In 1833 she married James Mitchell. Their son David Scott Mitchell, founder of the Mitchell library was born in 1836.
4). Burwood Copper Smelting Works, Merewether, c.1852. - University of Newcastle Cultural Collections. Click to enlarge
The Newcastle Sun 26 February 1963
7). A correspondent to the Maitland Mercury in 1851 gives an account of the Copper Smelting Works.......
About three miles from Newcastle, on Dr. Mitchell's Burwood Estate, there is a small glen, so surrounded with hills as to form a natural amphitheatre, the area of which abuts on that portion of the sea-shore known as the Long Beach. On this area, as near as convenient to the water edge, the company's works have been erected, under the superintendence and direction of Mr. Morgan. To this place there is a carriage road from the town. Diverging from the highway to Lake Macquarie, at the commencement of the Burwood estate, it passes over a portion of it, and finally (on its near approach to the works) through a tunnel excavated in a seam of coal eight feet thick, which lies embedded nearly horizontally in the high ridge forming the northern side or wall of the glen. During the last session of Council an act was passed to authorise the formation of a tram-road from this tunnel to the port. Should the design be carried into effect, it will afford the utmost facility of access to the works. The works
consist of a spacious and well-built brick building, 150 feet x 30 feet; two calcining, two melting, and two roasting furnaces, a refinery, smiths' and carpenters' shops, &c. A space at one end of the main building has been set apart for a counting-house and stores, and in the side wails of the same building large arches have been formed to permit approach to the furnaces, which are ranged under detached roofs, running parallel therewith. By this arrangement the interior of the works in which the workmen are chiefly employed can be kept comparatively cool. With the exception of the manager's residence, and the cottages for the work people now in course of erection, the buildings are compactly enclosed within a high and closely paled fence, the whole forming it is to be hoped the germ of a great and prosperous establishment. (Maitland Mercury 6 September 1851)
 (NRS 937) Copies of letters sent within the Colony, 1814-1825 Item: 4/3507 Page: 408 Ancestry.com. New South Wales, Australia, Colonial Secretary's Papers, 1788-1825