I’m afraid that’s not gold. It’s a 40 para coin of Abdülmecid I and these were struck in copper.
The reverse says “may he be victorious” and “struck in Constantinople” around the value “40” in Arabic numerals, with the Islamic calendar year 1255 below (1855-1861 in the Western calendar). The obverse has Abdülmecid’s tughra seal and Arabic numbers for “year 18” which puts it at 1856 in the Western calendar.
Not of any real value, unfortunately.