City in the Sahara by Jules Verne/Michel Verne

Science fiction when it was written in 1919, with many of the mechanical devices described in the book, now used in reality. This title is the 2nd part of a two part story The Astonishing Adventure of the Barsac Mission where a mission into French West Africa nearly ends in disaster when its members are captured and brought to Blackland, a mysterious city in the desert. The 1st part is entitled Into the Niger Bend. Michel Verne, Jules Verne's son re-wrote some of his late father's works.