How did scientific discoveries of the late 19th century allow european powers the ability to finally conquer the interior of africa?

The Industrial Revolution allowed for the fabrication of any items necessary for the safe and fast exploration and colonization of the African hinterland. The output was so great that colonial powers could count on a steady flux of necessary supplies of all kinds (weapons, tools, medical instruments, navigation instruments, irrigation systems, electrical systems, steam engines and so forth). There were also a great number of medical advances that protected European explorers, settlers and colonial troops from infectious diseases and extreme weather temperatures. It was indeed around 1850 that quinine started to be produced in industrial quantities for the treatment of malaria.

b. british workers