G. A. Henty 
By Sheer Pluck [PDF ebook] 
A Tale of the Ashanti War

Frank Hargate is not your average teenage boy. He’s a dedicated amateur scientist whose evenhanded demeanor often comes in handy, such as in the case when he is able to avert a tragedy by saving several classmates from drowning. Based on his valor, he is selected to serve as an assistant to a well-known naturalist on a two-year expedition into the heart of Africa.